User:Serendipodous/indigo/page 19

Rayman

Ahuna Mons cryovolcano, formed less than 240 million years ago (mud, salt, water cryomagma)

20 likely cryovolcaones

Ceres has insulators that allow it to hold onto its heat

Fractures associated with faculae

Eruptions occurred in recent geological time, 4 million years ago- perhaps an imapact?

ceres gravity 1/40 that of earth

More meteorites from Vesta than from Mars or the Moon

Even scaled to size, Ceres is many thousands of times less active than Earth

Juling Crater; ice grew by 500 acres in 6 months- sun heated crater, water sublumated and settled on the cold wall (wall to floor,floor to wall)

Something is making boulders fall down crater walls.

Spacecraft ran out of propellent on Oct 31. Propellant needed for reorientation, set into a ceres kissing orbit

Not allowed to let Dawn come into contact with Ceres for at least 20 years. Many of the ingredients for life, internal heat microbes could live longer than 20 years. Time to concieve launch and fly an astrobiological mission to Ceres. ebtter than 99 percent chance remain in orbit for 50 years; possibly many hundreds of years.

Ceres

https://www.liebertpub.com/doi/full/10.1089/ast.2018.1999

Ceres, the most water-rich body in the inner solar system after Earth

The surface chemistry and internal structure of Ceres testify to a protracted history of reactions between liquid water, rock, and likely organic compounds.

Ceres shares spectral similarities with C-type asteroids, in particular with Hygiea

McCord and Sotin (2005) pointed out that Ceres contains the right amount of both water and rock for sustained heating, resulting in the formation of a volatile-rich shell. This was supported by the early detection of hydrated materials on Ceres' surface (Lebofsky, 1978), suggesting pervasive aqueous alteration (Rivkin and Volquardsen, 2009).

While Ceres does not experience tidal heating, it is sufficiently close to the Sun and contains long-lived radioisotopes (∼73 wt % rock) to potentially preserve brines until present

Castillo-Rogez and McCord (2010) found that Ceres' ice-rich shell could host temperatures as warm as 240 K a few tens of kilometers deep for most of its history.

These models suggest that Ceres could have harbored a global subsurface ocean for several hundred million years after its formation

A major difference between Ceres and other large main belt asteroids lack of a family

salts leached from accreted silicates following hydrothermal processing, the latter of which is inferred from Ceres' pervasively hydrated surface

modeling studies predict that pockets of concentrated brines could exist at the base of the crust today (>50 km deep

(a) Geophysical data confirmed the abundance of water ice and the need for gas and salt hydrates to explain the observed topography and crustal density.

(b) Various types of carbonates and ammonium chloride have been found in many sites across Ceres' surface (e.g., salts exposed on the floor of Dantu crater).

(c) Ernuter crater (∼52 km, above) and its area present carbon species in three forms (reduced in CxHy form, oxidized in the form of carbonates, and intermediate as graphitic compounds.).

(d) Ceres shows extensive evidence for water ice in the form of ground ice and exposure via mass wasting and impacts (Left: Juling crater, ∼20 km).

(e) Recent expressions of volcanism point to the combined role of radiogenic heating and low-eutectic brines in preserving melt and driving activity (Left: Ahuna Mons, ∼4.5 km tall, ∼20 km diameter).

(f) Impacts could create local chemical energy gradients in transient melt reservoirs throughout Ceres' history (Left: Cerealia Facula, ∼14 km diameter).

Measurements of hydrogen by GRaND indicate the presence of a global, subsurface water-ice table at depths less than a few decimeters at latitudes greater than 45°

The GRaND data indicate that the top meter of the regolith contains only about 10 wt % water ice

Water ice is expressed in small-scale regions on Ceres' surface, in association with impact craters and mass wasting.

Ceres' surface also shows a variety of morphologies that testify to abundant water ice in the uppermost ∼10 km of the crust (Sizemore et al., 2019). In particular, lobate flows analogous to water-ice flows on Earth, Mars, and possibly Titan, are also found on Ceres. These lobate flows are morphologically distinct from the predominantly dry mass-wasting processes observed on Vesta and are more numerous toward the cooler poles

pitted terrain in seven impact craters on Ceres so far. The existence of these features has been interpreted as evidence that volatiles buried at shallow depths in Ceres' subsurface have undergone some degree of sublimation following impact-produced heating

Global interior structure for Ceres: a ∼40-km thick (average) strong crust is composed of rock+ice+salts+clathrates with no more than ∼40% ice (Bland et al., 2016; Ermakov et al., 2017a; Fu et al., 2017). It overlays a rocky mantle with a weak upper layer with brine-filled pore space that controls the global shape (Fu et al., 2017). Right: Possible structure of the crust inferred below Occator Crater's faculae, in a region where the crust is ∼50 km thick (Ermakov et al., 2017a). Impact craters could create transient melt chambers. Large impacts could also introduce or re-enact fractures allowing for the upwelling of deep brines. This rendition assumes that the impact melt reservoir was originally larger in extent but is mostly frozen at present, except for brines supplied from the deeper reservoir

The crustal thickness is about 40 km on average, but varies from ∼25 to 55 km (Ermakov et al., 2017a). The low crustal density implies a silicate volume fraction of less than 20% (Ermakov et al., 2017a). However, a crust dominated by water ice is inconsistent with observations of numerous impact craters, other morphological features on Ceres' surface, and ∼16 km of total topographic relief (Bland, 2013; Buczkowski et al., 2016). This suggests that the outer layer is stiffer than previously thought and contains ≤40% water ice and void space by volume (Bland et al., 2016). Furthermore, the crust's high strength and low density have been interpreted as evidence for abundant salts and/or gas hydrates, hereafter referred to as “clathrates,” consistent with a frozen early ocean

Separation of a rocky mantle and ice-rich crust involves at least partial melting of Ceres' volatile phase on a global scale

Ceres had to form early (a few My after the beginning of the solar system) to benefit from additional intense heat from the short-lived aluminum-26 radioisotope.

Another compelling line of evidence for global, pervasive aqueous alteration early in Ceres' history is its hydrated surface of remarkably homogeneous composition

There are little data about this early period left in the present-day geomorphology. Thus, the range of possible ocean lifetimes is bounded by models: from a few hundred million years if the mantle was compact and lithified

possibly until present, if the interior maintained a convecting “mudball” (Travis et al., 2018) or if insulating material in the crust impeded heat loss and helped preserve a liquid briny layer tens of km thick at the base of the crust

Overall, combined gravity and topography data indicate Ceres' density profile is akin to that of the icy moons of the outer Solar System, specifically the ocean-bearing Enceladus.

Ceres' near-infrared spectrum, as observed by VIR, is best fit by a mixture of ammonium-bearing phyllosilicates, magnesium-bearing phyllosilicates, carbonates, and a dark, spectrally featureless component whose nature is unknown

the presence of ammoniated clays and salts, and a greater variety of carbonates. This includes sodium carbonates, which have not been found in CI chondrites

the Occator facula material (and potentially other faculae formed on crater floors) is thought to have originated in liquid brine reservoirs or transient near-surface brines resulting from impact-induced heating

Among other bioessential elements, sulfur has proved elusive. It is predicted to exist on Ceres in the form of sulfides (Castillo-Rogez et al., 2018), but these compounds do not have an obvious signature in the wavelength range of VIR.

Carbon has been found in the form of carbonates and organic compounds. Carbon dioxide and/or methane are also believed to be present in the form of clathrates in the crust

Ceres' dark component is graphitized carbon produced from the weathering of organics by charged particles.

Ceres' surface is relatively old with two regional geological units: the high Hanami Planum that is >2 Gy old (Frigeri et al., 2018), and the surrounding lowlands, which have been interpreted as basins (planitiae) created by large impacts

(1) exposure of fresh material and local resurfacing with ejecta (e.g., Palomba et al., 2019); (2) gardening and mixing of the regolith with ice from the crust (Prettyman et al., 2019b); and (3) in the case of large impacts, input of heat into the crust that could drive local, short-lived activity

However, it was also suggested that the many domes (tholi, montes) found on Ceres' surface (Sizemore et al., 2019) could be formed from episodes of cryovolcanic activity that lasted for several billion years up until the present

Permanently shadowed craters at Ceres' poles that display higher albedos than surrounding areas are likely surficial deposits of water ice

Ceres' surface also shows a variety of morphologies that testify to abundant water ice in the uppermost ∼10 km of the crust. In particular, lobate flows analogous to water-ice flows on Earth, Mars, and possibly Titan, are also found on Ceres. These lobate flows are morphologically distinct from the predominantly dry mass-wasting processes observed on Vesta and are more numerous toward the cooler poles

Pitted terrain in impact craters has been interpreted as evidence that volatiles buried at shallow depths in Ceres' subsurface have undergone some degree of sublimation following impact-produced heating Admittance analysis indicates that Ceres is differentiated into a low-density crust (∼1200–1300 kg/m3) and rocky mantle (2390–2450 kg/m3) (Ermakov et al., 2017a) (Fig. 2). The crustal thickness is about 40 km on average, but varies from ∼25 to 55 km (Ermakov et al., 2017a). The low crustal density implies a silicate volume fraction of less than 20% (Ermakov et al., 2017a).

However, a crust dominated by water ice is inconsistent with observations of numerous impact craters, other morphological features on Ceres' surface, and ∼16 km of total topographic relief (Bland, 2013; Buczkowski et al., 2016). This suggests that the outer layer is stiffer than previously thought and contains ≤40% water ice and void space by volume (Bland et al., 2016). Furthermore, the crust's high strength and low density have been interpreted as evidence for abundant salts and/or gas hydrates, hereafter referred to as “clathrates,” (Bland et al., 2016; Fu et al., 2017) starting a few kilometers below the surface (Sizemore et al., 2019). This is consistent with the outcome of geochemical simulations of the freezing of an early ocean (Castillo-Rogez et al., 2018).

Separation of a rocky mantle and ice-rich crust involves at least partial melting of Ceres' volatile phase on a global scale (McCord and Sotin, 2005). This event must have happened early in a body, whose sole internal heat source is radioisotope decay. Castillo-Rogez and McCord (2010) showed that long-lived radioisotopes alone cannot lead to the separation of a volatile-rich shell. They concluded that Ceres had to form early (a few My after the beginning of the solar system) to benefit from additional intense heat from the short-lived aluminum-26 radioisotope.

the low rocky mantle density indicates that temperatures remained low in the course of Ceres' history, less than the dehydration temperatures of phyllosilicates (>600°C). Beyond these findings, constraints are lacking on Ceres' internal evolution, particularly the period during which the dwarf planet hosted a global ocean. verall, combined gravity and topography data indicate Ceres' density profile is akin to that of the icy moons of the outer Solar System, specifically the ocean-bearing Enceladus. Indeed, gravity data obtained at Enceladus with the Cassini mission also yielded a rocky mantle with a density of ∼2400 kg/m3 (Iess et al., 2014) and an ice-dominated shell.

Convecting mudball?

Dawn observations have confirmed that Ceres' rocky material has been extensively processed by liquid water on a global scale Abundant mineral products of aqueous alteration are exposed on Ceres' surface, providing detailed insight into the chemistry of past and perhaps present liquid water environments.

Ceres' near-infrared spectrum, as observed by VIR, is best fit by a mixture of ammonium-bearing phyllosilicates, magnesium-bearing phyllosilicates, carbonates, and a dark, spectrally featureless component whose nature is unknown ochemical models that include the interaction of liquid water containing carbon- and nitrogen-rich volatiles with silicates and organics of chondritic composition at temperatures below 50°C (Neveu et al., 2017), consistent with conditions expected in Ceres' early ocean

clays and salts sodium carbonate

sodium carbonate is also found in Enceladus' plumes (Postberg et al., 2011) and on Earth, where it is typical of alkaline aqueous environments

This suggests that abundant material of aqueous origin is present at shallow depths.

The carbonate/ammonium/sodium composition of these brines is the same as the liquids that must have equilibrated with the minerals that blanket Ceres' surface (Neveu et al., 2017; Castillo-Rogez et al., 2018). Near the surface, these liquids subsequently underwent freezing and desiccation (Vu et al., 2017; Castillo-Rogez et al., 2018; Thomas et al., 2019). The compositional gradient observed across the dome in the central facula in Occator (called Cerealia Facula) (Raponi et al., 2019) indicates an evolution of the cryomagma source, consistent with modeling by Quick et al. (2019). Ceres' surface is relatively old with two regional geological units: the high Hanami Planum that is >2 Gy old (Frigeri et al., 2018), and the surrounding lowlands, which have been interpreted as basins (planitiae) created by large impacts (Marchi et al., 2016). The latter suggests regional resurfacing accompanied with the removal of 100-km large craters (Marchi et al., 2016). Most of the long-term evolution of Ceres has been driven by impacts with three types of consequences: (1) exposure of fresh material and local resurfacing with ejecta (e.g., Palomba et al., 2019); (2) gardening and mixing of the regolith with ice from the crust (Prettyman et al., 2019b); and (3) in the case of large impacts, input of heat into the crust that could drive local, short-lived activity (Bowling et al., 2019).

he likely role of brines in driving cryovolcanism is indicated by features such as the Occator faculae as well as Ahuna Mons and more ancient features of potentially similar origin

Ahuna Mons is an ∼4-km-high and ∼21-km-wide mountain that is interpreted as a viscous cryovolcanic dome formed by the ascent of cryomagma from the depth and subsequent eruption onto the surface in a manner akin to lava dome emplacement on Venus and Europa his cryomagma is thought to consist of low-eutectic salt melt, ice, and silicate solid (Ruesch et al., 2016). Abundant sodium carbonate is found on the flanks of the mountain

Ahuna Mons' unique large gravity anomaly suggests a low ice content

Based on gravity data analysis, Ruesch et al. (2019a) connect the formation of Ahuna Mons to upwelling of a dense slurry from the mantle.

The bright spots, or faculae observed in the 92-km-diameter crater, mainly consist of sodium carbonates, which may represent the residue of crystallized brines extruded onto the crater floor from depth (De Sanctis et al., 2016; Quick et al., 2019).

The crater is dated at ∼22 My and the internal lobate deposits are contemporaneous within the error of the model ages, when using the lunar-derived chronology model

Facula ages are more difficult to constrain because of their small area. Their brightness suggests a recent emplacement since micrometeorites tend to darken surface material on timescales of a few My

Upon being emplaced in Ceres' zero-pressure surface environment, these brines would have subsequently boiled, launching vapor, ice, and salt particles on ballistic trajectories. The buildup of these salts could have formed the faculae. It is also possible that the faculae were formed when fractures containing salty liquids and <2 wt % of a volatile constituent such as water vapor, CH4, CO2, or NH3 intersected with Ceres' surface. Upon reaching the surface, volatiles in solution would have exsolved, causing eruptive boiling and resulting in salt particles being launched on ballistic trajectories that were wide enough to create the faculae

brine fountaining” was the most plausible explanation for the formation of the faculae. During this process, briny liquid extruded onto the surface, followed by flash freezing of carbonate and ice particles, particle fallback, and finally, sublimation of any residual ice.

Diurnal variations of Occator's Cerealia Facula (the central bright deposit) were initially interpreted as a signature of haze (i.e., water vapor lifting small particles) (Thangjam et al., 2016); however, no evidence has been found in data from the VIR instrument for the presence of water ice within Occator (De Sanctis et al., 2016). The nature of these brightness variations is currently being studied.

There are two lines of evidence for the existence of liquid in Ceres at present. First, the global relaxation of topographical features ≥250 km was interpreted by Fu et al. (2017) as evidence for the presence of a weak layer below the crust, that is, in the upper mantle. From the viscosity constraint <1021 Pa s, Fu et al. inferred that the weak layer should contain a small fraction of pore fluids in a matrix of phyllosilicates. Modeling cannot provide a more specific range about the thickness or viscosity of that inferred weak layer except that it extends at least 60 km into the mantle (Fu et al., 2017) (Fig. 2). Hence, these geophysical models are currently not efficient to distinguish between the interior models of Travis et al. (2018; “mudball” mantle†) and Castillo-Rogez and McCord (2010; more compact mantle).

Clathrates have the same density as ice but their thermal conductivity is at least one order of magnitude less and their viscosity at least three orders of magnitude greater than ice at the same temperature. Hence, they are the most likely compound responsible for Ceres' low-density and high-strength crust (Section 3.2). Porosity can also contribute to decreasing thermal conductivity but tends to weaken the crust and is thus expected to be limited in extent and likely in the form of macroporosity (i.e., local), as indicated by the high number of polygonal craters (Otto et al., 2016). While the porous medium suggested by Fu et al. (2017) does not meet the general definition of “ocean” as a vast layer of water, it could be a medium analogous (at least physically) to the pelagic environment of Earth's deep ocean in terms of pressure, but at colder temperatures. The temperature of that layer may be subzero, set by the eutectic temperature of remnant brines (Castillo-Rogez et al., 2019a) or much warmer owing to slow heat loss (Travis et al., 2018). The mantle porosity governs the extent of the interface at which liquid water and rock can interact, that is, where chemical gradients can arise and bioessential species may become concentrated. Porosity could also have developed due to fracturing of a cohesive mantle during evolution. Neveu et al. (2015) showed that thermal stresses due to cooling could lead to pervasive cracking down to the center of Ceres.

Evidence for recent geological activity has been most recently interpreted as resulting from three possible interior settings. In the setting described by Travis et al. (2018), thermal convection in a long-lived ocean triggers convective upwelling in the crust, which would be responsible for the observed domes. On Europa, the existence, spacing, and morphology of pits, spots, and domes have long been used to infer locations of enhanced local heating and the possibility of local liquid pockets in the ice shell (e.g., Pappalardo et al., 1998; Michaut and Manga, 2014). Recent work has also suggested that some of Europa's domes may have formed from eruptions of briny cryolava in areas of enhanced local heating (Quick et al., 2017).

Diapirism offers another possible mechanism for material extrusion. The resemblance of Occator to lunar floor-fractured craters and the fractured surfaces of the Cerealia Dome might suggest formation by ascending diapirs (Buczkowski et al., 2018a, 2018b; 2019). Ruesch et al. (2019b) considered several possible formation mechanisms for the faculae and concluded that brine extrusion from a vertical conduit, followed by flash freezing of ice, ejection of bright particles, and subsequent sublimation of any extruded liquids, was the most likely formation mechanism. Further modeling of the migration of briny fluids in vertical conduits, and the subsequent eruption of these fluids at Ceres' surface by Quick et al. (2019), confirmed that these processes were able to produce Occator's faculae. The emplacement of the large Ahuna Mons also seems to be best explained by the diapirism of a slurry of brine and silicate particles that Ruesch et al. (2019a) connect to the top of the mantle.

ccording to Ruiz et al. (2007), diapirs themselves could create transient habitable zones and/or reactivate dormant ones by warming the surrounding ice for hundreds of thousands of years. The same could be said for sills and fractures containing briny cryomagmas. However, more detailed investigation is needed to assess whether brine pockets could offer a propitious environment for halophiles (based on temperature and water activity, both of which are poorly constrained.) Neveu and Desch (2015) suggested that compressive stresses in a freezing brine reservoir could drive the upwelling of liquid/soft material in recent history. Recently, Quick et al. (2019) modeled this process and found it to be a viable means of transporting briny liquids to Occator's central region.

Finally, impact-produced heating could be responsible for producing local melt pool, as suggested below Occator's floor (Bowling et al., 2019). Hesse and Castillo-Rogez (2019) suggested that reservoir could last up to ∼10 My. Other large craters also display carbonates and other salts associated with fractures (e.g., Dantu crater; Stephan et al., 2018), suggesting that impact-produced melt was a common process on Ceres. Impact heating could also warm up the crust and drive solid-state convection arising from differential loading following impacts into a heterogeneous, icy crust (Bland et al., 2019). The mixture of ammoniated clays, serpentine, and Mg/Ca carbonate is best explained by alteration in the presence of abundant water (water to rock ratio ≥2), a pH around 9–11, and a partial pressure of hydrogen log (PH2) > −6 rogressive freezing of Ceres' ocean would increase its salinity. The residual liquid would become enriched in ammonia and chlorides (NaCl and KCl) with a pH equal to 7.5 (Castillo-Rogez et al., 2018) and a eutectic temperature of 210 K. Thermal modeling shows that Ceres could preserve warmer temperatures at the base of the crust, >255 K until present day (Neveu et al., 2015; Travis et al., 2018; Castillo-Rogez et al., 2019a).

Ahuna Mons is an ∼4-km-high and ∼21-km-wide mountain that is interpreted as a viscous cryovolcanic dome formed by the ascent of cryomagma from the depth and subsequent eruption onto the surface in a manner akin to lava dome emplacement on Venus and Europa

Dawn's observations confirmed earlier predictions for a volatile-rich crust encompassing the bulk of a former ocean, now frozen, and provide hints for a weak interior that may reflect the presence of a relict liquid layer or brine pockets. These observations led to Ceres' classification as a “candidate” ocean world in the ROW (Hendrix et al., 2019). Current knowledge indicates that Ceres once had water, organic building blocks for life, energy sources, and redox gradients, and perhaps still does today. Perhaps more importantly, Ceres' astrobiological value comes from its potential for continuous habitability, commencing directly after accretion with a global ocean in which advanced chemical differentiation developed.

This global ocean could have been maintained for billions of years (Travis et al., 2018). Most of Ceres' surface properties record the consequences of that early period, while contemporary activity is evident in a few places. However, as per its size and water abundance, Ceres belongs to a class of objects that could host a high fugacity of hydrogen, organic molecules, and alkaline conditions, as was suggested for Europa (e.g., McKinnon and Zolensky, 2003) and inferred from Cassini observations of Enceladus (Postberg et al., 2011; Marion et al., 2012).

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1002/2017JE005335

Spectroscopic observations of high-albedo spots on Ceres have confirmed that at least some of these nonpermanently shadowed areas have a water ice component (Combe et al., 2016). The strength of the water absorption band varies from area to area, and not all high-albedo areas on Ceres contain water ice. For example, the Occator high-albedo material has no water absorption signature and instead has absorption signatures consistent with carbonate and ammonium salts (De Sanctis et al., 2016). Recent work suggests that exposed surface ice is not present equatorward of ~30° latitude (Combe et al., 2017). One possible cause of the dearth of water ice patch detections in the ~ ± 30° latitude region could be that a sublimation lag has caused them to lose their distinctive high-albedo and near-IR absorption features and are therefore nearly impossible to detect

We have shown that short-lived local water ice exposure can explain the transient exosphere detections by Küppers et al. (2014). We cannot rule out a global excess buried ice table producing some amount of background vapor but that background vapor flux alone is not sufficient to explain the Küppers et al. (2014) observation.

We determined that conditions most favorable for the production of water vapor at a rate of > ~1 kg s�1 correspond to surface ice remaining optically bright (less than one monolayer of regolith particles) for less than a few terrestrial years or, depending on the regolith content of the ice, significantly shorter amounts of time. This means that Dawn observing a single exposure of water ice that could have been the source of the Küppers et al. (2014) observation is most likely impossible, as the ice patch would have totally faded before the spacecraft’s March 2015 arrival (an interval of approximately two terrestrial years after the last reported detection of water vapor in March 2013 by Küppers et al., 2014) in all but the purest ice case we tested. These quick-fading lifetimes for water ice patches that could match the Küppers et al. (2014) vapor output rate are consistent with the transient nature of the water vapor exosphere detections, even with significant sublimation occurring several times longer than the fading lifetime of the water ice patch. Strong diurnal and seasonal variations in vapor production that the model predicts are consistent with the temporal variations reported by Küppers et al. (2014).

Particles lofted by water vapor escaping from the surface of ice exposures are generally small, on the order of tenths of microns or less, and so this represents an ineffective mechanism for prolonging the visible lifetime of water ice patches unless Ceres has finer-grained regolith than other airless bodies.

https://www.nature.com/articles/s41550-020-1019-1

he gravity and shape data acquired by the Dawn spacecraft during its primary mission revealed that Ceres is partially differentiated with an interior structure consistent with a volatile-rich crust, a mantle of hydrated rock and isostatically compensated topography1,2,3. Detailed analyses showed that the mechanically strong crust overlays a weak, fluid-bearing upper mantle4. Previous studies, however, assumed that Ceres’s crust is a uniform layer. Here, we report findings from the new high-resolution gravity data from Dawn’s second extended mission (XM2), which reveal a complex crustal structure of Ceres. In the low-altitude regions probed by the Dawn spacecraft during the XM2 phase, we observe that gravity–topography admittance progressively shifts to a lower density solution at higher degrees, implying a radial density gradient across Ceres’s crust that is consistent with decreasing porosity with depth and/or increasing content of dense phases, such as rock and salts. That gradient brings a critical new constraint on the crustal freezing history, suggesting that the salts and silicates concentrated in the liquid phase while the crust was growing. Localized spectral analysis of the new data also shows evidence for a lower crustal density in the north polar region than in the south or near the equator, supporting impact-driven porosity variations for the observed latitudinal density differences5. On the local scale, the new data show evidence for density or rheological variations within the crust, in association with lobate landslides and ejecta deposits that were inferred to be ice-rich6,7 as well as an extensional fault system8. These inferences provide geophysical context for geological features on the surface and help us advance our understanding of the evolution of an ice-rich but heat-starved body, whose evolution was in part shaped by impacts.

http://planetary.brown.edu/pdfs/5318.pdf

The Dawn team spent over 2 yr evaluating the character of its dark surface (Russell et al. 2016) and has documented the pervasive presence of Mg-serpentine, ammoniated clays, and opaques (De Sanctis et al. 2015; Ammannito et al. 2016) as well as notable unusual deposits of exceptionally bright carbonates within Occator crater

the unmistakable absorption signature at 3.4 lm of organic materials was also identified in the northern hemisphere of Ceres

Currently, all but one small area identified to be organic-rich (by the presence of a prominent 3.4 lm absorption band) occur in this region. (the coniraya quadrangle)

With only one apparent exception, all of the ROR areas are found across a ~200 km elongated region on northern Ceres shown in Fig. 1A. Except for the cluster of ROR areas near Ernutet (including related talus movement down slopes), most occurrences of ROR materials are widely separated, discrete, and quite small. A few instances suggest possible directionality,

With only one apparent exception, all of the ROR areas are found across a ~200 km elongated region on northern Ceres shown in Fig. 1A. Except for the cluster of ROR areas near Ernutet (including related talus movement down slopes), most occurrences of ROR materials are widely separated, discrete, and quite small. A few instances suggest possible directionality,

Note that while the lower panels involving preexisting ROR material (B and D) would most likely represent products of endogenic processes on Ceres, they could also conceivably represent ancient ROR deposits from a major impact with an organic-rich body

http://hosting.astro.cornell.edu/academics/courses/astro2202/BrinyCeres.pdf

Recent emplacement of bright deposits sourced from brines attests to Ceres being a persistently geologically active world, but the surprising longevity of this activity at the 92-km Occator crater has yet to be explained. Here, we use new high-resolution Dawn gravity data to study the subsurface architecture of the region surrounding Occator crater, which hosts extensive young bright carbonate deposits (faculae). Gravity data and thermal modelling imply an extensive deep brine reservoir beneath Occator, which we argue could have been mobilized by the heating and deep fracturing associated with the Occator impact, leading to long-lived extrusion of brines and formation of the faculae. Moreover, we find that pre-existing tectonic cracks may provide pathways for deep brines to migrate within the crust, extending the regions affected by impacts and creating compositional heterogeneity. The long-lived hydrological system resulting from the impact might also occur for large impacts in icy moons, with implications for creation of transient habitable niches over time.

Ceres’s history as revealed by Dawn provides an exemplar for understanding the evolution of icy bodies that partially or completely differentiated. The deep compositional heterogeneity inferred from its density structure, which may reflect interior convection or regional variations in mantle temperature and brine content, may be applicable to other bodies with mostly frozen silicate-rich interiors, such as Charon. The role of impacts in mobilizing oceanic materials that spill onto the surface has been demonstrated for this dwarf planet that bears many similarities to icy moons, indicating that large impacts in icy shells, especially if they are relatively thin (a few tens of kilometres, such as Europa), could connect a subsurface ocean to a local melt chamber. In addition, injection of ocean material into impact-induced fractures could generate crustal heterogeneities in any body that had an ocean phase during its evolution. Impact simulations25 indicate a substantial fraction of the impactor may be retained in the melt chamber. The geochemical characteristics of the resulting reservoir, which combines a crustal component, oceanic component and exogenic material, could have important implications for astrobiology28. Comparison with data returned by the upcoming Europa Clipper and Jupiter Icy Moons Explorer (JUICE) missions will further our understanding of the role of impact-produced heat and damage in driving local geological activity and introducing heterogeneities in icy crusts.

To better understand the contribution of impacts to the evolution of Ceres’s crust, the final phase of the Dawn mission (second extended mission, XM2) was designed to investigate the ~20-Myr-old Occator crater2 at a spatial resolution ten times better than achieved during the prime mission. In XM2, the spacecraft achieved a minimum altitude below 35 km over Occator crater (20o N, 120o W), imaging most of the crater at resolution of 3.3–10m pixel−1 , and increasing spatial sampling of all other instruments. In particular, it yielded gravity variations

https://www.nature.com/articles/s41467-020-15973-8

Before acquiring highest-resolution data of Ceres, questions remained about the emplacement mechanism and source of Occator crater’s bright faculae. Here we report that brine effusion emplaced the faculae in a brine-limited, impact-induced hydrothermal system. Impact-derived fracturing enabled brines to reach the surface. The central faculae, Cerealia and Pasola Facula, postdate the central pit, and were primarily sourced from an impact-induced melt chamber, with some contribution from a deeper, pre-existing brine reservoir. Vinalia Faculae, in the crater floor, were sourced from the laterally extensive deep reservoir only. Vinalia Faculae are comparatively thinner and display greater ballistic emplacement than the central faculae because the deep reservoir brines took a longer path to the surface and contained more gas than the shallower impact-induced melt chamber brines. Impact-derived fractures providing conduits, and mixing of impact-induced melt with deeper endogenic brines, could also allow oceanic material to reach the surfaces of other large icy bodies.

Ceres likely formed > 3 Myr and < 5 Myr after CAIs6 and is partially differentiated into a rocky interior and a comparatively more volatile-rich crust1, which is composed of rock, salts, clathrates, and <––––40% water ice7,8. An ancient subsurface Cerean ocean would have frozen early in the dwarf planet’s evolution, and remnants of this ancient ocean could still exist as subsurface brine pockets at the base of the crust6,7,9. In general, Ceres’ surface is ubiquitously covered by phyllosilicates10. In addition, Ceres displays some exceptional areas, such as Occator crater. Occator is a 92-km diameter complex crater and is one of the most well-known features on Ceres’ surface because of its enigmatic bright deposits, called faculae1,11,12,13. Cerealia Facula is the central bright region, mostly located in Occator’s central pit. The central pit also contains a dome named Cerealia Tholus. Pasola Facula is a bright deposit located on a ledge above the central pit, while Vinalia Faculae are in the eastern crater floor (Figs. 1a and 2a). The faculae are up to 6 times brighter than Ceres’ average material, as defined by ref. 14. They are mostly composed of sodium carbonate and ammonium chloride, consistent with the remnants of brines sourced in the subsurface that lost their liquid water component on Ceres’ surface15,16. Hydrous sodium chloride has also been observed within Cerealia Facula and, because of its rapid dehydration timescales at Ceres’ surface conditions (tens of years), suggests that at least some brines may still be present in the subsurface17.

https://agupubs.onlinelibrary.wiley.com/doi/pdfdirect/10.1002/2016GL071652

the surface composition of Ceres is dominated by a mixture of ammoniated phyllosilicates, Mg-phyllosilicates, and carbonates [De Sanctis et al., 2015]. A dark spectrally neutral material causes the overall low albedo of Ceres surface material [De Sanctis et al., 2015]. The composition has been found to be rather homogeneous on a global scale implying a globally widespread endogenous formation of the surface material, i.e., an aqueous alteration of silicates [Ammannito et al., 2016]. In contrast, the abundance of the individual surface compounds appears to be variable, which has been interpreted as evidence for a vertically stratified upper crust [Ammannito et al., 2016]. The VIR-derived composition, however, does not explain c

https://agupubs.onlinelibrary.wiley.com/doi/pdfdirect/10.1002/2016GL069368

Ceres has only a small spin axis tilt (4∘), and craters near its rotational poles can experience permanent shadow and trap volatiles, as is the case on Mercury and on Earth’s Moon. Topography derived from stereo imaging by the Dawn spacecraft is used to calculate direct solar irradiance that defines the extent of the permanently shadowed regions (PSRs). In the northern polar region, PSRs cover ∼1800 km2 or 0.13% of the hemisphere, and most of the PSRs are cold enough to trap water ice over geological time periods. Based on modeling of the water exosphere, water molecules seasonally reside around the winter pole and ultimately an estimated 0.14% of molecules get trapped. Even for the lowest estimates of the amount of available water, this predicts accumulation rates in excess of loss rates, and hence, there should be fresh ice deposits in the cold traps.

https://www.sciencedirect.com/science/article/abs/pii/S0012821X17304405

Preferential attenuation of long wavelength topography (≥150 km) on Ceres suggests that the viscosity of its crust decreases with increasing depth.

We infer that Ceres has a mechanically strong crust with maximum effective viscosity ∼1025 Pa s. Combined with density constraints, this rheology suggests a crustal composition of carbonates or phyllosilicates, water ice, and at least 30 volume percent (vol.%) low-density, high-strength phases most consistent with salt and/or clathrate hydrates.

The inference of these crustal materials supports the past existence of a global ocean, consistent with the observed surface composition. Meanwhile, we infer that the uppermost ≥60 km of the silicate-rich mantle is mechanically weak with viscosity <1021 Pa s, suggesting the presence of liquid pore fluids in this region and a low temperature history that avoided igneous differentiation due to late accretion or efficient heat loss through hydrothermal processes.

https://authors.library.caltech.edu/72179/3/14/science.aah6765.DC1/Prettyman.SM.pdf

In contrast, the C contribution to the 4.4 MeV peak is over a factor of two higher at Ceres than at Vesta. Despite exogenic contamination by carbonaceous impactors, the C content of Vesta’s regolith is small (< 0.1 wt.% if the H measured by GRaND was delivered by impactors with CM chondrite composition). Therefore, C contributions to the 4.4 MeV peak at Vesta must be caused by the interaction of neutrons made in Vesta’s regolith with GRaND’s carbon-composite housing. That the C contribution to 4.4 MeV peak increases at Ceres, despite a large reduction in the flux of interrogating fast neutrons, is evidence for elevated [C] in Ceres regolith. However, unknown backgrounds from neutrons impinging on GRaND’s C-rich housing complicate quantification of [C] using gamma rays. Equatorial fast and thermal + epithermal neutron counting rates (for pixels withi

https://www.sciencedirect.com/science/article/abs/pii/S0019103521000415

Cerean crater morphologic types and simple-complex transition diameters are smaller than on Vesta but similar to those on icy satellites, indicating a much weaker rheology for Ceres' outer layers under impact conditions. These are consistent with geophysical indications of a low-density water ice and probably clathrate rich outer shell. Fluidized floor deposits (impact melt or melt-solid mixtures) are significant in craters >25 km across on Ceres but absent on Saturn satellites. Central pit craters are common on Ceres (at diameters of ~75 to 150 km consistent with gravity scaling from the larger Galilean satellites) but are absent on Saturnian satellites and Charon.

https://www.sciencedirect.com/science/article/abs/pii/S0019103517303342

Disk-integrated telescopic spectral observations indicated that Ceres’ surface is hydroxylated, similar to but not exactly the same as some of the carbonaceous chondrite classes of meteorites. Furthermore, Ceres’ bulk density is low, suggesting significant water content. The Dawn mission in orbit around Ceres provided a new and much larger set of observations on the mineralogy, molecular and elemental composition, and their distributions in association with surface features and geology. The set of articles contained in this special issue is the first treatment of the entire surface composition of Ceres using the complete High Altitude Mapping Orbit (HAMO) Dawn Ceres data set and the calibrations from all the Dawn instruments. Most articles here treat the different geologic quadrangles of Ceres within the context of the entire body. There also are articles that treat global or technical topics. As a whole, these articles provide a current and comprehensive view of Ceres’ surface composition. Ceres’ surface composition shows a fairly uniform and widespread distribution of NH4- and Mg-phyllosilicates and carbonates, mixed with a dark component and with some exposures of salts and water-ice on Ceres’ surface, all indicative of the presence of aqueous alteration processes that involved the entire dwarf planet. There is also likely some contamination by low velocity infall, as seen on Vesta, but it is more difficult to distinguish this infall from native Ceres material, unlike for the Vesta case. This article introduces and provides the context for the following papers, presents a summary of the various findings, and integrates them into some general conclusions.

https://www.nature.com/articles/s41467-020-15973-8

Before acquiring highest-resolution data of Ceres, questions remained about the emplacement mechanism and source of Occator crater’s bright faculae. Here we report that brine effusion emplaced the faculae in a brine-limited, impact-induced hydrothermal system. Impact-derived fracturing enabled brines to reach the surface. The central faculae, Cerealia and Pasola Facula, postdate the central pit, and were primarily sourced from an impact-induced melt chamber, with some contribution from a deeper, pre-existing brine reservoir. Vinalia Faculae, in the crater floor, were sourced from the laterally extensive deep reservoir only. Vinalia Faculae are comparatively thinner and display greater ballistic emplacement than the central faculae because the deep reservoir brines took a longer path to the surface and contained more gas than the shallower impact-induced melt chamber brines. Impact-derived fractures providing conduits, and mixing of impact-induced melt with deeper endogenic brines, could also allow oceanic material to reach the surfaces of other large icy bodies.

Ceres likely formed > 3 Myr and < 5 Myr after CAIs6 and is partially differentiated into a rocky interior and a comparatively more volatile-rich crust1, which is composed of rock, salts, clathrates, and <––––40% water ice7,8. An ancient subsurface Cerean ocean would have frozen early in the dwarf planet’s evolution, and remnants of this ancient ocean could still exist as subsurface brine pockets at the base of the crust6,7,9. In general, Ceres’ surface is ubiquitously covered by phyllosilicates10. In addition, Ceres displays some exceptional areas, such as Occator crater. Occator is a 92-km diameter complex crater and is one of the most well-known features on Ceres’ surface because of its enigmatic bright deposits, called faculae1,11,12,13. Cerealia Facula is the central bright region, mostly located in Occator’s central pit. The central pit also contains a dome named Cerealia Tholus. Pasola Facula is a bright deposit located on a ledge above the central pit, while Vinalia Faculae are in the eastern crater floor (Figs. 1a and 2a). The faculae are up to 6 times brighter than Ceres’ average material, as defined by ref. 14. They are mostly composed of sodium carbonate and ammonium chloride, consistent with the remnants of brines sourced in the subsurface that lost their liquid water component on Ceres’ surface15,16. Hydrous sodium chloride has also been observed within Cerealia Facula and, because of its rapid dehydration timescales at Ceres’ surface conditions (tens of years), suggests that at least some brines may still be present in the subsurface17.

The faculae are up to 6 times brighter than Ceres’ average material, as defined by ref. 14. They are mostly composed of sodium carbonate and ammonium chloride, consistent with the remnants of brines sourced in the subsurface that lost their liquid water component on Ceres’ surface15,16. Hydrous sodium chloride has also been observed within Cerealia Facula and, because of its rapid dehydration timescales at Ceres’ surface conditions (tens of years), suggests that at least some brines may still be present in the subsurface17.

Flows are hypothesized to have emplaced the bright material that has a more continuous appearance (corresponding to the continuous bright material geologic unit), while the discontinuous bright material, which is comparatively diffuse, was suggested to have been ballistically emplaced

almost the entire crater interior is coated by lobate material, which has been interpreted to have been emplaced as a slurry of impact-melted water, salts in solution and blocks of unmelted silicates and salts flowed around the crater interior shortly after Occator’s formation18 (“Methods”, subsection “Lobate material”). While the composition of the melted material is different (water ice versus silicate rock), Occator’s lobate material is the Cerean equivalent of crater-fill impact melt

The distribution of the faint mottled bright material around Occator’s central pit is analogous to the uneven distribution of mounds, which are interpreted to be hydrothermal, around the central structure of the martian crater Toro

that pathways to the surface for the faculae-forming brines were likely opened by the prevalent impact-induced fracturing throughout the crater30. Moreover, excess pressures from partial crystallization of the melt chamber could also initiate and sustain fracturing

the Occator-forming impact would have created a hydrothermal system on water-ice-rich Ceres32, and previous work found that the morphology of Cerealia Facula is generally consistent with terrestrial, mostly non-impact-generated, hydrothermal deposits

terrestrial hydrothermal springs occur at ambient temperatures33. Moreover, salts are precipitated from cold springs in the Canadian Arctic that are around or below 0 °C

Vinalia Faculae are associated with a prominent set of fractures, from which the faculae-forming brines were proposed to originate19,21,36,37,38. However, our XM2-based geologic mapping reveals that these fractures cut through the Vinalia Faculae. Reactivated later?

Only a relatively small force is required to fracture Ceres's crust

Vinalia Faculae could be sourced from a deep, long-lived brine reservoir, which has been suggested to be present at the base of the crust (~35-km deep) on the basis of topographic analyses7 and is supported by thermal modeling9. This deep brine reservoir would have existed prior to the Occator-forming impact and is inferred to be present on a global scale7,9,30, although the amount of liquid may vary laterally9 (Fig. 5). The impact-induced melt chamber would likely thermally connect to this deep brine reservoir30,49. Therefore, the central-faculae-forming brines primarily originated from the impact-induced melt chamber, with likely long-term contributions from the deep brine reservoir, while the Vinalia-Faculae-forming brines only originated from the deep brine reservoir.

A set of crater-count-derived model ages suggest that Cerealia Facula began to form ~8 million years ago, while formation of Vinalia Faculae began ~4 million years ago

https://earthsky.org/space/flowing-water-on-vesta

imagine an asteroid collision, and the slow-motion excavation of a crater (slow because of the relatively low gravity), and the impact shock flashing an icy deposit into water, and it springing and tumbling down the slumping wall of the crater mixed with the cascading debris of the crater wall, the surface steaming all the way (because it’s in a vacuum), all of this silent (because it’s in a vacuum), the debris filling the new crater’s floor, still steaming at the top while freezing toward the bottom. Periodically, rarely, a hole appears in the floor, sediment draining downward, as escaping vapor leaves a void behind.

https://agupubs.onlinelibrary.wiley.com/doi/pdfdirect/10.1002/2017JE005302

Ceres is the largest body in the asteroid belt. Unlike most of the objects in that region of the solar system, Ceres has a round shape due to its sufficient gravity. Little was known about Ceres before the Dawn mission. The measurements by the Dawn spacecraft allowed precise determination of Ceres’ shape and gravity field. We use these two data sets to understand its internal structure. It was predicted in the past that Ceres topography would quickly viscously relax if Ceres had an icy crust. We find only a modest evidence of viscous relaxation, which implies that Ceres’ crust is much stronger than water ice. We also find that Ceres topography is isostatically compensated. That is, much like with a floating iceberg, the weight of mountains is compensated by a displaced volume of the underlying mantle. Such a simple model explains most of Ceres’ gravity anomalies. However, some gravity anomalies remain unaccounted for. For example, we find evidence for a mass concentration analogous to those in lunar maria in the two biggest impact basins. A strong negative anomaly is observed around Occator— the famous bright spot crater. A strong positive anomaly is centered at Ahuna Mons—a unique pyramid-shaped mountain. The globally averaged crustal density that we find is rather low. Remarkably, Ceres crust is made out of a strong, rock-like material that, however, has a density much lower than that of rocks. This implies that Ceres’ crust contains a lot of salts and clathrates, which are strong and light materials.

McCord and Sotin (2005) estimate that Ceres has from 17% to 27% of nonmineralogically bound water by mass. In this respect, Ceres is similar to icy satellites or even trans-Neptunian objects

https://hal.archives-ouvertes.fr/hal-02961029/document

Similarly, ammonium-bearing minerals are ubiquitous on the surface of Ceres, even though they show a difference in abundance and in chemical form (De Sanctis et al. 2016; Ammannito et al. 2016). The observed mineralogy requires pervasive and long-standing aqueous alteration (De Sanctis et al. 2016; Ammannito et al. 2016), as also suggested by the spatial uniformity of element abundance measurements of equatorial regolith (Prettyman et al. 2016; Lawrence et al. 2018). The global map of hydrogen abundance obtained by GRaND indicates the presence of ice buried below the Cerean regolith, which is increasingly abundant moving away from the equator to high latitudes (Prettyman et al. 2016; Lawrence et al. 2018).

https://www.jpl.nasa.gov/images/ceres-internal-structure-artists-concept

Using information about Ceres' gravity and topography, scientists found that Ceres is "differentiated," which means that it has compositionally distinct layers at different depths. The most internal layer, the "mantle" is dominated by hydrated rocks, like clays. The external layer, the 24.85-mile (40-kilometer) thick crust, is a mixture of ice, salts, and hydrated minerals. Between the two is a layer that may contain a little bit of liquid rich in salts, called brine. It extends down at least 62 miles (100 kilometers). The Dawn observations cannot "see" below about 62 miles (100 kilometers) in depth. Hence, it is not possible to tell if Ceres' deep interior contains more liquid or a core of dense material rich in metal.

https://www.sciencedirect.com/science/article/abs/pii/S0019103517306218

Vinalia and Cerealia Faculae are bright and salt-rich localized areas in Occator crater on Ceres. The predominance of the near-infrared signature of sodium carbonate on these surfaces suggests their original material was a brine. Here we analyze Dawn Framing Camera's images and characterize the surfaces as composed of a central structure, either a possible depression (Vinalia) or a central dome (Cerealia), and a discontinuous mantling. We consider three materials enabling the ascent and formation of the faculae: ice ascent with sublimation and carbonate particle lofting, pure gas emission entraining carbonate particles, and brine extrusion. We find that a mechanism explaining the entire range of morphologies, topographies, as well as the common composition of the deposits is brine fountaining. This process consists of briny liquid extrusion, followed by flash freezing of carbonate and ice particles, particle fallback, and sublimation. Subsequent increase in briny liquid viscosity leads to doming. Dawn observations did not detect currently active water plumes, indicating the frequency of such extrusions is longer than years.

https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2018GL081473

Simulations indicate Ceres should preserve a warm crust until present if the crust is rich in clathrate hydrates. The temperature computed at the base of the crust exceeds 220 K for a broad range of conditions, allowing for the preservation of a small amount of brines at the base of the crust. However, a temperature ≥250 K, for which at least 1 wt.% sodium carbonate gets in solution requires a crustal abundance of clathrate hydrates greater than 55 vol.%, a situation possible for a narrow set of evolutionary scenarios.

A key feature to be reproduced is the long‐term persistence of liquid below the crust, at about 40 km depth, as suggested by the observed topography. The possibility for the occurrence of liquid in Ceres at present depends on the presence of insulating material in the crust, for example, in the form of gas hydrates.

This corresponds to a water to rock ratio of 47:53 in volume or 25:75 in mass, simply assuming all the water is in the form of ice and rock is anhydrous. Hence, Ceres' evolution is driven by the interplay of radiogenic heating with the thermodynamic and mechanical properties of water ice and hydrated minerals.

Gravity data yielded a normalized mean moment of inertia of about 0.37 pointing to partial differentiation (Park et al., 2016). Admittance analysis provided additional constraints on crustal properties, which is 40 km thick on average with a density of 1,200 to 1,400 kg/m3 (assuming a two layer model, Ermakov et al., 2017). The crust overlays a mantle with a density of ∼2,400 kg/m3 and a viscosity lower than 1021 Pa s, which Fu et al. (2017) interpreted as evidence for a small amount of pore fluid. The nature of the fluid is not constrained but it could realistically be sodium and potassium chloride brines as suggested by geochemical modeling (Castillo‐Rogez et al., 2018; Neveu & Desch, 2015). The brines likely correspond to residual liquid from the freezing of a global ocean suggested in Ceres early on (Ammannito et al., 2016; Castillo‐Rogez & McCord, 2010). The eutectic temperature of that brine could be as low as about 220 K (Castillo‐Rogez et al., 2018). Ammonia could also be present and decrease the eutectic further. However, the widespread occurrence of ammonium both in the form of clays and salts on Ceres' surface indicates these formed in an environment where ammonia was a minor component. Following Le Chatelier's Principle, most of the ammonia should be turned into ammonium since the latter was removed from the medium, either by exchange with cations in clays or by salt precipitation.

Brines are believed to play a role in the emplacement of two outstanding geological landmarks: Ahuna Mons (Ruesch et al., 2016) and the bright material (faculae) in Occator crater (De Sanctis et al., 2016; Quick et al., 2019). Both constructs display sodium carbonate (De Sanctis et al., 2016, for the Occator faculae and Zambon et al., 2017, for Ahuna Mons). The deep brine layer identified by Fu et al. (2017) has been suggested as a reservoir for the Occator faculae (Quick et al., 2019).

Additional constraints on Ceres' crustal composition come from its mechanical strength, which Bland et al. (2016) found to be at least three orders of magnitude greater than water ice for Ceres' temperatures. It suggests no more than 40 vol.% of a weak phase, which Bland et al. (2016) interpreted as an upper bound on the water ice fraction. That fraction could be less if the crust also contains void porosity. The extent of porosity is not constrained though and might show lateral variations, as indicated by the distribution of surface fractures (Scully et al., 2017). Strong phases are required to reproduce the strength of the crust, which Fu et al. (2017) inferred to be a mixture of phyllosilicates, salt hydrates, and gas hydrates (i.e., clathrate hydrates). The latter are likely to be mixed methane and carbon dioxide hydrates (Castillo‐Rogez et al., 2018) with a density of about 1,000 kg/m3 (Waite et al., 2007). Geochemical modeling suggests there should be no more than 20 vol.% salts in the crust and the averaged density of these salts, composed of carbonates and chlorides, is about 2,200 kg/m3 (Castillo‐Rogez et al., 2018). In this framework, phyllosilicates are a mixture of magnesium serpentine and clays, consistent with surface composition (De Sanctis et al., 2018). A mixture of 10 vol.% silicates, 20 vol.% hydrated salts, and 30 vol.% ice and 40 vol.% clathrates matches the average crustal density derived by Ermakov et al. (2017) and is consistent with the strength estimates from Bland et al. (2016) and Fu et al. (2017).

Ceres' crust relaxes on scales greater than ∼250 km, which Fu et al. (2017) interpreted with a crustal viscosity profile decreasing by one order of magnitude every 10 km. Formisano et al. (2018) used a 2‐D finite element numerical code to solve the thermal convection equations in the Boussinesq approximation and explored the onset of subsolidus thermal convection in Ceres' crust. They found that no thermal convection is possible, assuming less than 40 vol.% of weak material. Convection may be possible if the ice content is slightly greater than 40% and the temperature at the base of the crust ranges from 250 to 300 K. Strong thermal convection is possible if 50 vol.% of ice is assumed, leading to a Rayleigh number greater than 108. However, as shown below, the modeled temperatures at the base of the crust are expected to be colder than required for convection to be initiated throughout Ceres' history. Hence we assume heat is transferred by conduction in Ceres' crust.

https://onlinelibrary.wiley.com/doi/full/10.1111/maps.12138

the surface of Vesta exhibits absorption features indicative of basaltic minerals, similar in composition to the howardite–eucrite–diogenite (HED) family of basaltic achondrite meteorites. This indicated that Vesta must have been molten and probably differentiated. NASA's Dawn spacecraft observed Vesta from orbit for slightly more than a year (Russell et al. 2012) with a suite of three instruments: a visible and infrared spectrometer—VIR (De Sanctis et al. 2011a), two redundant Framing Cameras—FC (Sierks et al. 2011), and a gamma ray and neutron detector—GRaND (Prettyman et al. 2012). The Dawn spacecraft permitted detailed study of Vesta's basaltic surface by VIR (De Sanctis et al. 2012a), and together with the other instruments, confirmed that Vesta has experienced planetary‐scale differentiation that produced a crust, mantle, and a core (Russell et al. 2012). Our knowledge of Vesta has been vastly increased by Dawn's brief stay.

https://www.nature.com/news/dawn-spacecraft-finds-signs-of-water-on-vesta-1.11457

Vesta has a water cycle; asteroids deposit water in Vesta's soil, and then expose it in subsequent impacts. These impacts cause water to erupt, leaving pits, some 200m deep.

https://www.sciencedirect.com/science/article/abs/pii/S0012821X20300121

exogenic delivery of aliphatic organics is inefficient, as most of the spectral signature of the organic species would be thermally degraded and diluted by mixing with target material in the ejecta blanket of a given crater.

https://cosmosmagazine.com/space/ceres-lonely-ice-volcano-was-once-one-of-many/#:~:text=The%20dwarf%20planet%20Ceres%20has,peak%20known%20as%20Ahuna%20Mons

Only one volcano (Ahuna mons) but up to 22 may have formed and then relaxed back into the surface (about once every 50 million years).

https://www.nature.com/articles/s41550-020-1146-8

NASA’s Dawn mission revealed a partially differentiated Ceres that has experienced cryovolcanic activity throughout its history up to the recent past. The Occator impact crater, which formed ~22 Myr ago, displays bright deposits (faculae) across its floor whose origins are still under debate: two competing hypotheses involve eruption of brines from the crust–mantle transition boundary (remnants of an ancient ocean) or alternatively from a shallow impact melt chamber. Here we report new constraints on the history of Occator that help in testing the hypotheses of its formation. We used high-resolution images of the Dawn Framing Camera obtained close to the end of the mission. We found a long-lasting and recent period of cryovolcanic activity, which started ≤9 Myr ago and lasted for several million years. Several resurfacing events, affecting the faculae and some (dark) solidified impact melt units, are shown to have occurred millions of years after crater formation and the dissipation of the impact-generated heat. These findings are indicative of a deep-seated brine source. Extensive volatile-driven emplacement of bright material occurred in the central floor, causing its subsidence due to mass loss at depth. Finally, a thick (extrusive) dome of bright material was raised in the central depression. The derived chronostratigraphy of Occator is consistent with a recently geologically active world, where salts play a major role in preserving liquid in a heat-starved body.

https://www.sciencedirect.com/science/article/abs/pii/S0032063316301611

was never completely molten, but possibly differentiated into a rocky core, an ice-rich mantle, and may contain remnant internal liquid water. Thermal alteration should contribute to producing a (dark) carbonaceous chondritic-like surface (McCord and Sotin, 2005, Castillo-Rogez and McCord, 2010; Castillo-Rogez et al., 2011; Nathues et al., 2015) containing ammoniated phyllosilicates (King et al., 1992; De Sanctis et al., 2015, De Sanctis et al., 2016). Here we show and analyse global contrast-rich colour mosaics, derived from a camera on-board Dawn at Ceres (Russell et al., 2016). Colours are unexpectedly more diverse on global scale than anticipated by Hubble Space Telescope (Li et al., 2006) and ground-based observations (Reddy et al. 2015). Dawn data led to the identification of five major colour units. The youngest units identified by crater counting, termed bright and bluish units, are exclusively found at equatorial and intermediate latitudes. We identified correlations between the distribution of the colour units, crater size, and formation age, inferring a crustal stratigraphy. Surface brightness and spectral properties are not correlated. The youngest surface features are the bright spots at crater Occator (~Ø 92km). Their colour spectra are highly consistent with the presence of carbonates while most of the remaining surface resembles modifications of various types of ordinary carbonaceous chondrites.

https://www.nature.com/articles/s41550-018-0574-1

10k m3 per year ===https://www.lpl.arizona.edu/~shane/publications/platz_etal_nature_astronomy_2016.pdf We identify a minimum of 634 permanently shadowed craters. Bright deposits are detected on the floors of just 10 of these craters in multiscattered light. We spectroscopically identify one of the bright deposits as water ice. This detection strengthens the evidence that permanently shadowed areas have preserved water ice on airless planetary bodies.

https://www.nasa.gov/feature/jpl/where-is-the-ice-on-ceres-new-nasa-dawn-findings

"These studies support the idea that ice separated from rock early in Ceres’ history, forming an ice-rich crustal layer, and that ice has remained near the surface over the history of the solar system," said Carol Raymond, deputy principal investigator of the Dawn mission, based at NASA's Jet Propulsion Laboratory, Pasadena, California.

"On Ceres, ice is not just localized to a few craters. It's everywhere, and nearer to the surface with higher latitudes," said Thomas Prettyman, principal investigator of Dawn's gamma ray and neutron detector (GRaND), based at the Planetary Science Institute, Tucson, Arizona.

https://www.sciencedirect.com/science/article/abs/pii/S0012821X17304405

Ceres has a mechanically strong crust with maximum effective viscosity ∼1025 Pa s. Combined with density constraints, this rheology suggests a crustal composition of carbonates or phyllosilicates, water ice, and at least 30 volume percent (vol.%) low-density, high-strength phases most consistent with salt and/or clathrate hydrates. The inference of these crustal materials supports the past existence of a global ocean, consistent with the observed surface composition. Meanwhile, we infer that the uppermost ≥60 km of the silicate-rich mantle is mechanically weak with viscosity <1021 Pa s, suggesting the presence of liquid pore fluids in this region and a low temperature history that avoided igneous differentiation due to late accretion or efficient heat loss through hydrothermal processes.

https://ui.adsabs.harvard.edu/abs/2016DPS....4840705C/abstract

If Ceres formed as an ice-rich body, as suggested by its low density and the detection of ammoniated phyllosilicates [1], then it should have differentiated an ice-dominated shell, analogous to large icy satellites [2]. Instead, Dawn observations revealed an enrichment of Ceres' shell in strong materials, either a rocky component and/or salts and gas hydrates [3, 4, 5, 6]. We have explored several scenarios for the emplacement of Ceres' surface. Endogenic processes cannot account for its overall homogeneity. Instead we suggest that Ceres differentiated an icy shell upon freezing of its early ocean that was removed as a consequence of frequent exposure by impacting after the dwarf planet migrated from a cold accretional environment to the warmer outer main belt (or when the solar nebula dissipated, if Ceres formed in situ). This scenario implies that Ceres' current surface represents the interface between the original ice shell and the top of the frozen ocean, a region that is extremely rich chemistry-wise, as illustrated by the mineralogical observations returned by Dawn [7]. Thermal modeling shows that the shell could remain warm over the long term and offer a setting for the generation of brines that may be responsible for the emplacement of Ahuna Mons [8] and Occator's bright spots [7] on an otherwise homogeneous surface [9]. An important implication is that Ceres' surface offers an analog for better understanding the deep interior and chemical evolution of large ice-rich bodies

https://advances.sciencemag.org/content/4/3/eaao3757

The orbital parameters of Ceres could justify such a cyclical trend (see Fig. 4B). After the period covered by the observations, Ceres approaches the summer solstice, close to perihelion, where the temperature of the shadowed area increases, possibly triggering also the sublimation of water ice previously accumulated on the cold wall or sublimating pristine water ice with higher rate than its exposure.

https://www.planetary.org/space-images/seasons-on-ceres

the gravitational tugs of Jupiter and Saturn, despite their distance, tip the axis. The angle can change from as little as 2 degrees to as much as 20 degrees in only about 12,000 years, which astronomers consider to be very fast.

https://www.nature.com/articles/ngeo2743

most of Ceres’s largest craters are several kilometres deep, and are therefore inconsistent with the existence of an ice-rich subsurface. We further show from numerical simulations that the absence of viscous relaxation over billion-year timescales implies a subsurface viscosity that is at least one thousand times greater than that of pure water ice. We conclude that Ceres’s shallow subsurface is no more than 30% to 40% ice by volume, with a mixture of rock, salts and/or clathrates accounting for the other 60% to 70%. However, several anomalously shallow craters are consistent with limited viscous relaxation and may indicate spatial variations in subsurface ice content.

https://advances.sciencemag.org/content/4/3/e1701645?intcmp=trendmd-adv

Nevertheless, the detection of Na2CO3, NH4 salts (9), and hydrated sodium carbonates provides major constraints on Ceres’ chemical evolution. NH4 salts are speculated to be unstable over geologic time (27). Hydrated sodium carbonates are not stable on airless surfaces and dehydrate upon exposure to vacuum and irradiation over Myr timescales (25). Destabilization on the surface involves both dehydration and decarbonation; for example, Na2CO3·H2O in Na2CO3 + H2O(g) (9, 25, 27). The detection of hydrated Na carbonates supports an aqueous origin of Na carbonates followed by their partial decomposition (mainly dehydration) in surface environments. This implies that sites rich in hydrated carbonates have been formed/exposed recently (a few million years), and dehydration of hydrated Na carbonates is still ongoing. This is in accordance with crater counting and modeling that predict recent formation, within tens to hundreds of millions of years (28, 35).

The different chemical forms of the sodium carbonate, their fresh appearance, morphological settings, and the uneven distribution on Ceres indicate that the formation, exposure, dehydration, and destruction processes of carbonates are recurrent and continuous in recent geological time, implying a still-evolving body and modern processes involving fluid water.

https://trs.jpl.nasa.gov/bitstream/handle/2014/46193/CL%2316-3736.pdf?sequence=1&isAllowed=y

HAMO and LMO images

https://vtechworks.lib.vt.edu/bitstream/handle/10919/99271/maps.13063.pdf?sequence=1&isAllowed=y

Crater depths (Bland 2013; Bland et al. 2016) and topographic power spectra (Ermakov et al. 2017; Fu et al. 2017) constrain the rheology of the outer 40– 100 km shell of Ceres. This in turn places constraints on the allowable composition of the outer 40–100 km shell. Crater relaxation limits the ice content of the outer 40 km of Ceres to be no more than 35%, with a stronger (more viscous) component or components making up the bulk of the crust (Bland et al. 2016; Fu et al. 2017). Ahuna Mons, the only volcanic construction identified on Ceres’s surface, indicates that brines at depth existed <200 My ago in at least one location (Ruesch et al. 2016), raising the possibility that a briny liquid subsurface layer may still be present, if not globally at least in local regions, as also suggested by Fu et al. (2017). Gravity and topography from the Dawn spacecraft indicate that Ceres is a partially differentiated body (Park et al. 2016). The gravity and topography constraints allow for a range of density structures. For example, assuming a partially differentiated body with a CM chondrite composition, Park et al. inferred a 70–190 km thick outer shell with a density of 1680– 1950 kg m3 and an interior with a density of 2460– 2900 kg m3

Whether Ceres’s differentiation proceeded as far as to produce a partially dehydrated silicate core, or even small iron core, remains an open question. Analysis of Dawn’s GRaND data is consistent with several weight percent iron depletion in the equatorial average concentration of elemental iron relative to cosmochemical iron abundance or an average of CI/CM chondrites (Prettyman et al. 2017). The joint measurements of iron and hydrogen concentrations imply that Ceres underwent some degree of ice-rock fractionation, if the starting composition was similar to carbonaceous chondrites (Prettyman et al. 2017). In this work we address this question of whether Ceres may have a high-density core using the Dawn shape data and hydrostatic flattening constraints. Although Park et al. (2016) and Ermakov et al. (2017) restricted their focus to two-layer models for the radial density structure of Ceres, we consider a suite of threelayer density models varying the densities and radii of the layers (shells). After computing a large ensemble of density models that are consistent with the mass and shape observations, we compare the results with several surface compositions and discuss how these assumed compositions would impact the interior density structure.

The inferred crustal density range of 1200– 1357 kg m3 is consistent with low-density mineral phases including water, carbonates, salts, serpentine, ammonia-bearing hydrated minerals, and organic material (Ammannito et al. 2016; De Sanctis et al. 2016, 2017). The crustal composition of water ice, carbonates, phyllosilicates, and salt and/or clathrate hydrate phases is most consistent with models of an ancient ocean layer that underwent progressive freezing, leading to the concentration of salts (Neveu and Desch 2015; Fu et al. 2017). It is possible that rocky particles enriched in magnetite and sulfides were concentrated at depth, per their greater densities, during the differentiation phase, when Ceres held a deep ocean. A similar model was proposed for icy satellites by Scott et al. (2002). Using data from Dawn’s Gamma Ray and Neutron Detector (GRaND), Prettyman et al. (2017) determined the equatorial average concentration of elemental iron at the surface of Ceres is 16 1 wt%. This is ~10% lower than cosmochemical iron abundances (e.g., McDonough and Sun 1995) and 15–30% lower than CM and CI chondrite averages (Lodders and Fegley 1998), and may provide a possible mechanism and source for the highdensity component in the large core density models.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2018JE005910

Adding up the expected vaporization from the icy spots on Ceres, Landis et al. show that the total water production from those spots is 2 orders of magnitude short of the measured water vapor in the exosphere. However, substantial amounts of water ice may be hidden in intimate mixture with other surface components. For example, Yoldi et al. (2015) mixed water ice with a lunar regolith simulant, and, depending on ice grain size, up to 40–80% of water ice abundance did not significantly increase the reflectance of the regolith. Furthermore, an organic mantle of a few millimeter thickness is sufficient to completely suppress the near‐infrared absorption lines of water ice (Poch et al., 2016). A global surface or near‐surface ice coverage would be inconsistent with the gamma and neutron detector data from Dawn (Prettyman et al., 2017). However, the resolution of the gamma and neutron detector is limited, and the presence of local surface ice created by small impacts is possible

http://www.lalyreduquebec.com/Biblio/CeresDiscovery.pdf

The penultimate of 10 sons, most of whom died as children, his parents worried about his health and for this reason quickly baptized him at home. The register of baptisms of St. Maurizio Church clearly specifies “ob imminens vitae periculum,” or “because of impending danger of death”

Following the tradition that encouraged younger children of wealthy and noble families to take holy orders, Giuseppe joined the Teatine order at the age of 19.

Accademia dei Regi Studi of Palermo (which became the University of Palermo in 1806); a few years later, in 1787, he was named to the Chair of Astronomy even though he was not yet even an amateur astronomer. In a matter of only a few years, however, he was to become one of the most respected astronomers of his time

In March 1787, soon after he was charged with overseeing the construction of a new observatory at Palermo, Piazzi departed for a three-year stay at the major astronomical centers of Paris and London. During his travels he gained the esteem and friendship of some of the most reputed astronomers of the time, including Lalande, Messier, Mechain, Cassini, Maskelyne, and Herschel.

5-foot Palermo Circle (Fig. 2), whose accuracy was regarded to be much superior to that of any other existing instrument (Lalande, 1803), Piazzi centered his scientific program on the accurate measurements of stellar positions. His observational technique required that each star had to be observed for at least four nights before its position could be established

1803 of his first star catalog (Piazzi, 1803). For this highly regarded work, he was awarded the prize for mathematics and physics at the Institut National de France, Fondation Lalande, (Lalande, 1804) and was elected a fellow of the Royal Society. It was while working on this catalog that Piazzi, on January 1, 1801, unexpectedly discovered Ceres, the “missing planet” between the orbits of Mars and Jupiter

Piazzi, having observed the new star for a total of 14 nights, finally decided to write to Bode and to Barnaba Oriani in Milan.

I have announced this star as a comet, but since it shows no nebulosity, and moreover, since it had a slow and rather uniform motion, I surmise that it could be something better than a comet. However, I would not by any means advance publicly this conjecture. As soon as I shall have a larger number of observations, I will try to compute its elements.

I have observed a comet in Taurus... It is very tiny, and reaches at most a star of the 8th magnitude without appreciable nebulosity. Please, let me know if it has already been observed by other astronomers, for in this case I will not bother with the calculation of its orbit.

He [Bode]quickly calculated a circular orbit on the basis of his hypothesis about the distance and period of the supposed planet, verified that Piazzi’s observations were consistent with this idea, and on March 26 gave a preliminary announcement at the Prussian Academy of Sciences. Immediately afterward he alerted von Zach,

He went as far as to announce the discovery of the new planet to the press in Hamburg, Jena, and Berlin and to name it “Juno” (Bode, 1802). Von Zach was in favor of the name “Hera” proposed by Duke Ernst of Saxe-Gotha 15 years before the object’s discovery (von Zach, 1801a), and this name was at first widely accepted, at least in Germany. Oriani, writing to Piazzi on July 25, 1801, said: “I have to forewarn you that the name Ηρα, or ‘Hera,’ that is Juno has been given to it almost universally in all Germany” (C. A., 1874). Piazzi, who called his planet “Ceres Ferdinandea” in honor of the patron goddess of Sicily and of King Ferdinand of Bourbon (Piazzi, 1801), certainly did not agree. Writing to Oriani on August 25, 1801, he made no secret of his sentiment: “If the Germans think they have the right to name somebody else’s discoveries they can call my new star the way they like: as for me I will always keep it the name of Cerere and I will be very obliged if you and your colleagues will do the same” (C. A., 1874).

What is going on with the Ceres Ferdinandea? Nothing has been found as yet either in France or in Germany. Peoples are starting to doubt: Already sceptics are making jokes about it. What is Devil Piazzi doing? La Lande wrote me that he [Piazzi] has changed again his observations and that he has made a new Edition of them! What does that mean? La Lande in his letter adds: This is why I do not believe in the planet.

Great joy! I thought I had caught this coquette Ceres but the joy lasted less than a minute

All uncertainties were swept definitively away when first von Zach on December 31, 1801, an

As a consequence, the discovery of other asteroids was expected and, in addition, their frequently observed variation in luminosity could be readily explained. In fact, as fragments of an exploded planet they were obviously “lacking roundness” and hence “in their rotation they were not always reflecting the same quantity of light” (Oriani, 1802). Olbers’ theory seemed reasonable and was accepted by many astronomers who further reasoned that for a catastrophic explosion (initially at least) the orbits of all the fragments would have intersected in the place of the explosion and on the opposite side of the Sun

https://www.sciencedirect.com/science/article/abs/pii/S0009281921000076

The surface displays cryovolcanic-like and flow structures, exposed phyllosilicates, carbonates, evaporites and water ice. The subsurface shows partial differentiation, decreasing viscosity with depth, and lateral density heterogeneity. Ceres appears to be geologically active today and possesses liquid water/brine pockets or even an extended liquid layer in the interior, confirming an “Ocean World” designation in today’s vernacular.

https://arxiv.org/ftp/arxiv/papers/1506/1506.04805.pdf

Asteroid spectra are traditionally divided into three major complexes and each of the complexes is divided into individual classes (also called “types”). The S-complex, originally named for its expected silicaceous composition (Chapman et al., 1975), is characterized by spectra with moderate silicate absorption features at 1 and 2 microns. The C-complex, historically named in connection with carbonaceous chondrite meteorites, have low albedo surfaces with spectra that have flat or low slopes and are subtly featured to featureless. Subtle features have absorptions of only a few percent, one of the most notable being the 0.7-micron feature indicating the presence of phyllosilicates likely due to aqueous alteration (Vilas & Gaffey 1989). The X-complex is characterized by moderately sloped and subtly-featured or featureless spectra. It has long been known that the X-complex is compositionally degenerate because it comprises the darkest and brightest surfaces of all asteroids, with albedos as low as a few percent to as high as 50 %. The Tholen taxonomy distinguished the X-complex by albedo, breaking it up into the E, M, and P classes that ranged from high to low albedo. Additionally, there are spectral classes that do not

Initial measurements from the 1940s through the 1970s found that the surface brightness and colors of asteroids trend from medium albedo and moderate spectral slopes (S-complex) for bodies in the inner part of the Main Asteroid Belt to lower albedo and neutral spectral slopes (C-complex) toward the outer part of the Main Belt

Because the asteroids were grouped systematically with heliocentric distance, it was concluded that the asteroids formed close to their current locations. In the context of a relatively static Solar System, where the asteroids were assumed to have formed nearly in place, the variation in the compositions of these asteroids was interpreted to represent the original thermal gradient across the Main Belt from the time of planetesimal formation

The Hungaria region (1.8-2.0 AU, i~20 degrees) is dominated by high albedo (>0.3, Tholen & Barucci, 1989) E-type asteroids that have moderate spectral slopes and often display a 0.49-micron absorption feature (Gradie & Tedesco 1982, Bus & Binzel 2002b). These E-types are considered members of the Hungaria asteroid family (Gaffey et al., 1992) with (434) Hungaria being the brightest member. In the Hungaria region, however, there are a variety of compositional types, including S- and C-complex objects (Carvano et al., 2001). In the Inner Main Belt (2.0-2.5 AU), the dominant players are (4) Vesta (V-type) and a number large S-complex asteroids. C-complex are rare in the Inner Belt at large sizes (D>100 km) where they comprise only 6% of the total mass, but they make up a quarter of the mass at medium sizes (20 km<D<100 km), and are almost equal to the Scomplex by mass at the smallest sizes (5 km<D<20 km). At the same time, the fractions of medium-sloped spectral types (M and P) decrease at smaller sizes. Newly discovered in the Inner Main Belt are D-type asteroids defined by their very red spectral slopes, which had only previously been seen at larger distances aside from a few NEOs that have dynamical origins in the Outer Belt and beyond

An interesting effect of viewing the Inner Main Belt by mass (previous analyses have viewed such statistics by number, not by mass) is the relative insignificance of the Vesta family, the products of a large collision with Vesta, in the Inner Belt (Binzel & Xu 1993). Indeed, only a handful of all Vesta family members, called Vestoids, are larger than 5 km, so their mass contribution even among 5-20 km diameter bodies is miniscule (1% of that size range and region, DeMeo & Carry 2014). Vestoids are significant contributors to the Inner Belt in terms of the total number observed (Parker et al., 2008, Masiero et al., 2013), but it is their high albedo, close distance, and spectral distinctiveness that have biased their discovery and classification. In the Middle Main Belt (2.5-2.82 AU), Ceres (C-type in the Bus-DeMeo taxonomy) and Pallas (B-type) are the largest objects and they comprise roughly 31% and 7%, respectively, of the entire Main Belt by mass. The broad taxonomic makeup of the Inner and Middle Belt at the smallest sizes is essentially identical. In the Outer Main Belt (2.82-3.3 AU), the C-complex dominates by mass with Hygeia being the largest and most massive member. Despite the fact that the relative fraction of S-complex asteroids is small in the Outer Main Belt, their total mass is still quite significant given that the mass in the Outer Belt is 2-10 times greater than in the Inner Belt at each size range. A- and V-types, respectively olivine-dominated and basaltic asteroids, are present in small numbers throughout the Main Belt, aside from those associated with Vesta (Lazzaro et al., 2000, Moskovitz et al., 2008, Sanchez et al., 2014). Their discovery in the Middle and Outer Belts was surprising since differentiated bodies or fragments of them were not expected in the context of the classical understanding of asteroid differentiation.

Partly due to models inability to simultaneously match constraints with the terrestrial planets (the mass of Mars) and with the Asteroid Belt (orbital distributions and water delivery), a recently proposed model, the Grand Tack Model, invokes a scattering implantation of nearly the entire Asteroid Belt population from different parent populations (Walsh et al., 2011). This dramatic migration of the giant planets causes widespread depletion and then mixing of remnant populations in the dynamically stable Asteroid Belt. When Jupiter is migrating inwards it completely depletes all objects native to the current Asteroid Belt. During its outward migration it scatters some remnants of this population back into the Asteroid Belt, and then during the outermost stretches of its migration it also scatters in bodies from more primitive reservoirs between and beyond the formation region of the Giant Planets. This mechanism is distinct from others as it implies separate parent populations for some of the major different compositional classes found in the Asteroid Belt, and also because it results in a low-mass Asteroid Belt from very early on in Solar System history. While it provides first-order matches to these three Asteroid Belt constraints (mass depletion, orbital and taxonomic distributions), they were not a prediction of the model – rather they were a necessary constraint for the model to be viable. Going forward, each of these can be investigated more closely and hopefully limit or rule out some of the free parameters in the current Grand Tack scenario (growth and migration parameters of the giant planets).

https://www.scientificamerican.com/article/nasa-s-dawn-mission-spies-ice-volcanoes-on-ceres/

To find out, the team measured how the speed of the spacecraft changed throughout its orbit to build a detailed map of Ceres’s gravitational field, which in turn revealed regions of high and low density in the crust. Then Raymond and her colleagues combined the density map with models of how heat would travel in an ice-rich crust to reconstruct the aftermath of the Occator impact. The scenario they uncovered, Raymond says, “opens up a new way to think about the geology” of icy bodies such as Ceres, which is the largest object in the asteroid belt. The energy of the impact created a “melt chamber” of liquid water near the surface, as well as fractures in the crust. These fractures, Raymond says, connected the melt chamber to a deep reservoir of liquid water that already existed about 35 kilometers underground. Over the course of millions of years, brine rose through the network of fractures as the melt chamber gradually refroze. Upon reaching the surface, the water rapidly boiled away in the near-vacuum conditions, leaving behind the sodium carbonate and other salts.

Subtle gradations in the reflected light and thermal glow from the central dome in Occator Crater revealed the presence of a mineral called hydrohalite—essentially table salt with ice trapped in its crystal structure. The mineral is common in Earth’s sea ice but had never before been detected elsewhere in the solar system. The team calculated that once exposed on the surface of Ceres, the ice in the hydrohalite would disappear in roughly 100 years, leaving behind solid sodium chloride (which would not be detected by Dawn’s instruments). Thus, the presence of hydrohalite indicated that the brine continues to rise to the surface today. “We nailed the fact that there is ongoing geologic activity,” says Raymond, who is a co-author of all seven studies.

https://meetingorganizer.copernicus.org/EPSC2017/EPSC2017-966.pdf

The globally-averaged Fe/O, Fe/Si, and K/Th ratios were found to be consistent with the HED meteorites [e.g. 2], providing further indication that Vesta is the HED parent body. The elemental data are consistent with a differentiated planetesimal that accreted inside the snow line from a volatile poor source. Vesta’s basaltic regolith contains exogenic hydrogen in the form of hydrated minerals delivered by carbonaceous chondrite impactors

Hydrated minerals, including OH and ammoniated phyllosilicates, are widespread on Ceres [e.g. 4] (Fig. 1C). Beneath the optical surface, the regolith is Hrich, with equatorial concentrations similar to that of the the aqueously-altered CI chondrites. Excess hydrogen near the poles is probably in the form of water ice, which is stable near the surface at high latitudes [5] (Fig. 1D). Analyses of Fe indicate that Ceres’ underwent modest ice-rock fractionation, resulting in a partially differentiated interior [5]. The latest elemental analyses and implications for Ceres’ origin and hydrothermal evolution are presented.

https://www.nasa.gov/jpl/dawn/gullies-on-vesta-suggest-past-water-mobilized-flows

The leading theory to explain the source of the curved gullies is that Vesta has small, localized patches of ice in its subsurface. No one knows the origin of this ice, but one possibility is that ice-rich bodies, such as comets, left part of their ice deep in the subsurface following impact. A later impact would form a crater and heat up some of the ice patches, releasing water onto the walls of the crater.

https://www.researchgate.net/publication/328147297_True_polar_wander_of_Ceres_due_to_heterogeneous_crustal_density

Ceres is the largest body in the main asteroid belt. It was recently explored by the Dawn mission to uncover strong similarities with other icy bodies. The morphological features observed on the surface of Ceres indicate a relatively wide range of water ice concentrations, leading us to investigate the magnitude and distribution of crustal density heterogeneities, and to consider whether they could have caused a reorientation of Ceres. Here, we present three independent and corroborating lines of evidence for the true polar wander of Ceres. Thanks to the global gravity inversion approach applied to the shape and gravity data of Ceres, we find crustal density heterogeneities up to approximately ±0.3 g cm⁻³, with a prominent positive density anomaly aligned with the equator, in the region of Ahuna Mons. The topography shows the remnants of an equatorial ridge compatible with the position of the palaeo-equator, and indicates that Ceres reoriented by approximately 36°, with the palaeo-pole following an indirect path to the current pole of Ceres. The tectonic patterns generated by the true polar wander are in close agreement with the location and orientation of the Samhain Catenae and Uhola Catenae crustal fractures. These results highlight the complex interior structure and richness of processes taking place in Ceres-scale icy bodies. © 2018, The Author(s), under exclusive licence to Springer Nature Limited.

https://iopscience.iop.org/article/10.1086/308769/pdf

less or equal 0.05 parsecs out in 3000 years (entering galactic (g) cloud)

93 cubic parsecs 0.32 solar masses

higher ionisation increases gas cooling, so the heat of the cloud (2400 k higher) suggests the supernova hasn't finished echoing

https://arxiv.org/pdf/astro-ph/0205128v2.pdf

Comparing the stellar content of B1 with the initial mass function derived from the analysis of galactic OB associations, we estimate the number of supernova explosions and find that about 20 supernovae must have occurred during the past∼ 10− 20 million years, which is suggested to be the age of the Local Bubble; the age of the star cluster is about∼ 20− 30 million years. For the first time, this provides strong evidence that the Local Bubble must have been created and shaped by multi-supernova explosions and presumably been reheated more than 1 million years ago, consistent with recent findings of an excess of 60Fe in a deep ocean ferromanganese crust.

Luyten

Born in Dutch East Indies in 1899, Saw Halley's Comet in 1910, took up astronomy by 1912

Returned to Netherlands in 1912

Spoke nine languages by the age of 28

He was a student of Hertzsprung at the University of Lieden

1987 IAU colloquium

We should remember that,…of the 6,000 stars [that] the average human eye could see in the entire sky, probably not more than thirty—or one-half of one percent—are less luminous than the Sun; that probably, of the 700-odd stars nearer than ten parsecs, at least 96% are less luminous than the Sun.

He turned his early interest in proper motions into a better calibration of the HR diagram than had been known at the time.

he was the first to provide a realistic census of stars in the solar neighborhood and an HR diagram more truly representative of the fainter stars that dominate the solar neighborhood

Since 1925 he determined over 200,000 proper motions, itself a testimonial to his stamina and dedication. In 1925 Luyten lost the sight of one eye in a tennis accident. Thus, he accomplished all of this with his remaining eye;

He describes their first encounter: Luyten had compared stellar luminosities from Mount Wilson spectral classifications and from parallaxes and had concluded that, if all M giants were assigned the same luminosity, the mean error in luminosity from parallax would be reduced. Upon seeing this work, Russell, according to Luyten, said, “Even if this were true, I could say it, but you can't.” Young Luyten responded, “I thought that in science the only thing that mattered was what was said not who said it.” These and further encounters allegedly turned the influential Russell against him.

Mr. Fixit replied. “His comment: ‘If you removed the drama and hooey, the planet Venus is left.'”

1950s: automated blink comparator. LHS (Luyten Half Second) and NLTT (New Luyten Two-Tenths) catalogues with the same limits, but with 3,583 and 58,700 stars.