(486958) 2014 MU69

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(486958) 2014 MU69
Greyscale image of 2014 MU69[1][a]
Discovery [4][5][6]
Discovered byMarc Buie
Discovery siteHubble Space Telescope
Discovery date26 June 2014
MPC designation(486958) 2014 MU69
  • Ultima Thule (unofficial)[7]
Orbital characteristics[5]
Epoch 2019 April 27 (JD 2458600.5)
Uncertainty parameter 2
Observation arc851 days
Aphelion46.442 AU
Perihelion42.7212447±0.0014309 AU
44.53998 AU
298 yr
0° 0m 11.92s / day
Physical characteristics
Dimensions31.7±0.5 km long axis[10]
"Ultima" 19.46±0.04 km[11]
"Thule" 14.24±0.12 km[11]
Equatorial surface gravity
~ 0.000101971621 g
~ 0.001 m/s2[12]
15±1 h[13]
15.9±0.1 h[10]
North pole right ascension
~ 300°[14]
North pole declination
~ −21°[14]

(486958) 2014 MU69, nicknamed Ultima Thule,[b] is a trans-Neptunian object located in the Kuiper belt. It is a contact binary 31 km (19 mi) long, composed of two planetesimals 19 km (12 mi) and 14 km (9 mi) across, nicknamed "Ultima" and "Thule", respectively, that are joined along their major axes.[14] Ultima, which is flatter than Thule, appears to be an aggregate of 8 or so smaller units,[19] each approximately 6 km (4 mi) across, that fused together before Ultima and Thule came into contact.[12] Because there have been few to no disruptive impacts on 2014 MU69 since it formed, the details of its formation have been preserved.[20] With the New Horizons space probe's flyby at 05:33 on 1 January 2019 (UTC time), 2014 MU69 became the farthest and most primitive object in the Solar System visited by a spacecraft.[21][22]

2014 MU69 was discovered on 26 June 2014 by astronomer Marc Buie[6] using the Hubble Space Telescope as part of a search for a Kuiper belt object for the New Horizons mission to target in its first extended mission; it was chosen over two other candidates to become the primary target of the mission. With an orbital period of 298 years and a low orbital inclination and eccentricity, 2014 MU69 is classified as a cold classical Kuiper belt object.[8] Its nickname, a Greco-Latin term for a place beyond the known world, was chosen as part of a public competition in 2018.[23] The New Horizons team plans to submit a proper name to the International Astronomical Union once the nature of the object is better understood.


When 2014 MU69 was first observed, it was labelled 1110113Y,[24] nicknamed "11" for short.[25][26] Its existence as a potential target of the New Horizons probe was announced by NASA in October 2014[27][28] and it was unofficially designated as "Potential Target 1", or PT1.[26] Its official designation, 2014 MU69 (a provisional designation indicating that it was the 1745th object assigned one for the second half of June 2014), was assigned by the Minor Planet Center (MPC) in March 2015, after sufficient orbital information was gathered.[26] After further observations pinning down its orbit, it was given the permanent minor planet number 486958 on 12 March 2017.[29]

An official name for the object, consistent with the naming guidelines of the International Astronomical Union, will be proposed by the New Horizons team after the spacecraft's flyby, when the properties of (486958) 2014 MU69 are known well enough to choose a suitable name.[30][23] In the interim, NASA invited suggestions from the public on a nickname to be used.[23] The campaign involved 115,000 participants from around the world, who suggested some 34,000 names. Of those, 37 reached the ballot for voting and were evaluated for popularity – this included eight names suggested by the New Horizons team and 29 suggested by the public. "Ultima Thule",[b] which was selected on 13 March 2018,[7] was nominated by about 40 members of the public and obtained the seventh highest number of votes among the nominees.[7] It is named after the Latin phrase ultima Thule (literally "farthest Thule"), an expression referencing the most distant place beyond the borders of the known world.[7] Once it was determined the body was a contact binary, the New Horizons team nicknamed the larger body "Ultima" and the smaller "Thule".[31]

The nickname was criticized due to its use by Nazi occultists as the supposed mythical origin of the Aryan race, aside from its use in ancient Greek and Latin literature. The Thule Society was a key sponsor of what became the Nazi Party, and some modern-day neo-Nazis and members of the alt-right continue to use the term. A few members of the New Horizons team were aware of that association when they selected the nickname, and have since defended their choice. Responding to a question at a press conference, principal investigator Alan Stern said, "Just because some bad guys once liked that term, we’re not going to let them hijack it."[32][33]


(left) Shape model of 2014 MU69 viewed from multiple perspectives. The side view demonstrates the flattened shape of 2014 MU69.[12]
(right) Stereoscopic animation of two LORRI images. (3D version)

2014 MU69 is a contact binary consisting of two lobes attached by a bright, narrow neck.[31] Prior to the New Horizons flyby of 2014 MU69, stellar occultations of 2014 MU69 have provided evidence for its double-lobed shape.[34] The two lobes were likely once two objects that had merged in a slow collision.[35] The larger lobe, nicknamed Ultima, is measured to be 19.5 km (12.1 mi) across while the smaller lobe, Thule, is measured to be 14.2 km (8.8 mi). Overall, the entire object is 31.7 km (19.7 mi) across its longest axis.[10]

The first detailed image of 2014 MU69 confirmed its double-lobed appearance and was described as a "snowman" by New Horizons principal investigator Alan Stern, as the two lobes appeared nearly spherical.[36] On 8 February, one month after the New Horizons flyby, Stern announced that 2014 MU69 was more flattened than initially thought, based on additional images of 2014 MU69 taken by New Horizons after its closest approach. The flattened larger lobe of 2014 MU69 was described as a "pancake", while the smaller lobe was described as a "walnut" as it appeared less flattened compared to the larger lobe.[37] By observing how the unseen sections of 2014 MU69 occulted background stars, scientists were able to then outline the shapes of both lobes.[37] The cause of 2014 MU69's unexpectedly flattened shape is uncertain, though one explanation suggests that the two separate lobes were once rotating rapidly, causing them to become flattened due to centrifugal forces.[38][19]

The longest axes of the two lobes are nearly aligned toward their rotational axis, which is located between the two lobes.[39][40] This alignment of the two lobes suggests that they were mutually locked to each other, likely due to tidal forces, as they merged.[40] This alignment of the two lobes supports the idea that the two had individually formed from the coalescence of a cloud of icy particles.[39]


Surface color[edit]

MVIC color and spectral images of 2014 MU69, showing subtle color variations across its surface. The image on the right is the same MVIC color image superimposed on the higher resolution black and white LORRI image.[c]

The surface color of 2014 MU69 is red.[42] Its color and spectrum was first measured by the Hubble Space Telescope, which revealed its red spectral slope.[43] The color of 2014 MU69 closely matches the reddish colors of other known Kuiper belt objects, and it is notably redder than the dwarf planet Pluto.[40] Due to its strongly red color, 2014 MU69 is considered an 'ultra red' object by the New Horizons team.[42] From color and spectral images of 2014 MU69, the surface displays subtle color variation among its surface features.[42][44] Spectral images of 2014 MU69 show that the neck region and lineation features appear less red while the central region of the smaller lobe appears more red.[12] The larger lobe also displays redder regions, which were nicknamed "thumbprints" by the New Horizons team.[12] The "thumbprints" are located near the larger lobe's limb.[12] Spectral measurements from the New Horizons LEISA instrument has revealed the presence of methanol, water ice, and organic molecules on the surface of 2014 MU69.[42][40]

The red color of 2014 MU69 is caused by the presence of a mix organic compounds (known as tholins) on the surface of 2014 MU69.[45] The tholins are thought to have been produced from ultraviolet solar radiation processing methane and other compounds.[46] The presence of tholins on the surface of 2014 MU69 suggests that other volatile materials such as methane and ammonia are also present on 2014 MU69 as well.[46]


The surface of 2014 MU69 appears lightly cratered.[47][20] The occurrence of impact events on 2014 MU69 is thought to be uncommon, with an very low impact rate over the course of one billion years.[20] The speed of objects impacting 2014 MU69 are thought to be low, with impact speeds of at least 4 km/s (2.5 mi/s).[20] Due to the slow impact speeds, large craters on 2014 MU69 are expected to be rare. With a low frequency of impact events along with the slow speeds of impacts, the surface of 2014 MU69 would remain preserved since its formation. The preserved surface of 2014 MU69 could possibly give hints to its formation process, as well as signs of accreted material.[20][31]

Numerous small pits on the surface of 2014 MU69 were identified in high resolution images from the New Horizons spacecraft.[48][2] The size of these pits are measured to be about 700 m (2,300 ft) across.[48] The exact cause of these pits is unknown; it is debated whether the pits were caused by impacts, the collapse of material, the sublimation of volatile materials, or the venting and escape of volatile gases.[48][2][12]

Surface features[edit]

The geology of 2014 MU69, with comet 67P to scale. Notable surface features are highlighted. (Black lines mark troughs. Elements ma to mh are thought to be the building blocks of Ultima. The lineation circling unit mh has been nicknamed "The Road to Nowhere". lc is the large "Maryland Crater", and sp are smaller pits or craters. The elements labeled bm and dm are bright marks and dark marks, respectively. The bright mark at junction of units mb, mc and mg is one of two nicknamed the "thumbprints".)[12][44]

The surfaces of each lobe of 2014 MU69 display various regions of varying brightness.[49] The reflectivity values vary from 6 percent to 14 percent.[10] Along with brightness variations on the surface of 2014 MU69, various geological features are identified, including troughs and hills.[12] These geological features are thought to have originated from the clumping of smaller objects during the formation of 2014 MU69.[12] The surface gravity on the hilltops of 2014 MU69 is weaker compared to the surface gravity closer between the two lobes, thus material is likely to roll down the hills toward lower elevations, where surface gravity is stronger.[12] This could possibly account for the bright areas on its surface, especially bright lineation features where bright material may be deposited.[42][12][38]

The smaller lobe of 2014 MU69, Thule, bears a large depression feature dubbed "the Maryland Crater" by the New Horizons team.[42][12] The large depression feature is measured to be 8 km (5 mi) across.[42] It is thought to be a possible impact crater formed by an object 700 m (2,300 ft) in size.[47] Bright streaks are notably present in the depression feature, and may be associated with avalanches where bright material rolls down into the depression.[12] The larger lobe of 2014 MU69, Ultima, displays several bright circular patches of terrain including a bright ring-shaped feature informally called "The Road to Nowhere".[2][12][12]

The 'neck' region connecting both lobes of 2014 MU69 is considerably brighter and less red compared to the surfaces of each lobe.[50] The brighter region in the neck is likely composed of a more reflective material different from the surfaces of 2014 MU69's lobes. One hypothesis suggests the bright material in the neck region had likely originated from the deposition of small particles that had fallen from 2014 MU69's lobes over time.[10] Since 2014 MU69's center of gravity lies between the two lobes, small particles are likely to roll down the steep slopes toward the center between each lobe.[50] Another proposal suggests the bright material is produced by the deposition of ammonia ice.[13] Ammonia vapor present on the surface of 2014 MU69 would solidify around the neck region, where gases cannot escape due to the concave shape of the neck.[13]

Internal structure[edit]

The interior of 2014 MU69 is believed to be composed of mostly amorphous water ice and rocky material.[10] Trace amounts of methane and other volatile gases in the form of vapors are also thought to be present in the interior of 2014 MU69, trapped in water ice.[51] The internal structure of 2014 MU69 is expected to have a low porosity, as volatile gases trapped in the interior of 2014 MU69 are thought to escape from the interior.[51] Assuming that 2014 MU69 may have an internal heat source caused by the radioactive decay of radionuclides, the trapped volatile gases inside 2014 MU69 would migrate outward and escape from the surface, similarly to the scenario of outgassing of comets.[51] The escaped gases may subsequently freeze and deposit on the surface of 2014 MU69, and could possibly account for the presence of ices and tholins on its surface.[51][46]

Orbit and rotation[edit]

The orbits of New Horizons potential targets 1 to 3. 2014 MU69 (PT1) is in blue, 2014 OS393 (PT2) is in red and 2014 PN70 is in green.
Near-polar view of 2014 MU69's rotation over a period of seven hours.[3]

2014 MU69's orbital period around the Sun is 298 years. It has a low inclination and low eccentricity compared to other objects in the Kuiper belt.[52] These orbital properties mean that it is a cold classical Kuiper belt object which is unlikely to have undergone significant perturbations.[8] Observations in May and July 2015 as well as in July and October 2016 greatly reduced the uncertainties in the orbit.[15][5]

Results from Hubble Space Telescope observations[53] show that the brightness of 2014 MU69 varies by less than 20 percent as it rotates.[54] This placed significant constraints on the axis ratio of 2014 MU69 to <1.14, having assumed an equatorial view. Prior to the New Horizons flyby of 2014 MU69, the rotation period of 2014 MU69 was unknown as it did not display a rotational light curve amplitude despite 2014 MU69's irregular shape.[55] To explain the lack of its rotational light curve, scientists surmised that 2014 MU69 is rotating on its side, with its rotational axis pointing nearly directly at the approaching New Horizons spacecraft.[55] Subsequent images of 2014 MU69 from New Horizons upon approach confirmed that its rotation is tilted, with its south rotational pole facing towards the Sun.[21][14] Derived from images from New Horizons, the rotational axis of 2014 MU69 is estimated to be tilted an at angle of 92 degrees to its orbit.[14] From the first images of 2014 MU69 by New Horizons, the rotation period of 2014 MU69 was estimated to be roughly 15 to 30 hours.[21] Subsequent images from New Horizons refined its rotation period, giving a value of 15±1 hours.[13]

Mass and density[edit]

The density and mass of 2014 MU69 is unknown. A definite mass and density estimate cannot be given as the two lobes of 2014 MU69 are in contact rather than orbiting each other.[40] Although a possible natural satellite orbiting 2014 MU69 could help determine its mass,[50] no satellites were found orbiting 2014 MU69.[56][40] Derived from the rotation of 2014 MU69, the object is measured to have a very low density, with the minimum estimate of 0.2 g/cm3.[14] Although the estimates may be inaccurate, the densities of each lobe of 2014 MU69 may be measured based on the offset of the object's rotational axis.[14]


Formation sequence of 2014 MU69.[35]

2014 MU69 is thought to have originally been two objects, nicknamed "Ultima" and "Thule", that formed over time from a rotating cloud of small, icy bodies since the formation of the Solar System 4.6 billion years ago.[35][42] Due to streaming instability, icy particles experienced gas drag, slowing down and gravitationally coalescing into clumps of larger particles.[40] Each of the two objects are thought to have accreted separately, and both objects had remained in a mutual orbit around each other after their formation.[42][44] The larger object, Ultima, had likely formed from the coalescence of smaller objects.[44]

Although it is unclear how the two constituents of 2014 MU69 became flattened during its formation, it is thought that the two objects were rotating rapidly, causing their shapes to become flattened due to centrifugal forces.[38] Over time, the rotation rates of the two objects gradually slowed down as they transferred their angular momentum to other orbiting debris left over from their formation.[38] Eventually, loss of momentum, caused by momentum shifting to other bodies in the cloud, caused the pair to slowly spiral closer until they touched – where over time the joints fused together, forming its present double-lobed shape.[35] It is believed that the two objects merged very slowly, at speed of 2 m/s (6.6 ft/s) – comparable to the average walking speed of a person.[44] There is a possible indication of shearing of the surface and terrain caused by the merging of the two objects.[42]

Over a period of at least four billion years since its formation, the frequency of impact events occurring on 2014 MU69 were uncommon due to the slower speeds of objects in the Kuiper Belt.[20] With the lack of frequent cratering events and perturbations of its orbit, the shape and appearance of 2014 MU69 would remain virtually pristine since the conjoining of two separate objects that formed its double-lobed shape.[20][22]



Discovery images of 2014 MU69, cropped from five Wide Field Camera 3 images taken on 26 June 2014.

2014 MU69 was discovered on 26 June 2014 using the Hubble Space Telescope during a preliminary survey to find a suitable Kuiper belt object for the New Horizons probe to fly by. Scientists were searching for an object in the Kuiper belt that the spacecraft could study after Pluto, and their next target had to be reachable on New Horizons' remaining fuel. Using large ground-based telescopes on Earth, researchers began looking in 2011 for candidate objects and searched multiple times per year for several years. But objects that would work for New Horizons were just too distant and faint to be seen through Earth's atmosphere. 2014 MU69 was first spotted by Hubble on 26 June 2014, discovered by astronomer Marc Buie, a member of the New Horizons team.[6]

2014 MU69 is too small and distant to be observed directly from Earth, but scientists have been able to take advantage of a special type of astronomical event called an occultation. This is when the object passes in front of a star from the vantage point of Earth. This event is only visible from certain parts of the Earth, however. The New Horizons team combined data from Hubble and the European Space Agency's Gaia space observatory to figure out exactly when and where on Earth's surface 2014 MU69 would cast a shadow. They determined that occultations would occur on June 3, July 10 and July 17, 2017, and set off for places around the world where they could see 2014 MU69 cover up a different star on each of these dates. Based on this string of three occultations, scientists were able to trace out the object's shape.

In the summer of 2018, nearly fifty New Horizons team members headed to Senegal and Colombia for another occultation event. They obtained information about 2014 MU69 for the spacecraft's flyby.[57][58]

In August 2018, New Horizons recorded its first images of 2014 MU69 for navigation purposes.[59][15][60][61]

2017 occultations[edit]

In June and July 2017, 2014 MU69 occulted three background stars.[62] The team behind New Horizons formed a specialised "KBO Chasers" team to observe these stellar occultations from South America, Africa, and the Pacific Ocean.[63][64][65] On 3 June 2017, two teams of NASA scientists tried to detect the shadow of 2014 MU69 from Argentina and South Africa.[66] When they found that none of their telescopes had observed the object's shadow, it was initially speculated that 2014 MU69 might be neither as large nor as dark as previously expected, and that it might be highly reflective or even a swarm.[67][68] Additional data taken with the Hubble Space Telescope in June and July 2017 revealed that the telescopes had been placed in the wrong location, and that these estimations were incorrect.[69]

2014 MU69 briefly blocked the light from an unnamed star in Sagittarius during an occultation on 17 July 2017. Data from 24 telescopes that captured this event revealed 2014 MU69's possible double-lobed or binary shape. Later, after the flyby in January 2019, the results from the occultation were shown to precisely fit the observed size and shape of the object.[31]

On 10 July 2017, the airborne telescope SOFIA was successfully placed close to the predicted centerline for the second occultation while flying over the Pacific Ocean from Christchurch, New Zealand. The main purpose of those observations was the search for hazardous material like rings or dust near 2014 MU69 that could threaten the New Horizons spacecraft during its flyby in 2019. Data collection was successful. A preliminary analysis suggested that the central shadow was missed;[70] only in January 2018 was it realized that SOFIA had indeed observed a very brief dip from the central shadow.[71] The data collected by SOFIA will also be valuable to put constraints on dust near 2014 MU69.[72][73] Detailed results of the search for hazardous material were presented on the 49th Meeting of the AAS Division for Planetary Sciences, on 20 October 2017.[74]

Artist's concept of 2014 MU69 as a contact binary.[75]

On 17 July 2017, the Hubble Space Telescope was used to check for debris around 2014 MU69, setting constraints on rings and debris within the Hill sphere of 2014 MU69 at distances of up to 75,000 km (47,000 mi) from the main body.[76] For the third and final occultation, team members set up another ground-based "fence line" of 24 mobile telescopes along the predicted ground track of the occultation shadow in southern Argentina (Chubut and Santa Cruz provinces) to better constrain the size of 2014 MU69.[64][77] The average spacing between these telescopes was 4.5 km (2.8 mi).[78] Using the latest observations from Hubble, the position of 2014 MU69 was known with much better precision than for the June 3 occultation, and this time the shadow of 2014 MU69 was successfully observed by at least five of the mobile telescopes.[77] Combined with the SOFIA observations, this will put good constraints on possible debris near 2014 MU69.[73]

Results from the occultation on 17 July showed that 2014 MU69 could have had a very oblong, irregular shape or be a close or contact binary.[34][79] According to the duration of the observed chords, 2014 MU69 was shown to have two "lobes", with diameters of approximately 20 km (12 mi) and 18 km (11 mi), respectively.[54] A preliminary analysis of all collected data suggested that 2014 MU69 was accompanied by an orbiting moonlet about 200–300 km (124–186 mi) away from the primary.[80] It was later realized, however, that an error with the data processing software resulted in a shift in the apparent location of the target. After accounting for the bug, the short dip observed on 10 July is now considered to be a detection of the primary body.[71]

By combining data about its light curve,[81] spectra (e.g. colour), and stellar occultation data,[82] illustrations could rely on known data to create a concept of what it might look like prior to spacecraft flyby.

2018 occultations[edit]

Path of 2014 MU69's shadow on Earth during its 4 August 2018 occultation of an unnamed star in Sagittarius. This event was successfully observed from locations in Senegal and Colombia.

There were two potentially useful 2014 MU69 occultations predicted for 2018: one on 16 July and one on 4 August. Neither of these were as good as the three 2017 events.[62] No attempts were made to observe the 16 July 2018 occultation, which took place over the South Atlantic and the Indian Ocean. For the 4 August 2018 event, two teams, consisting of about 50 researchers in total, went to locations in Senegal and Colombia.[57] The event gathered media attention in Senegal, where it was used as an opportunity for science outreach.[83] Despite some stations being affected by bad weather, the event was successfully observed, as reported by the New Horizons team.[84] Initially, it was unclear whether a chord on the target had been recorded. On 6 September 2018, NASA confirmed that the star had indeed been seen to dip by at least one observer, providing important information about the size and shape of 2014 MU69.[85]

Hubble observations were carried out on 4 August 2018, to support the occultation campaign.[86][57] Hubble could not be placed in the narrow path of the occultation, but due to the favourable location of Hubble at the time of the event, the space telescope was able to probe the region down to 1,600 km (990 mi) from 2014 MU69. This is much closer than the 20,000 km (12,000 mi) region that could be observed during the 17 July 2017 occultation. No brightness changes of the target star have been seen by Hubble, ruling out any optically thick rings or debris down to 1,600 km (990 mi) from 2014 MU69.[85] Results of the 2017 and 2018 occultation campaigns were presented at the 50th meeting of the AAS Division for Planetary Sciences, on 26 October 2018.[87]


Heliocentric positions of the five interstellar probes (squares) and other bodies (circles) until 2020, with launch and flyby dates. Markers denote positions on 1 January of each year, with every fifth year labelled.
Plot 1 is viewed from the north ecliptic pole, to scale; plots 2 to 4 are third-angle projections at 20% scale.
In the SVG file, hover over a trajectory or orbit to highlight it and its associated launches and flybys.
2014 MU69 among the stars of Sagittarius – with and without background star omission (apparent magnitude 20 to 15; New Horizons; late 2018).[88]
View of 2014 MU69 by New Horizons after closest approach. The silhouette of 2014 MU69's shape can be seen among the background stars.

Having completed its flyby of Pluto in July 2015, the New Horizons spacecraft made four course changes in October and November 2015 to place itself on a trajectory towards 2014 MU69.[89] It is the first object to be targeted for a flyby that was discovered after the visiting spacecraft was launched,[15] and is the farthest object in the Solar System ever to be visited by a spacecraft.[26][90][91] New Horizons came within 3,500 km (2,200 mi) of 2014 MU69, three times closer than the spacecraft's earlier encounter with Pluto. Closest approach occurred on January 1, 2019, at 05:33 UTC (Spacecraft Event Time – SCET)[80][92] at which point it was 43.4 AU from the Sun in the direction of the constellation Sagittarius.[93][94][95][96] At this distance, the one-way transit time for radio signals between Earth and New Horizons was 6 hours.[80]

The science objectives of the flyby include characterizing the geology and morphology of 2014 MU69, mapping the surface composition (searching for ammonia, carbon monoxide, methane, and water ice). Surveys of the surrounding environment to detect possible orbiting moonlets, a coma, or rings, were conducted.[80] Images with resolutions showing details of 30 m (98 ft) to 70 m (230 ft) are expected.[80][97] From observations, distant satellites of 2014 MU69 have been excluded to a depth of >29th magnitude.[98] The object has no detectable atmosphere, and no large rings or satellites larger than 1.6 km (1 mi) in diameter.[56] Nonetheless, a search for a related moon (or moons) continues, which may help better explain the formation of 2014 MU69 from two free-flying objects, informally known as "Ultima" and "Thule".[35]

New Horizons made its first detection of 2014 MU69 on 16 August 2018, from a distance of 172 million km (107 million mi).[99] At that time, 2014 MU69 was visible at magnitude 20, in the direction of the constellation Sagittarius.[100] 2014 MU69 was expected to be magnitude 18 by mid-November, and magnitude 15 by mid-December. It reached naked eye brightness (magnitude 6) from the spacecraft's point of view just 3–4 hours before closest approach.[88] If obstacles were detected, the spacecraft had the option of diverting to a more distant rendezvous, though no moons, rings or other hazards were seen.[80][101] High-resolution images from New Horizons were taken on January 1. The first images with medium resolution arrived on the next day.[102] The downlink of data collected from the flyby is expected to last 20 months, through to September 2020.[92]

The download of data was paused from 4 to 10 January 2019 as the spacecraft entered solar conjunction.[103][104]


Observations of 2014 MU69 during closest approach
As shown in this computer simulation provided by NASA's Eyes on the Solar System application, between the morning of 31 December 2018 and 1 January 2019, the New Horizons spacecraft made 33 different observations of 2014 MU69 with the LORRI imaging camera. During the first week after the flyby, only three of these were sent back to Earth.[105]
Animated simulation of 2014 MU69, modelled as two ellipsoids, compared to 12 photos taken during the flyby
Reflectivity variations on 2014 MU69. The area near the neck is the most reflective.[106]

See also[edit]


  1. ^ Greyscale composite of nine 0.025 second exposures taken by the Long Range Reconnaissance Imager (LORRI) aboard New Horizons on 1 January 2019, from a distance of 6,628 kilometres (4,118 mi) at a resolution of 33 metres (108 ft) per pixel.[2] The contact binary object is made up of two lobes named "Ultima" (right) and "Thule" (left). Its axis of rotation is located near the bright "neck" of the object and spins clockwise from this viewpoint.[3]
  2. ^ a b Normally pronounced /ˈθjl/ THEW-lee [US /ˈθl/ THOO-lee].[16] The New Horizons team use this classical pronunciation, the pseudo-Latin pronunciation /ˈtl/ TOO-lay, and the hybrid pronunciation /ˈtl/ TOO-lee.[17][18]
  3. ^ Composite of black and while and color photographs taken respectively by the LORRI and MVIC instruments aboard New Horizons on 1 January 2019.[41]


  1. ^ Chang, Kenneth (22 February 2019). "New Ultima Thule Photos Were Made in a Flash - The images were recorded while the New Horizons spacecraft was moving at more than 32,000 miles per hour". The New York Times. Retrieved 23 February 2019.
  2. ^ a b c d Johns Hopkins University Applied Physics Laboratory (22 February 2019). "Spot On! New Horizons Spacecraft Returns Its Sharpest Views of Ultima Thule". pluto.jhuapl.edu. Archived from the original on 23 February 2019. Retrieved 23 February 2019. ...a resolution of about 110 feet (33 meters) per pixel. [...] This processed, composite picture combines nine individual images taken with the Long Range Reconnaissance Imager (LORRI), each with an exposure time of 0.025 seconds...
  3. ^ a b Johns Hopkins University Applied Physics Laboratory (15 January 2019). "New Movie Shows Ultima Thule from an Approaching New Horizons". New Horizons. Archived from the original on 16 January 2019. Retrieved 16 January 2019. This movie shows the propeller-like rotation of Ultima Thule in the seven hours between 20:00 UT (3 p.m. ET) on Dec. 31, 2018, and 05:01 UT (12:01 a.m.) on Jan. 1, 2019...
  4. ^ a b "JPL Small-Body Database Browser: 486958 (2014 MU69)" (2014-10-22 last obs.). Jet Propulsion Laboratory. Retrieved 15 March 2017.
  5. ^ a b c d e "486958 (2014 MU69)". Minor Planet Center. Retrieved 15 March 2017.
  6. ^ a b c Lauer, Tod; Throop, Henry (January 17, 2019). "The Moment We First Saw Ultima Thule Up Close". Scientific American. Springer Nature. Retrieved January 26, 2019.
  7. ^ a b c d "New Horizons Chooses Nickname for 'Ultimate' Flyby Target". NASA. 13 March 2018. Retrieved 13 March 2018.
  8. ^ a b c Lakdawalla, Emily (15 October 2014). "Finally! New Horizons has a second target". Planetary Society blog. Planetary Society. Archived from the original on 15 October 2014.
  9. ^ Buie, Marc W. "Orbit Fit and Astrometric record for 486958". SwRI (Space Science Department). Retrieved 2018-02-18.
  10. ^ a b c d e f Stern, S.A.; et al. (9 January 2019). "Overview of initial results from the reconnaissance flyby of a Kuiper Belt planetesimal: 2014 MU69". arXiv:1901.02578.
  11. ^ a b Moore, J. M.; McKinnon, W. B.; Spencer, J. R.; Stern, S. A.; et al. (2019). "THE GEOLOGY OF 2014 MU69 ("ULTIMA THULE"): INITIAL RESULTS FROM THE NEW HORIZONS ENCOUNTER" (PDF). Retrieved 21 March 2019.
  12. ^ a b c d e f g h i j k l m n o p "Press Briefing: The developing picture of Ultima Thule". YouTube. Lunar and Planetary Institute. 21 March 2019.
  13. ^ a b c d Katz, J.I. (4 February 2019). "Ultima Thule (486958; 2014 MU69): Necklace, Composition, Rotation, Formation". arXiv:1902.00997.
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