Jump to content

Super-Earth: Difference between revisions

From Wikipedia, the free encyclopedia
Browse history interactively
← Previous editNext edit →
Content deleted Content added
VisualWikitext
OAbot (talk | contribs)
Bots
435,726 edits
m Open access bot: doi added to citation with #oabot.
Line 594: Line 594:
If a super-Earth is detectable by both the radial-velocity and the transit methods, then both its mass and its radius can be determined; thus its average bulk density can be calculated. The actual empirical observations are giving similar results as theoretical models, as it's found that planets larger than approximately 1.6 Earth-radius (more massive than approximately 6 Earth-masses) contain significant fractions of volatiles or H/He gas (such planets appear to have a diversity of compositions that is not well-explained by a single mass-radius relation as that found in rocky planets).<ref>Courtney D. Dressing et al. "[https://arxiv.org/abs/1412.8687 The Mass of Kepler-93b and The Composition of Terrestrial Planets]"</ref><ref>Leslie A. Rogers "[https://arxiv.org/abs/1407.4457 Most 1.6 Earth-Radius Planets are not Rocky]"</ref> After measuring 65 super-Earths smaller than 4 Earth-radii, the empirical data points out that Gas Dwarves would be the most usual composition: there is a trend where planets with radii up to 1.5 Earth-radii increase in density with increasing radius, but above 1.5 radii the average planet density rapidly decreases with increasing radius, indicating that these planets have a large fraction of volatiles by volume overlying a rocky core.<ref>Lauren M. Weiss, and Geoffrey W. Marcy. "[https://arxiv.org/abs/1312.0936 The mass-radius relation for 65 exoplanets smaller than 4 Earth radii]"</ref><ref>Geoffrey W. Marcy, Lauren M. Weiss, Erik A. Petigura, Howard Isaacson, Andrew W. Howard and Lars A. Buchhave. "[https://arxiv.org/abs/1404.2960 Occurrence and core-envelope structure of 1-4x Earth-size planets around Sun-like stars]"</ref><ref>Geoffrey W. Marcy et al. "[https://arxiv.org/abs/1401.4195 Masses, Radii, and Orbits of Small Kepler Planets: The Transition from Gaseous to Rocky Planets]"</ref> Another discovery about exoplanets' composition is that about the gap or rarity observed for planets between 1.5 and 2.0 Earth-radii, which is explained by a bimodal formation of planets (rocky Super-Earths below 1.75 and sub-Neptunes with thick gas envelopes being above such radii).<ref name="doi.org"/>
If a super-Earth is detectable by both the radial-velocity and the transit methods, then both its mass and its radius can be determined; thus its average bulk density can be calculated. The actual empirical observations are giving similar results as theoretical models, as it's found that planets larger than approximately 1.6 Earth-radius (more massive than approximately 6 Earth-masses) contain significant fractions of volatiles or H/He gas (such planets appear to have a diversity of compositions that is not well-explained by a single mass-radius relation as that found in rocky planets).<ref>Courtney D. Dressing et al. "[https://arxiv.org/abs/1412.8687 The Mass of Kepler-93b and The Composition of Terrestrial Planets]"</ref><ref>Leslie A. Rogers "[https://arxiv.org/abs/1407.4457 Most 1.6 Earth-Radius Planets are not Rocky]"</ref> After measuring 65 super-Earths smaller than 4 Earth-radii, the empirical data points out that Gas Dwarves would be the most usual composition: there is a trend where planets with radii up to 1.5 Earth-radii increase in density with increasing radius, but above 1.5 radii the average planet density rapidly decreases with increasing radius, indicating that these planets have a large fraction of volatiles by volume overlying a rocky core.<ref>Lauren M. Weiss, and Geoffrey W. Marcy. "[https://arxiv.org/abs/1312.0936 The mass-radius relation for 65 exoplanets smaller than 4 Earth radii]"</ref><ref>Geoffrey W. Marcy, Lauren M. Weiss, Erik A. Petigura, Howard Isaacson, Andrew W. Howard and Lars A. Buchhave. "[https://arxiv.org/abs/1404.2960 Occurrence and core-envelope structure of 1-4x Earth-size planets around Sun-like stars]"</ref><ref>Geoffrey W. Marcy et al. "[https://arxiv.org/abs/1401.4195 Masses, Radii, and Orbits of Small Kepler Planets: The Transition from Gaseous to Rocky Planets]"</ref> Another discovery about exoplanets' composition is that about the gap or rarity observed for planets between 1.5 and 2.0 Earth-radii, which is explained by a bimodal formation of planets (rocky Super-Earths below 1.75 and sub-Neptunes with thick gas envelopes being above such radii).<ref name="doi.org"/>


Additional studies, conducted with lasers at the [[Lawrence Livermore National Laboratory]] and at the [[Laboratory for Laser Energetics|OMEGA]] laboratory at the [[University of Rochester]] show that the magnesium-silicate internal regions of the planet would undergo phase changes under the immense pressures and temperatures of a super-Earth planet, and that the different phases of this liquid magnesium silicate would separate into layers.
Additional studies, conducted with lasers at the [[Lawrence Livermore National Laboratory]] and at the [[Laboratory for Laser Energetics|OMEGA]] laboratory at the [[University of Rochester]] show that the magnesium-silicate internal regions of the planet would undergo phase changes under the immense pressures and temperatures of a super-Earth planet, and that the different phases of this liquid magnesium silicate would separate into layers.{{Citation needed}}


=== Geologic activity ===
=== Geologic activity ===

Revision as of 16:53, 24 May 2021

Illustration of the inferred size of the super-Earth CoRoT-7b (center) in comparison with Earth and Neptune

A super-Earth is an extrasolar planet with a mass higher than Earth's, but substantially below those of the Solar System's ice giants, Uranus and Neptune, which are 14.5 and 17 times Earth's, respectively.[1] The term "super-Earth" refers only to the mass of the planet, and so does not imply anything about the surface conditions or habitability. The alternative term "gas dwarfs" may be more accurate for those at the higher end of the mass scale, although "mini-Neptunes" is a more common term.

Definition

Artist's impression of the super-Earth exoplanet LHS 1140b.[2]

In general, super-Earths are defined by their masses, and the term does not imply temperatures, compositions, orbital properties, habitability, or environments. While sources generally agree on an upper bound of 10 Earth masses[1][3][4] (~69% of the mass of Uranus, which is the Solar System's giant planet with the least mass), the lower bound varies from 1[1] or 1.9[4] to 5,[3] with various other definitions appearing in the popular media.[5][6][7] The term "super-Earth" is also used by astronomers to refer to planets bigger than Earth-like planets (from 0.8 to 1.2 Earth-radius), but smaller than mini-Neptunes (from 2 to 4 Earth-radii).[8][9] This definition was made by the Kepler space telescope personnel.[10] Some authors further suggest that the term Super-Earth might be limited to rocky planets without a significant atmosphere, or planets that have not just atmospheres but also solid surfaces or oceans with a sharp boundary between liquid and atmosphere, which the four giant planets in the Solar System do not have.[11] Planets above 10 Earth masses are termed massive solid planets,[12] mega-Earths,[13][14] or gas giant planets,[15] depending on whether they are mostly rock and ice or mostly gas.

Discoveries

Illustration of the inferred size of the super-Earth Kepler-10b (right) in comparison with Earth

First

Sizes of Kepler Planet Candidates – based on 2,740 candidates orbiting 2,036 stars as of November 4, 2013 (NASA)

The first super-Earths were discovered by Aleksander Wolszczan and Dale Frail around the pulsar PSR B1257+12 in 1992. The two outer planets (Poltergeist and Phobetor) of the system have masses approximately four times Earth—too small to be gas giants.

The first super-Earth around a main-sequence star was discovered by a team under Eugenio Rivera in 2005. It orbits Gliese 876 and received the designation Gliese 876 d (two Jupiter-sized gas giants had previously been discovered in that system). It has an estimated mass of 7.5 Earth masses and a very short orbital period of about 2 days. Due to the proximity of Gliese 876 d to its host star (a red dwarf), it may have a surface temperature of 430–650 kelvins[16] and be too hot to support liquid water.[17]

First in habitable zone

In April 2007, a team headed by Stéphane Udry based in Switzerland announced the discovery of two new super-Earths within the Gliese 581 planetary system,[18] both on the edge of the habitable zone around the star where liquid water may be possible on the surface. With Gliese 581c having a mass of at least 5 Earth masses and a distance from Gliese 581 of 0.073 astronomical units (6.8 million mi, 11 million km), it is on the "warm" edge of the habitable zone around Gliese 581 with an estimated mean temperature (without taking into consideration effects from an atmosphere) of −3 degrees Celsius with an albedo comparable to Venus and 40 degrees Celsius with an albedo comparable to Earth. Subsequent research suggested Gliese 581c had likely suffered a runaway greenhouse effect like Venus.

Mass and radius values for transiting super-Earths in context of other detected exoplanets and selected composition models. The "Fe" line defines planets made purely of iron, and "H2O" for those made of water. Those between the two lines, and closer to the Fe line, are most likely solid rocky planets, while those near or above the water line are more likely gas and/or liquid. Planets in the Solar System are on the chart, labeled with their astronomical symbols.

Others by year

2006

Two further super-Earths were discovered in 2006: OGLE-2005-BLG-390Lb with a mass of 5.5 Earth masses, which was found by gravitational microlensing, and HD 69830 b with a mass of 10 Earth masses.[1]

2008

The smallest super-Earth found as of 2008 was MOA-2007-BLG-192Lb. The planet was announced by astrophysicist David P. Bennett for the international MOA collaboration on June 2, 2008.[19][20] This planet has approximately 3.3 Earth masses and orbits a brown dwarf. It was detected by gravitational microlensing.

In June 2008, European researchers announced the discovery of three super-Earths around the star HD 40307, a star that is only slightly less massive than our Sun. The planets have at least the following minimum masses: 4.2, 6.7, and 9.4 times Earth's. The planets were detected by the radial velocity method by the HARPS (High Accuracy Radial Velocity Planet Searcher) in Chile.[21]

In addition, the same European research team announced a planet 7.5 times the mass of Earth orbiting the star HD 181433. This star also has a Jupiter-like planet that orbits every three years.[22]

2009

Planet COROT-7b, with a mass estimated at 4.8 Earth masses and an orbital period of only 0.853 days, was announced on 3 February 2009. The density estimate obtained for COROT-7b points to a composition including rocky silicate minerals, similar to the four inner planets of the Solar System, a new and significant discovery.[23] COROT-7b, discovered right after HD 7924 b, is the first super-Earth discovered that orbits a main sequence star that is G class or larger.[24]

The discovery of Gliese 581e with a minimum mass of 1.9 Earth masses was announced on 21 April 2009. It was at the time the smallest extrasolar planet discovered around a normal star and the closest in mass to Earth. Being at an orbital distance of just 0.03 AU and orbiting its star in just 3.15 days, it is not in the habitable zone,[25] and may have 100 times more tidal heating than Jupiter's volcanic satellite Io.[26]

A planet found in December 2009, GJ 1214 b, is 2.7 times as large as Earth and orbits a star much smaller and less luminous than our Sun. "This planet probably does have liquid water," said David Charbonneau, a Harvard professor of astronomy and lead author of an article on the discovery.[27] However, interior models of this planet suggest that under most conditions it does not have liquid water.[28]

By November 2009, a total of 30 super-Earths had been discovered, 24 of which were first observed by HARPS.[29]

2010

Discovered on 5 January 2010, a planet HD 156668 b with a minimum mass of 4.15 Earth masses, is the least massive planet detected by the radial velocity method.[30] The only confirmed radial velocity planet smaller than this planet is Gliese 581e at 1.9 Earth masses (see above). On 24 August, astronomers using ESO's HARPS instrument announced the discovery of a planetary system with up to seven planets orbiting a Sun-like star, HD 10180, one of which, although not yet confirmed, has an estimated minimum mass of 1.35 ± 0.23 times that of Earth, which would be the lowest mass of any exoplanet found to date orbiting a main-sequence star.[31] Although unconfirmed, there is 98.6% probability that this planet does exist.[32]

The National Science Foundation announced on 29 September the discovery of a fourth super-Earth (Gliese 581g) orbiting within the Gliese 581 planetary system. The planet has a minimum mass 3.1 times that of Earth and a nearly circular orbit at 0.146 AU with a period of 36.6 days, placing it in the middle of the habitable zone where liquid water could exist and midway between the planets c and d. It was discovered using the radial velocity method by scientists at the University of California at Santa Cruz and the Carnegie Institution of Washington.[33][34][35] However, the existence of Gliese 581 g has been questioned by another team of astronomers, and it is currently listed as unconfirmed at The Extrasolar Planets Encyclopaedia.[36]

2011

On 2 February, the Kepler Space Observatory mission team released a list of 1235 extrasolar planet candidates, including 68 candidates of approximately "Earth-size" (Rp < 1.25 Re) and 288 candidates of "super-Earth-size" (1.25 Re < Rp < 2 Re).[37][38] In addition, 54 planet candidates were detected in the "habitable zone." Six candidates in this zone were less than twice the size of the Earth [namely: KOI 326.01 (Rp=0.85), KOI 701.03 (Rp=1.73), KOI 268.01 (Rp=1.75), KOI 1026.01 (Rp=1.77), KOI 854.01 (Rp=1.91), KOI 70.03 (Rp=1.96) – Table 6][37] A more recent study found that one of these candidates (KOI 326.01) is in fact much larger and hotter than first reported.[39] Based on the latest Kepler findings, astronomer Seth Shostak estimates "within a thousand light-years of Earth" there are "at least 30,000 of these habitable worlds."[40] Also based on the findings, the Kepler Team has estimated "at least 50 billion planets in the Milky Way" of which "at least 500 million" are in the habitable zone.[41]

On 17 August, a potentially habitable super-Earth HD 85512 b was found using the HARPS as well as a three super-Earth system 82 G. Eridani.[42] On HD 85512 b, it would be habitable if it exhibits more than 50% cloud cover.[43][44] Then less than a month later, a flood of 41 new exoplanets including 10 super-Earths were announced.[45]

On 5 December 2011, the Kepler space telescope discovered its first planet within the habitable zone or "Goldilocks region" of its Sun-like star. Kepler-22b is 2.4 times the radius of the earth and occupies an orbit 15% closer to its star than the Earth to the Sun. This is compensated for however, as the star, with a spectral type G5V is slightly dimmer than the Sun (G2V), and thus the surface temperatures would still allow liquid water on its surface.

On 5 December 2011, the Kepler team announced that they had discovered 2,326 planetary candidates, of which 207 are similar in size to Earth, 680 are super-Earth-size, 1,181 are Neptune-size, 203 are Jupiter-size and 55 are larger than Jupiter. Compared to the February 2011 figures, the number of Earth-size and super-Earth-size planets increased by 200% and 140% respectively. Moreover, 48 planet candidates were found in the habitable zones of surveyed stars, marking a decrease from the February figure; this was due to the more stringent criteria in use in the December data.

Artist's impression of 55 Cancri e in front of its parent star.[46]

On 2011, a density of 55 Cancri e was calculated which turned out to be similar to Earth's. At the size of about 2 Earth radii, it was the largest planet until 2014 which was determined to lack a significant hydrogen atmosphere.[47][48]

On 20 December 2011, the Kepler team announced the discovery of the first Earth-size exoplanets, Kepler-20e and Kepler-20f, orbiting a Sun-like star, Kepler-20.

Planet Gliese 667 Cb (GJ 667 Cb) was announced by HARPS on 19 October 2009, together with 29 other planets, while Gliese 667 Cc (GJ 667 Cc) was included in a paper published on 21 November 2011. More detailed data on Gliese 667 Cc were published in early February 2012.

2012

In September 2012, the discovery of two planets orbiting Gliese 163[49] was announced.[50][51] One of the planets, Gliese 163 c, about 6.9 times the mass of Earth and somewhat hotter, was considered to be within the habitable zone.[50][51]

2013

On 7 January 2013, astronomers from the Kepler space observatory announced the discovery of Kepler-69c (formerly KOI-172.02), an Earth-like exoplanet candidate (1.5 times the radius of Earth) orbiting a star similar to our Sun in the habitable zone and possibly a "prime candidate to host alien life".[52]

In April 2013, using observations by NASA's Kepler mission team led by William Borucki, of the agency's Ames Research Center, found five planets orbiting in the habitable zone of a Sun-like star, Kepler-62, 1,200 light years from Earth. These new super-Earths have radii of 1.3, 1.4, 1.6, and 1.9 times that of Earth. Theoretical modelling of two of these super-Earths, Kepler-62e and Kepler-62f, suggests both could be solid, either rocky or rocky with frozen water.[53]

On 25 June 2013, three "super Earth" planets have been found orbiting a nearby star at a distance where life in theory could exist, according to a record-breaking tally announced on Tuesday by the European Southern Observatory. They are part of a cluster of as many as seven planets that circle Gliese 667C, one of three stars located a relatively close 22 light years from Earth in the constellation of Scorpio, it said. The planets orbit Gliese 667C in the so-called Goldilocks Zone — a distance from the star at which the temperature is just right for water to exist in liquid form rather than being stripped away by stellar radiation or locked permanently in ice.[citation needed]

2014

In May 2014, previously discovered Kepler-10c was determined to have the mass comparable to Neptune (17 Earth masses). With the radius of 2.35 R🜨, it is currently the largest known planet likely to have a predominantly rocky composition.[54] At 17 Earth masses it is well above the 10 Earth mass upper limit that is commonly used for the term 'super-Earth' so the term mega-Earth has been proposed.[14] However, in July 2017, more careful analysis of HARPS-N and HIRES data showed that Kepler-10c was much less massive than originally thought, instead around 7.37 (6.18 to 8.69) ME with a mean density of 3.14 g/cm3. Instead of a primarily rocky composition, the more accurately determined mass of Kepler-10c suggests a world made almost entirely of volatiles, mainly water.[55]

2015

On 6 January 2015, NASA announced the 1000th confirmed exoplanet discovered by the Kepler space telescope. Three of the newly confirmed exoplanets were found to orbit within habitable zones of their related stars: two of the three, Kepler-438b and Kepler-442b, are near-Earth-size and likely rocky; the third, Kepler-440b, is a super-Earth.[56]

On 30 July 2015, Astronomy & Astrophysics said they found a planetary system with three super-Earths orbiting a bright, dwarf star. The four-planet system, dubbed HD 219134, had been found 21 light years from Earth in the M-shaped northern hemisphere of constellation Cassiopeia, but it is not in the habitable zone of its star. The planet with the shortest orbit is HD 219134 b, and is Earth's closest known rocky, and transiting, exoplanet.[57][58][59]

2016

In February 2016, it was announced that NASA's Hubble Space Telescope had detected hydrogen and helium (and suggestions of hydrogen cyanide), but no water vapor, in the atmosphere of 55 Cancri e, the first time the atmosphere of a super-Earth exoplanet was analyzed successfully.[60]

In August 2016, astronomers announce the detection of Proxima b, an Earth-sized exoplanet that is in the habitable zone of the red dwarf star Proxima Centauri, the closest star to the Sun.[61] Due to its closeness to Earth, Proxima b may be a flyby destination for a fleet of interstellar StarChip spacecraft currently being developed by the Breakthrough Starshot project.[61]

2018

In February 2018, K2-141b, a rocky ultra-short period planet (USP) Super-Earth, with a period of 0.28 days orbiting the host star K2-141 (EPIC 246393474) was reported.[62] Another Super-Earth, K2-155d, is discovered.[63]

In July 2018, the discovery of 40 Eridani b was announced.[64] At 16 light-years it is the closest super-Earth known, and its star is the second-brightest hosting a super-Earth.[65][64]

2019

In July 2019, the discovery of GJ 357 d was announced. 31 light years from the Solar System, the planet is at least 6.1 ME.

2021

In 2021 the exoplanet G 9-40 b was discovered

Solar System

Main article: Planet Nine

The Solar System contains no known super-Earths, because Earth is the largest terrestrial planet in the Solar System, and all larger planets have both at least 14 times the mass of Earth and thick gaseous atmospheres without well-defined rocky or watery surfaces; that is, they are either gas giants or ice giants, not terrestrial planets. In January 2016, the existence of a hypothetical super-Earth ninth planet in the Solar System, referred to as Planet Nine, was proposed as an explanation for the orbital behavior of six trans-Neptunian objects, but it is speculated to also be an ice giant like Uranus or Neptune.[66][67] However, with its refined model in 2019 constraining it to around 5 Earth masses, it is most likely to be a super-Earth.[68]

Characteristics

Density and bulk composition

Comparison of sizes of planets with different compositions[69]

Due to the larger mass of super-Earths, their physical characteristics may differ from Earth's; theoretical models for super-Earths provide four possible main compositions according to their density: low-density super-Earths are inferred to be composed mainly of hydrogen and helium (mini-Neptunes); super-Earths of intermediate density are inferred to either have water as a major constituent (ocean planets), or have a denser core enshrouded with an extended gaseous envelope (gas dwarf or sub-Neptune). A super-Earth of high density is believed to be rocky and/or metallic, like Earth and the other terrestrial planets of the Solar System. A super-Earth's interior could be undifferentiated, partially differentiated, or completely differentiated into layers of different composition. Researchers at Harvard Astronomy Department have developed user-friendly online tools to characterize the bulk composition of the super-Earths.[70][71] A study on Gliese 876 d by a team around Diana Valencia[1] revealed that it would be possible to infer from a radius measured by the transit method of detecting planets and the mass of the relevant planet what the structural composition is. For Gliese 876 d, calculations range from 9,200 km (1.4 Earth radii) for a rocky planet and very large iron core to 12,500 km (2.0 Earth radii) for a watery and icy planet. Within this range of radii the super-Earth Gliese 876 d would have a surface gravity between 1.9g and 3.3g (19 and 32 m/s2). However, this planet is not known to transit its host star.

The limit between rocky planets and planets with a thick gaseous envelope is calculated with theoretical models. Calculating the effect of the active XUV saturation phase of G-type stars over the loss of the primitive nebula-captured hydrogen envelopes in extrasolar planets, it's obtained that planets with a core mass of more than 1.5 Earth-mass (1.15 Earth-radius max.), most likely cannot get rid of their nebula captured hydrogen envelopes during their whole lifetime.[72] Other calculations point out that the limit between envelope-free rocky super-Earths and sub-Neptunes is around 1.75 Earth-radii, as 2 Earth-radii would be the upper limit to be rocky (a planet with 2 Earth-radii and 5 Earth-masses with a mean Earth-like core composition would imply that 1/200 of its mass would be in a H/He envelope, with an atmospheric pressure near to 2.0 GPa or 20,000 bar).[73] Whether or not the primitive nebula-captured H/He envelope of a super-Earth is entirely lost after formation also depends on the orbital distance. For example, formation and evolution calculations of the Kepler-11 planetary system show that the two innermost planets Kepler-11b and c, whose calculated mass is ≈2 M⊕ and between ≈5 and 6 M⊕ respectively (which are within measurement errors), are extremely vulnerable to envelope loss.[74] In particular, the complete removal of the primordial H/He envelope by energetic stellar photons appears almost inevitable in the case of Kepler-11b, regardless of its formation hypothesis.[74]

If a super-Earth is detectable by both the radial-velocity and the transit methods, then both its mass and its radius can be determined; thus its average bulk density can be calculated. The actual empirical observations are giving similar results as theoretical models, as it's found that planets larger than approximately 1.6 Earth-radius (more massive than approximately 6 Earth-masses) contain significant fractions of volatiles or H/He gas (such planets appear to have a diversity of compositions that is not well-explained by a single mass-radius relation as that found in rocky planets).[75][76] After measuring 65 super-Earths smaller than 4 Earth-radii, the empirical data points out that Gas Dwarves would be the most usual composition: there is a trend where planets with radii up to 1.5 Earth-radii increase in density with increasing radius, but above 1.5 radii the average planet density rapidly decreases with increasing radius, indicating that these planets have a large fraction of volatiles by volume overlying a rocky core.[77][78][79] Another discovery about exoplanets' composition is that about the gap or rarity observed for planets between 1.5 and 2.0 Earth-radii, which is explained by a bimodal formation of planets (rocky Super-Earths below 1.75 and sub-Neptunes with thick gas envelopes being above such radii).[9]

Additional studies, conducted with lasers at the Lawrence Livermore National Laboratory and at the OMEGA laboratory at the University of Rochester show that the magnesium-silicate internal regions of the planet would undergo phase changes under the immense pressures and temperatures of a super-Earth planet, and that the different phases of this liquid magnesium silicate would separate into layers.[citation needed]

Geologic activity

Further theoretical work by Valencia and others suggests that super-Earths would be more geologically active than Earth, with more vigorous plate tectonics due to thinner plates under more stress. In fact, their models suggested that Earth was itself a "borderline" case, just barely large enough to sustain plate tectonics.[80] However, other studies determine that strong convection currents in the mantle acting on strong gravity would make the crust stronger and thus inhibit plate tectonics. The planet's surface would be too strong for the forces of magma to break the crust into plates.[81]

Evolution

New research suggests that the rocky centres of super-Earths are unlikely to evolve into terrestrial rocky planets like the inner planets of the Solar System because they appear to hold on to their large atmospheres. Rather than evolving to a planet composed mainly of rock with a thin atmosphere, the small rocky core remains engulfed by its large hydrogen-rich envelope.[82][83]

Theoretical models show that Hot Jupiters and Hot Neptunes can evolve by hydrodynamic loss of their atmospheres to Mini-Neptunes (as it could be the Super-Earth GJ 1214 b),[84] or even to rocky planets known as chthonian planets (after migrating towards the proximity of their parent star). The amount of the outermost layers that is lost depends on the size and the material of the planet and the distance from the star.[74] In a typical system a gas giant orbiting 0.02 AU around its parent star loses 5–7% of its mass during its lifetime, but orbiting closer than 0.015 AU can mean evaporation of the whole planet except for its core.[85][86]

The low densities inferred from observations imply that a fraction of the super-Earth population has substantial H/He envelopes, which may have been even more massive soon after formation.[87] Therefore, contrary to the terrestrial planets of the solar system, these super-Earths must have formed during the gas-phase of their progenitor protoplanetary disk.[88]

Temperatures

Since the atmospheres, albedo and greenhouse effects of super-Earths are unknown, the surface temperatures are unknown and generally only an equilibrium temperature is given. For example, the black-body temperature of the Earth is 255.3 K (−18 °C or 0 °F ).[89] It is the greenhouse gases that keep the Earth warmer. Venus has a black-body temperature of only 184.2 K (−89 °C or −128 °F ) even though Venus has a true temperature of 737 K (464 °C or 867 °F ).[90] Though the atmosphere of Venus traps more heat than Earth's, NASA lists the black-body temperature of Venus based on the fact that Venus has an extremely high albedo (Bond albedo 0.90, Visual geometric albedo 0.67),[90] giving it a lower black body temperature than the more absorbent (lower albedo) Earth.

Magnetic field

Earth's magnetic field results from its flowing liquid metallic core, but in super-Earths the mass can produce high pressures with large viscosities and high melting temperatures which could prevent the interiors from separating into different layers and so result in undifferentiated coreless mantles. Magnesium oxide, which is rocky on Earth, can be a liquid metal at the pressures and temperatures found in super-Earths and could generate a magnetic field in the mantles of super-Earths.[91] That said, super-Earth magnetic fields are yet to be detected observationally.

Habitability

Further information: Planetary habitability and astrobiology

According to one hypothesis,[92] super-Earths of about two Earth masses may be conducive to life. The higher surface gravity would lead to a thicker atmosphere, increased surface erosion and hence a flatter topography. The end result could be an "archipelago planet" of shallow oceans dotted with island chains ideally suited for biodiversity. A more massive planet of two Earth masses would also retain more heat within its interior from its initial formation much longer, sustaining plate tectonics (which is vital for regulating the carbon cycle and hence the climate) for longer. The thicker atmosphere and stronger magnetic field would also shield life on the surface against harmful cosmic rays.[93]

See also

References

  1. ^ a b c d e Valencia, V.; Sasselov, D. D.; O'Connell, R. J. (2007). "Radius and structure models of the first super-earth planet". The Astrophysical Journal. 656 (1): 545–551. arXiv:astro-ph/0610122. Bibcode:2007ApJ...656..545V. doi:10.1086/509800. S2CID 17656317.
  2. ^ "Newly Discovered Exoplanet May be Best Candidate in Search for Signs of Life - Transiting rocky super-Earth found in habitable zone of quiet red dwarf star". www.eso.org. Retrieved 19 April 2017.
  3. ^ a b Fortney, J. J.; Marley, M. S.; Barnes, J. W. (2007). "Planetary Radii across Five Orders of Magnitude in Mass and Stellar Insolation: Application to Transits". The Astrophysical Journal. 659 (2): 1661–1672. arXiv:astro-ph/0612671. Bibcode:2007ApJ...659.1661F. CiteSeerX 10.1.1.337.1073. doi:10.1086/512120. S2CID 3039909.
  4. ^ a b Charbonneau, D.; et al. (2009). "A super-Earth transiting a nearby low-mass star". Nature. 462 (7275): 891–894. arXiv:0912.3229. Bibcode:2009Natur.462..891C. doi:10.1038/nature08679. PMID 20016595. S2CID 4360404.
  5. ^ Spotts, P. N. (28 April 2007). "Canada's orbiting telescope tracks mystery 'super Earth'". The Hamilton Spectator. Archived from the original on 2015-11-06.
  6. ^ "Life could survive longer on a super-Earth". New Scientist (2629). 11 November 2007.
  7. ^ "A team of ICE/IEEC astronomers announces the discovery of a possible terrestrial-type exoplanet orbiting a star in the constellation of Leo". Institut de Ciències de l'Espai. 10 April 2008. Archived from the original on 1 March 2012. Retrieved 2012-04-28.
  8. ^ Fressin, François; et al. (2013). "The false positive rate of Kepler and the occurrence of planets". Astrophysical Journal. 766 (2): 81. arXiv:1301.0842. Bibcode:2013ApJ...766...81F. doi:10.1088/0004-637X/766/2/81. S2CID 28106368.
  9. ^ a b Fulton, Benjamin J.; et al. (2017). "The California-Kepler Survey. III. A Gap in the Radius Distribution of Small Planets". The Astronomical Journal. 154 (3): 109. arXiv:1703.10375. Bibcode:2017AJ....154..109F. doi:10.3847/1538-3881/aa80eb. S2CID 119339237.{{cite journal}}: CS1 maint: unflagged free DOI (link)
  10. ^ Borucki, William J.; et al. (2011). "Characteristics of planetary candidates observed by Kepler, II: Analysis of the first four months of data". The Astrophysical Journal. 736 (1): 19. arXiv:1102.0541. Bibcode:2011ApJ...736...19B. doi:10.1088/0004-637X/736/1/19. S2CID 15233153.
  11. ^ Seager, S.; Kuchner, M.; Hier-Majumder, C. A.; Militzer, B. (2007). "Mass–radius relationships for solid exoplanets". The Astrophysical Journal. 669 (2): 1279–1297. arXiv:0707.2895. Bibcode:2007ApJ...669.1279S. doi:10.1086/521346. S2CID 8369390.
  12. ^ Seager, S. (2007). "Mass‐Radius Relationships for Solid Exoplanets". The Astrophysical Journal. 669 (2): 1279–1297. arXiv:0707.2895. Bibcode:2007ApJ...669.1279S. doi:10.1086/521346. S2CID 8369390.
  13. ^ Astronomers find a new type of planet: The 'mega-Earth'
  14. ^ a b Dimitar Sasselov (2 June 2014). "Exoplanets: From Exhilarating to Exasperating, 22:59, Kepler-10c: The 'Mega-Earth'". YouTube
  15. ^ Mayor, M.; Pepe, F.; Lovis, C.; Oueloz, D.; Udry, S. (2008). "The quest for very low-mass planets". In Livio, M.; Sahu, K.; Valenti, J. (eds.). A Decade of Extrasolar Planets around Normal Stars. Cambridge University Press. ISBN 978-0521897846.
  16. ^ Rivera, E.; et al. (2005). "A ~7.5 ME Planet Orbiting the Nearby Star, GJ 876". The Astrophysical Journal. 634 (1): 625–640. arXiv:astro-ph/0510508. Bibcode:2005ApJ...634..625R. doi:10.1086/491669. S2CID 14122053.
  17. ^ Zhou, J.-L.; et al. (2005). "Origin and Ubiquity of Short-Period Earth-like Planets: Evidence for the Sequential Accretion Theory of Planet Formation". The Astrophysical Journal. 631 (1): L85–L88. arXiv:astro-ph/0508305. Bibcode:2005ApJ...631L..85Z. doi:10.1086/497094. S2CID 16632198.
  18. ^ Udry, S.; et al. (2007). "The HARPS search for southern extra-solar planets XI. Super-Earths (5 and 8 ME) in a 3-planet system". Astronomy and Astrophysics. 469 (3): L43–L47. arXiv:0704.3841. Bibcode:2007A&A...469L..43U. doi:10.1051/0004-6361:20077612. S2CID 119144195.
  19. ^ Bennett, D. P.; et al. (2008). "Discovery of a Low-mass Planet Orbiting a Low-mass Star in Microlensing Event MOA-2007-BLG-192". Bulletin of the American Astronomical Society. 40: 529. Bibcode:2008AAS...212.1012B.
  20. ^ Bennett, D. P.; et al. (2008). "A Low‐Mass Planet with a Possible Sub‐Stellar‐Mass Host in Microlensing Event MOA‐2007‐BLG‐192". The Astrophysical Journal. 684 (1): 663–683. arXiv:0806.0025. Bibcode:2008ApJ...684..663B. doi:10.1086/589940. S2CID 14467194.
  21. ^ "Trio of 'super-Earths' discovered". BBC News. 16 June 2008. Retrieved 24 May 2010.
  22. ^ "AFP: Astronomers discover clutch of 'super-Earths'". Agence France-Presse. 16 June 2008. Archived from the original on 19 June 2008. Retrieved 28 April 2012.
  23. ^ Queloz, D.; et al. (2009). "The CoRoT-7 planetary system: two orbiting Super-Earths" (PDF). Astronomy and Astrophysics. 506 (1): 303–319. Bibcode:2009A&A...506..303Q. doi:10.1051/0004-6361/200913096.
  24. ^ Howard, A. W.; et al. (2009). "The NASA-UC Eta-Earth Program: I. A Super-Earth Orbiting HD 7924". The Astrophysical Journal. 696 (1): 75–83. arXiv:0901.4394. Bibcode:2009ApJ...696...75H. doi:10.1088/0004-637X/696/1/75. S2CID 1415310.
  25. ^ "Lightest exoplanet yet discovered". European Southern Observatory. 21 April 2009. Retrieved 15 July 2009.
  26. ^ Barnes, R.; Jackson, B.; Greenberg, R.; Raymond, S. N. (2009). "Tidal Limits to Planetary Habitability". The Astrophysical Journal Letters. 700 (1): L30–L33. arXiv:0906.1785. Bibcode:2009ApJ...700L..30B. doi:10.1088/0004-637X/700/1/L30. S2CID 16695095.
  27. ^ Sutter, J. D. (16 December 2009). "Scientists spot nearby 'super-Earth'". CNN. Retrieved 24 May 2010.
  28. ^ Rogers, L.; Seager, S. (2010). "Three Possible Origins for the Gas Layer on GJ 1214b". The Astrophysical Journal. 716 (2): 1208–1216. arXiv:0912.3243. Bibcode:2010ApJ...716.1208R. doi:10.1088/0004-637X/716/2/1208. S2CID 15288792.
  29. ^ "32 planets discovered outside solar system". CNN. 19 October 2009. Retrieved 24 May 2010.
  30. ^ "Second Smallest Exoplanet Found To Date At Keck". W. M. Keck Observatory. 7 January 2010. Retrieved 7 January 2010.
  31. ^ "Richest Planetary System Discovered". European Southern Observatory. 24 August 2010. Retrieved 2010-08-24.
  32. ^ Lovis, C.; et al. (2015). "The HARPS search for southern extra-solar planets XXVII. Up to seven planets orbiting HD 10180: probing the architecture of low-mass planetary systems" (PDF). Astronomy & Astrophysics. 528: A112. arXiv:1411.7048. Bibcode:2011A&A...528A.112L. doi:10.1051/0004-6361/201015577. S2CID 73558341.
  33. ^ Overbye, D. (29 September 2010). "New Planet May Be Able to Nurture Organisms". The New York Times. Retrieved 2 October 2010.
  34. ^ "Newly Discovered Planet May Be First Truly Habitable Exoplanet" (Press release). National Science Foundation. 29 September 2010.
  35. ^ Vogt, S. S.; et al. (2010). "The Lick-Carnegie Exoplanet Survey: A 3.1 ME Planet in the Habitable Zone of the Nearby M3V Star Gliese 581" (PDF). Astrophysical Journal. 723 (1): 954–965. arXiv:1009.5733. Bibcode:2010ApJ...723..954V. doi:10.1088/0004-637X/723/1/954. S2CID 3163906.
  36. ^ "Star: Gl 581". Extrasolar Planets Encyclopaedia. Archived from the original on 4 July 2012. Retrieved 28 April 2012.
  37. ^ a b Borucki, W. J.; et al. (2011). "Characteristics of planetary candidates observed by Kepler, II: Analysis of the first four months of data". The Astrophysical Journal. 736: 19. arXiv:1102.0541. Bibcode:2011ApJ...736...19B. doi:10.1088/0004-637X/736/1/19. S2CID 15233153.
  38. ^ Borucki, W. J.; for the Kepler Team (2010). "Characteristics of Kepler Planetary Candidates Based on the First Data Set: The Majority are Found to be Neptune-Size and Smaller". arXiv:1006.2799. doi:10.1088/0004-637X/728/2/117. S2CID 93116. {{cite journal}}: Cite journal requires |journal= (help)
  39. ^ Grant, A. (8 March 2011). "Exclusive: "Most Earth-Like" Exoplanet Gets Major Demotion—It Isn't Habitable". Discover Magazine – Blogs / 80beats. Kalmbach Publishing. Archived from the original on 9 March 2011. Retrieved 9 March 2011.
  40. ^ Shostak, S. (3 February 2011). "A Bucketful of Worlds". Huffington Post. Retrieved 3 February 2011.
  41. ^ Borenstein, S. (19 February 2011). "Cosmic census finds crowd of planets in our galaxy". Associated Press. Retrieved 2011-02-19.
  42. ^ Pepe, F.; et al. (2011). "The HARPS search for Earth-like planets in the habitable zone: I – Very low-mass planets around HD20794, HD85512 and HD192310". Astronomy & Astrophysics. 534: A58. arXiv:1108.3447. Bibcode:2011A&A...534A..58P. doi:10.1051/0004-6361/201117055. S2CID 15088852.
  43. ^ Kaltenegger, L.; Udry, S.; Pepe, F. (2011). "A Habitable Planet around HD 85512?". arXiv:1108.3561 [astro-ph.EP].
  44. ^ "Star: HD 20781". Extrasolar Planets Encyclopaedia. Retrieved 12 September 2011.
  45. ^ Mayor, M.; et al. (2011). "The HARPS search for southern extra-solar planets XXXIV. Occurrence, mass distribution and orbital properties of super-Earths and Neptune-mass planets". arXiv:1109.2497 [astro-ph].
  46. ^ "First Detection of Super-Earth Atmosphere". Retrieved 18 February 2016.
  47. ^ Winn, J.N.; et al. (2008). "A Super Earth Transiting a Naked-Eye Star". The Astrophysical Journal. 737 (1): L18. arXiv:1104.5230. Bibcode:2011ApJ...737L..18W. doi:10.1088/2041-8205/737/1/L18. S2CID 16768578.
  48. ^ Staff (20 January 2012). "Oozing Super-Earth: Images of Alien Planet 55 Cancri e". Space.com. Retrieved 2012-01-21.
  49. ^ Staff (20 September 2012). "LHS 188 – High proper-motion Star". Centre de données astronomiques de Strasbourg(Strasbourg astronomical Data Center). Retrieved 20 September 2012.
  50. ^ a b Méndez, Abel (29 August 2012). "A Hot Potential Habitable Exoplanet around Gliese 163". University of Puerto Rico at Arecibo (Planetary Habitability Laboratory). Retrieved 20 September 2012.
  51. ^ a b Redd, Nola (20 September 2012). "Newfound Alien Planet a Top Contender to Host Life". Space.com. Retrieved 20 September 2012.
  52. ^ Moskowitz, Clara (January 9, 2013). "Most Earth-Like Alien Planet Possibly Found". Space.com. Retrieved 9 January 2013.
  53. ^ Indian Express
  54. ^ Dumusque, Xavier (2014). "The Kepler-10 Planetary System Revisited by Harps-N: A Hot Rocky World and a Solid Neptune-Mass Planet". The Astrophysical Journal. 789 (2): 154. arXiv:1405.7881. Bibcode:2014ApJ...789..154D. doi:10.1088/0004-637X/789/2/154. S2CID 53475787.
  55. ^ Rajpaul, V.; Buchhave, L. A.; Aigrain, S. (2017), "Pinning down the mass of Kepler-10c: the importance of sampling and model comparison", Monthly Notices of the Royal Astronomical Society: Letters, 471 (1): L125–L130, arXiv:1707.06192, Bibcode:2017MNRAS.471L.125R, doi:10.1093/mnrasl/slx116, S2CID 119243418{{citation}}: CS1 maint: unflagged free DOI (link)
  56. ^ Clavin, Whitney; Chou, Felicia; Johnson, Michele (6 January 2015). "NASA's Kepler Marks 1,000th Exoplanet Discovery, Uncovers More Small Worlds in Habitable Zones". NASA. Retrieved 6 January 2015.
  57. ^ "Astronomers find star with three super-Earths". 30 July 2015. Retrieved 30 July 2015.
  58. ^ "PIA19832: Location of Nearest Rocky Exoplanet Known". NASA. 30 July 2015. Retrieved 30 July 2015.
  59. ^ Chou, Felicia; Clavin, Whitney (30 July 2015). "NASA's Spitzer Confirms Closest Rocky Exoplanet". NASA. Retrieved 31 July 2015.
  60. ^ Staff (16 February 2016). "First detection of super-earth atmosphere". Phys.org. Retrieved 17 February 2016.
  61. ^ a b Chang, Kenneth (24 August 2016). "One Star Over, a Planet That Might Be Another Earth". New York Times. Retrieved 24 August 2016.
  62. ^ Malavolta, Luca; et al. (9 February 2018). "An Ultra-short Period Rocky Super-Earth with a Secondary Eclipse and a Neptune-like Companion around K2-141". The Astronomical Journal. 155 (3): 107. arXiv:1801.03502. Bibcode:2018AJ....155..107M. doi:10.3847/1538-3881/aaa5b5. S2CID 54869937.{{cite journal}}: CS1 maint: unflagged free DOI (link)
  63. ^ Jorgenson, Amber (March 14, 2018). "Potentially habitable super-Earth found during exoplanet search". Astronomy Magazine.
  64. ^ a b Ma, Bo; et al. (2018). "The first super-Earth Detection from the High Cadence and High Radial Velocity Precision Dharma Planet Survey". Monthly Notices of the Royal Astronomical Society. 480 (2): 2411. arXiv:1807.07098. Bibcode:2018MNRAS.480.2411M. doi:10.1093/mnras/sty1933. S2CID 54871108.{{cite journal}}: CS1 maint: unflagged free DOI (link)
  65. ^ Young, Monica (September 17, 2018). "Super-Earth Discovered in (Fictional) Vulcan System". Sky and Telescope. Retrieved Sep 20, 2018.
  66. ^ Batygin, Konstantin; Brown, Michael E. (20 January 2016). "Evidence for a distant giant planet in the Solar System". The Astronomical Journal. 151 (2): 22. arXiv:1601.05438. Bibcode:2016AJ....151...22B. doi:10.3847/0004-6256/151/2/22. S2CID 2701020.{{cite journal}}: CS1 maint: unflagged free DOI (link)
  67. ^ "New planet lurks in Solar System". The Straits Times. The Straits Times. 22 January 2016. Retrieved 8 February 2016.
  68. ^ The Search for Planet Nine findplanetnine.com February 26, 2019
  69. ^ "Scientists Model a Cornucopia of Earth-sized Planets". Goddard Space Flight Center. 24 September 2007. Retrieved 2012-04-28.
  70. ^ www.astrozeng.com
  71. ^ Zeng, Li; Sasselov, Dimitar (2013). "A Detailed Model Grid for Solid Planets from 0.1 through 100 Earth Masses". Publications of the Astronomical Society of the Pacific. 125 (925): 227–239. arXiv:1301.0818. doi:10.1086/669163. JSTOR 10.1086/669163. S2CID 51914911.
  72. ^ H. Lammer et al. "Origin and loss of nebula-captured hydrogen envelopes from `sub´- to `super-Earths´in the habitable zone of Sun-like stars", Monthly Notices of the Royal Astronomical Society, Oxford University Press.
  73. ^ Eric D. Lopez, Jonathan J. Fortney "Understanding the Mass-Radius Relation for Sub-Neptunes: Radius as a Proxy for Composition"
  74. ^ a b c D'Angelo, G.; Bodenheimer, P. (2016). "In Situ and Ex Situ Formation Models of Kepler 11 Planets". The Astrophysical Journal. 828 (1): in press. arXiv:1606.08088. Bibcode:2016ApJ...828...33D. doi:10.3847/0004-637X/828/1/33. S2CID 119203398.{{cite journal}}: CS1 maint: unflagged free DOI (link)
  75. ^ Courtney D. Dressing et al. "The Mass of Kepler-93b and The Composition of Terrestrial Planets"
  76. ^ Leslie A. Rogers "Most 1.6 Earth-Radius Planets are not Rocky"
  77. ^ Lauren M. Weiss, and Geoffrey W. Marcy. "The mass-radius relation for 65 exoplanets smaller than 4 Earth radii"
  78. ^ Geoffrey W. Marcy, Lauren M. Weiss, Erik A. Petigura, Howard Isaacson, Andrew W. Howard and Lars A. Buchhave. "Occurrence and core-envelope structure of 1-4x Earth-size planets around Sun-like stars"
  79. ^ Geoffrey W. Marcy et al. "Masses, Radii, and Orbits of Small Kepler Planets: The Transition from Gaseous to Rocky Planets"
  80. ^ "Earth: A Borderline Planet for Life?" (Press release). Harvard-Smithsonian Center for Astrophysics. 9 January 2008. Retrieved 2012-04-28.
  81. ^ Barry, C. (17 October 2007). "The plate tectonics of alien worlds". Cosmos. Archived from the original on 4 May 2012.
  82. ^ Black, Charles. "Super-Earths are more like mini-Neptunes".
  83. ^ Lammer, Helmut; Erkaev, N. V.; Odert, P.; Kislyakova, K. G.; Leitzinger, M.; Khodachenko, M. L. (2013). "Probing the blow-off criteria of hydrogen-rich 'super-Earths'". Monthly Notices of the Royal Astronomical Society. 430 (2): 1247–1256. arXiv:1210.0793. Bibcode:2013MNRAS.430.1247L. doi:10.1093/mnras/sts705. S2CID 55890198.{{cite journal}}: CS1 maint: unflagged free DOI (link)
  84. ^ Charbonneau, David et al. (2009), A super-Earth transiting a nearby low-mass star, Nature 462, p.891–894
  85. ^ "Exoplanets Exposed to the Core". 2009-04-25. Retrieved 2009-04-25.
  86. ^ Sotin, Christophe; Grasset, O.; Mocquet, A. (2013), Are terrestrial exoplanets Earth-like, Venus-like, or the remnants of gas- or ice-giants?, American Astronomical Society.
  87. ^ D'Angelo, G.; Lissauer, J. J. (2018). "Formation of Giant Planets". In Deeg H., Belmonte J. (ed.). Handbook of Exoplanets. Springer International Publishing AG, part of Springer Nature. pp. 2319–2343. arXiv:1806.05649. Bibcode:2018haex.bookE.140D. doi:10.1007/978-3-319-55333-7_140. ISBN 978-3-319-55332-0. S2CID 116913980.
  88. ^ D'Angelo, G.; Bodenheimer, P. (2013). "Three-dimensional Radiation-hydrodynamics Calculations of the Envelopes of Young Planets Embedded in Protoplanetary Disks". The Astrophysical Journal. 778 (1): 77. arXiv:1310.2211. Bibcode:2013ApJ...778...77D. doi:10.1088/0004-637X/778/1/77. S2CID 118522228.
  89. ^ "Emission Temperature of Planets" (PDF). Caltech Edu. Retrieved 2018-01-13.
  90. ^ a b "Emission Temperature of Planets" (PDF). Caltech Edu. Retrieved 2018-01-13.
  91. ^ Super-Earths Get Magnetic 'Shield' from Liquid Metal, Charles Q. Choi, SPACE.com, November 22, 2012 02:01pm ET,
  92. ^ Better Than Earth, René Heller, Scientific American 312, January, 2015
  93. ^ Box 1 Super-Earths' Big Benefits for Life, René Heller, Scientific American 312, January, 2015

Why is the Earth called a unique planet in our solar system ?

Retrieved from "https://en.wikipedia.org/w/index.php?title=Super-Earth&oldid=1024897145"