Super-Earth
History and discoveries
History and discoveries
-----------------------

[right\|thumb\|Illustration of the inferred size of the super\-Earth [Kepler\-10b](/wiki/Kepler-10b "Kepler-10b") (right) in comparison with Earth](/wiki/File:Exoplanet_Comparison_Kepler-10_b.png "Exoplanet Comparison Kepler-10 b.png")

### First

[thumb\|upright\=1\.5\|right\|Sizes of [Kepler Planet Candidates](/wiki/Kepler_space_telescope "Kepler space telescope") – based on 2,740 candidates orbiting 2,036 stars as of November 4, 2013 ([NASA](/wiki/NASA "NASA"))](/wiki/File:Size_of_Kepler_Planet_Candidates.jpg "Size of Kepler Planet Candidates.jpg")
The first super\-Earths were discovered by Aleksander Wolszczan and [Dale Frail](/wiki/Dale_Frail "Dale Frail") around the [pulsar](/wiki/Pulsar "Pulsar") [PSR B1257\+12](/wiki/PSR_B1257%2B12 "PSR B1257+12") in 1992\. The two outer planets ([Poltergeist](/wiki/PSR_B1257%2B12_B "PSR B1257+12 B") and [Phobetor](/wiki/PSR_B1257%2B12_C "PSR B1257+12 C")) of the system have masses approximately four times Earth—too small to be gas giants.

The first super\-Earth around a [main\-sequence](/wiki/Main_sequence "Main sequence") star was discovered by a team under [Eugenio Rivera](/wiki/Eugenio_Rivera "Eugenio Rivera") in 2005\. It orbits [Gliese 876](/wiki/Gliese_876 "Gliese 876") and received the designation [Gliese 876 d](/wiki/Gliese_876_d "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](/wiki/Red_dwarf_star "Red dwarf star")), it may have a surface temperature of 430–650 [kelvin](/wiki/Kelvin "Kelvin")
 and be too hot to support liquid water.

### First in habitable zone

In April 2007, a team headed by [Stéphane Udry](/wiki/St%C3%A9phane_Udry "Stéphane Udry") based in Switzerland announced the discovery of two new super\-Earths within the [Gliese 581 planetary system](/wiki/Gliese_581_planetary_system "Gliese 581 planetary system"), both on the edge of the [habitable zone](/wiki/Habitable_zone "Habitable zone") around the star where liquid water may be possible on the surface. With [Gliese 581c](/wiki/Gliese_581c "Gliese 581c") having a mass of at least 5 Earth masses and a distance from [Gliese 581](/wiki/Gliese_581 "Gliese 581") of 0\.073 [astronomical units](/wiki/Astronomical_unit "Astronomical unit") (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 considering effects from an atmosphere) of −3 degrees Celsius with an [albedo](/wiki/Albedo "Albedo") comparable to [Venus](/wiki/Venus "Venus") and 40 degrees Celsius with an albedo comparable to Earth. Subsequent research suggested Gliese 581c had likely suffered a [runaway greenhouse effect](/wiki/Runaway_greenhouse_effect "Runaway greenhouse effect") like Venus.

[thumb\|upright\=1\.5\|right\|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](/wiki/Astronomical_symbols "Astronomical symbols").](/wiki/File:Exoplanet_Mass-Radius_Scatter_Super-Earth.png "Exoplanet Mass-Radius Scatter Super-Earth.png")

### Others by year

#### 2006

Two further possible super\-Earths were discovered in 2006: [OGLE\-2005\-BLG\-390Lb](/wiki/OGLE-2005-BLG-390Lb "OGLE-2005-BLG-390Lb") with a mass of 5\.5 Earth masses, which was found by [gravitational microlensing](/wiki/Gravitational_microlensing "Gravitational microlensing"), and [HD 69830 b](/wiki/HD_69830_b "HD 69830 b") with a mass of 10 Earth masses.

#### 2008

The smallest super\-Earth found as of 2008 was [MOA\-2007\-BLG\-192Lb](/wiki/MOA-2007-BLG-192Lb "MOA-2007-BLG-192Lb"). The planet was announced by astrophysicist David P. Bennett for the international [MOA](/wiki/Microlensing_Observations_in_Astrophysics "Microlensing Observations in Astrophysics") collaboration on June 2, 2008\.

 This planet has approximately 3\.3 Earth masses and orbits a [brown dwarf](/wiki/Brown_dwarf "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](/wiki/HD_40307 "HD 40307"), a star that is only slightly less massive than the [Sun](/wiki/Sun "Sun"). 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](/wiki/Radial_velocity "Radial velocity") method by the [HARPS](/wiki/HARPS "HARPS") (High Accuracy Radial Velocity Planet Searcher) in [Chile](/wiki/Chile "Chile").

In addition, the same European research team announced a planet 7\.5 times the mass of Earth orbiting the star [HD 181433](/wiki/HD_181433 "HD 181433"). This star also has a Jupiter\-like planet that orbits it every three years.

#### 2009

Planet [COROT\-7b](/wiki/COROT-7b "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 that of the Solar System's four inner planets, a new and significant discovery. COROT\-7b, discovered right after [HD 7924 b](/wiki/HD_7924_b "HD 7924 b"), is the first super\-Earth discovered that orbits a [main sequence](/wiki/Main_sequence "Main sequence") star that is [G class](/wiki/G-type_main_sequence_star "G-type main sequence star") or larger.

The discovery of [Gliese 581e](/wiki/Gliese_581e "Gliese 581e") with a [minimum mass](/wiki/Minimum_mass "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, and may have 100 times more tidal heating than Jupiter's volcanic satellite [Io](/wiki/Io_%28moon%29 "Io (moon)").

A planet found in December 2009, [GJ 1214 b](/wiki/GJ_1214%C2%A0b "GJ 1214 b"), is 2\.7 times as large as Earth and orbits a star much smaller and less luminous than the 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. However, interior models of this planet suggest that under most conditions it does not have liquid water.

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

#### 2010

Discovered on 5 January 2010, a planet [HD 156668 b](/wiki/HD_156668%C2%A0b "HD 156668 b") with a [minimum mass](/wiki/Minimum_mass "Minimum mass") of 4\.15 [Earth masses](/wiki/Earth_mass "Earth mass"), is the least massive planet detected by the [radial velocity method](/wiki/Radial_velocity_method "Radial velocity method"). 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](/wiki/HD_10180 "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.
 Although unconfirmed, there is a 98\.6% probability that this planet does exist.

The [National Science Foundation](/wiki/National_Science_Foundation "National Science Foundation") announced on 29 September the discovery of a fourth super\-Earth ([Gliese 581g](/wiki/Gliese_581g "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.

 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](/wiki/The_Extrasolar_Planets_Encyclopaedia "The Extrasolar Planets Encyclopaedia").

#### 2011

On 2 February, the [Kepler Space Observatory mission team](/wiki/Kepler_space_telescope "Kepler space telescope") released a [list of 1235 extrasolar planet candidates](/wiki/Kepler_object_of_interest "Kepler object of interest"), including 68 candidates of approximately "Earth\-size" (Rp \< 1\.25 Re) and 288 candidates of "super\-Earth\-size" (1\.25 Re \< Rp \< 2 Re).
 In addition, 54 planet candidates were detected in the "[habitable zone](/wiki/Habitable_zone "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] A more recent study found that one of these candidates (KOI 326\.01\) is in fact much larger and hotter than first reported.
 Based on the latest Kepler findings, astronomer [Seth Shostak](/wiki/Seth_Shostak "Seth Shostak") estimates "within a thousand light\-years of Earth" there are "at least 30,000 of these habitable worlds."
 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.

On 17 August, a potentially habitable super\-Earth [HD 85512 b](/wiki/HD_85512_b "HD 85512 b") was found using the HARPS as well as a three super\-Earth system [82 G. Eridani](/wiki/82_G._Eridani "82 G. Eridani").
 On HD 85512 b, it would be habitable if it exhibits more than 50% cloud cover.

 Then less than a month later, a flood of 41 new exoplanets, including 10 super\-Earths, were announced.

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](/wiki/Kepler-22b "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](/wiki/G-type_main-sequence_star "G-type main-sequence star"), is slightly dimmer than the Sun (G2V). Thus, 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.

[thumb\|Artist's impression of [55 Cancri e](/wiki/55_Cancri_e "55 Cancri e") in front of its parent star](/wiki/File:Artist%E2%80%99s_impression_of_55_Cancri_e.jpg "Artist’s impression of 55 Cancri e.jpg")

In 2011, a density of [55 Cancri e](/wiki/55_Cancri_e "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.

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](/wiki/Kepler-20 "Kepler-20").

Planet [Gliese 667 Cb](/wiki/Gliese_667_Cb "Gliese 667 Cb") (GJ 667 Cb) was announced by HARPS on 19 October 2009, together with 29 other planets, while [Gliese 667 Cc](/wiki/Gliese_667_Cc "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](/wiki/Gliese_163 "Gliese 163") was announced. One of the planets, [Gliese 163 c](/wiki/Gliese_163_c "Gliese 163 c"), about 6\.9 times the mass of Earth and somewhat hotter, was considered to be within the [habitable zone](/wiki/Habitable_zone "Habitable zone").

#### 2013

On 7 January 2013, astronomers from the [Kepler space observatory](/wiki/Kepler_space_observatory "Kepler space observatory") announced the discovery of [Kepler\-69c](/wiki/Kepler-69c "Kepler-69c") (formerly *KOI\-172\.02*), an [Earth](/wiki/Earth "Earth")\-like [exoplanet](/wiki/Exoplanet "Exoplanet") candidate (1\.5 times the radius of Earth) orbiting a [star](/wiki/Star "Star") similar to the [Sun](/wiki/Sun "Sun") in the [habitable zone](/wiki/Habitable_zone "Habitable zone") and possibly a "prime candidate to host [alien life](/wiki/Extraterrestrial_life "Extraterrestrial life")".

In April 2013, using observations by NASA's Kepler mission team led by [William Borucki](/wiki/William_Borucki "William Borucki"), of the agency's Ames Research Center, found five planets orbiting in the habitable zone of a Sun\-like star, [Kepler\-62](/wiki/Kepler-62 "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](/wiki/Kepler-62e "Kepler-62e") and [Kepler\-62f](/wiki/Kepler-62f "Kepler-62f"), suggests both could be solid, either rocky or rocky with frozen water.

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](/wiki/Gliese_667C "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.

#### 2014

In May 2014, previously discovered [Kepler\-10c](/wiki/Kepler-10c "Kepler-10c") was determined to have the mass comparable to Neptune (17 Earth masses). With the radius of 2\.35 , it is currently the largest known planet likely to have a predominantly rocky composition. 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](/wiki/Mega-Earth "Mega-Earth") has been proposed. [YouTube](https://www.youtube.com/watch?v=t6x29ntnQb0) 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\)  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.

#### 2015

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

On 30 July 2015, *[Astronomy \& Astrophysics](/wiki/Astronomy_and_Astrophysics "Astronomy and Astrophysics")* said they found a planetary system with three super\-Earths orbiting a bright, dwarf star. The four\-planet system, dubbed [HD 219134](/wiki/HR_8832 "HR 8832"), had been found 21 light years from Earth in the M\-shaped northern hemisphere of [constellation Cassiopeia](/wiki/Cassiopeia_%28constellation%29 "Cassiopeia (constellation)"), but it is not in the [habitable zone](/wiki/Circumstellar_habitable_zone "Circumstellar habitable zone") of its star. The planet with the shortest orbit is [HD 219134 b](/wiki/HD_219134_b "HD 219134 b"), and is Earth's closest known rocky, and transiting, exoplanet.

#### 2016

In February 2016, it was announced that [NASA](/wiki/NASA "NASA") [Hubble Space Telescope](/wiki/Hubble_Space_Telescope "Hubble Space Telescope") had detected [hydrogen](/wiki/Hydrogen "Hydrogen") and [helium](/wiki/Helium "Helium") (and suggestions of [hydrogen cyanide](/wiki/Hydrogen_cyanide "Hydrogen cyanide")), but no [water vapor](/wiki/Water_vapor "Water vapor"), in the [atmosphere](/wiki/Atmosphere "Atmosphere") of [55 Cancri e](/wiki/55_Cancri_e "55 Cancri e"), the first time the atmosphere of a super\-Earth [exoplanet](/wiki/Exoplanet "Exoplanet") was analyzed successfully.

In August 2016, astronomers announced the detection of *[Proxima b](/wiki/Proxima_b "Proxima b")*, an [Earth\-sized](/wiki/Terrestrial_planet "Terrestrial planet") [exoplanet](/wiki/Exoplanet "Exoplanet") that is in the [habitable zone](/wiki/Habitable_zone "Habitable zone") of the [red dwarf](/wiki/Red_dwarf "Red dwarf") [star](/wiki/Star "Star") [Proxima Centauri](/wiki/Proxima_Centauri "Proxima Centauri"), the closest star to the [Sun](/wiki/Sun "Sun"). Due to its closeness to [Earth](/wiki/Earth "Earth"), *Proxima b* may be a flyby destination for a fleet of interstellar *[StarChip](/wiki/StarChip_%28spacecraft%29 "StarChip (spacecraft)")* spacecraft currently being developed by the [Breakthrough Starshot](/wiki/Breakthrough_Starshot "Breakthrough Starshot") project.

#### 2018

In February 2018, K2\-141b, a rocky [ultra\-short period planet](/wiki/Ultra-short_period_planet "Ultra-short period planet") (USP) Super\-Earth, with a period of 0\.28 days orbiting the host star K2\-141 (EPIC 246393474\) was reported. Another Super\-Earth, [K2\-155d](/wiki/K2-155d "K2-155d"), is discovered.

In July 2018, the discovery of [40 Eridani](/wiki/HD_26965 "HD 26965") b was announced. At 16 light\-years it is the closest super\-Earth known, and its star is the second\-brightest hosting a super\-Earth.

#### 2019

In July 2019, the discovery of [GJ 357 d](/wiki/GJ_357_d "GJ 357 d") was announced. Thirty\-one light\-years from the Solar System, the planet is at least 6\.1 .

#### 2021

In 2021, the exoplanet [G 9\-40 b](/wiki/G_9-40_b "G 9-40 b") was discovered.

#### 2022

In 2022, the discovery of a super\-Earth around the red dwarf star [Ross 508](/wiki/Ross_508 "Ross 508") was reported. Part of the planet's [elliptical orbit](/wiki/Elliptical_orbit "Elliptical orbit") takes it within the [habitable zone](/wiki/Habitable_zone "Habitable zone").

#### 2024

On 31 January 2024 [NASA](/wiki/NASA "NASA") reported the discovery of a super\-Earth called TOI\-715 b located in the [habitable zone](/wiki/Habitable_zone "Habitable zone") of a red dwarf star about 137 light\-years away.


Is Proxima b an Earth-sized exoplanet?