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114-412: K2-138 is notable for its large number of planets, all found through the efforts of citizen scientists. They are designated K2-138b , c , d , e , f , and g in order from their host star. The first five were validated by Christiansen et al., while K2-138g was noted as being a likely candidate. However, since there were only two transits of it, K2-138g could not be validated. There was a possibility that

228-400: A binary star system, and several circumbinary planets have been discovered which orbit both members of a binary star. A few planets in triple star systems are known and one in the quadruple system Kepler-64 . In 2013, the color of an exoplanet was determined for the first time. The best-fit albedo measurements of HD 189733b suggest that it is deep dark blue. Later that same year,

342-616: 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 the 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 method by the HARPS (High Accuracy Radial Velocity Planet Searcher) in Chile . In addition,

456-499: A pulsar planet in orbit around PSR 1829-10 , using pulsar timing variations. The claim briefly received intense attention, but Lyne and his team soon retracted it. As of 24 July 2024, a total of 5,787 confirmed exoplanets are listed in the NASA Exoplanet Archive, including a few that were confirmations of controversial claims from the late 1980s. The first published discovery to receive subsequent confirmation

570-510: A runaway greenhouse effect like Venus. Two further possible 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. 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. This planet has approximately 3.3 Earth masses and orbits

684-416: A G2-type star. On 6 September 2018, NASA discovered an exoplanet about 145 light years away from Earth in the constellation Virgo. This exoplanet, Wolf 503b, is twice the size of Earth and was discovered orbiting a type of star known as an "Orange Dwarf". Wolf 503b completes one orbit in as few as six days because it is very close to the star. Wolf 503b is the only exoplanet that large that can be found near

798-406: 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. Discovered on 5 January 2010, a planet HD 156668 b with a minimum mass of 4.15 Earth masses ,

912-437: A composition more similar to their host star than accretion-formed planets, which would contain increased abundances of heavier elements. Most directly imaged planets as of April 2014 are massive and have wide orbits so probably represent the low-mass end of a brown dwarf formation. One study suggests that objects above 10   M Jup formed through gravitational instability and should not be thought of as planets. Also,

1026-456: 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. 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. At 17 Earth masses, it

1140-485: 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 —

1254-498: A diversity of compositions that is not well-explained by a single mass-radius relation as that found in rocky planets). 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

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1368-408: A gaseous protoplanetary disk , they accrete hydrogen / helium envelopes. These envelopes cool and contract over time and, depending on the mass of the planet, some or all of the hydrogen/helium is eventually lost to space. This means that even terrestrial planets may start off with large radii if they form early enough. An example is Kepler-51b which has only about twice the mass of Earth but

1482-401: A large fraction of volatiles by volume overlying a rocky core. 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). Additional studies, conducted with lasers at

1596-580: 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

1710-399: A period of 0.28 days orbiting the host star K2-141 (EPIC 246393474) was reported. Another Super-Earth, K2-155d , is discovered. In July 2018, the discovery of 40 Eridani 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. In July 2019, the discovery of GJ 357 d was announced. Thirty-one light-years from

1824-623: 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 . On 2 February,

1938-425: A planet may be able to be formed in their orbit. In the early 1990s, a group of astronomers led by Donald Backer , who were studying what they thought was a binary pulsar ( PSR B1620−26 b ), determined that a third object was needed to explain the observed Doppler shifts . Within a few years, the gravitational effects of the planet on the orbit of the pulsar and white dwarf had been measured, giving an estimate of

2052-505: A potentially habitable super-Earth HD 85512 b was found using the HARPS as well as a three super-Earth system 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

2166-411: A red dwarf star about 137 light-years away. 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 envelopes without well-defined rocky or watery surfaces; that is, they are either gas giants or ice giants , not terrestrial planets. In January 2016,

2280-409: A significant effect. There is more thermal emission than reflection at some near-infrared wavelengths for massive and/or young gas giants. So, although optical brightness is fully phase -dependent, this is not always the case in the near infrared. Temperatures of gas giants reduce over time and with distance from their stars. Lowering the temperature increases optical albedo even without clouds. At

2394-451: A statistical technique called "verification by multiplicity". Before these results, most confirmed planets were gas giants comparable in size to Jupiter or larger because they were more easily detected, but the Kepler planets are mostly between the size of Neptune and the size of Earth. On 23 July 2015, NASA announced Kepler-452b , a near-Earth-size planet orbiting the habitable zone of

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2508-469: 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

2622-608: A system is designated "b" (the parent star is considered "a") and later planets are given subsequent letters. If several planets in the same system are discovered at the same time, the closest one to the star gets the next letter, followed by the other planets in order of orbital size. A provisional IAU-sanctioned standard exists to accommodate the designation of circumbinary planets . A limited number of exoplanets have IAU-sanctioned proper names . Other naming systems exist. For centuries scientists, philosophers, and science fiction writers suspected that extrasolar planets existed, but there

2736-463: A true temperature of 737 K (464 °C or 867 °F ). 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), giving it a lower black body temperature than the more absorbent (lower albedo ) Earth. Earth's magnetic field results from its flowing liquid metallic core, but in super-Earths

2850-533: 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 kelvin and be too hot to support liquid water. 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 , both on the edge of the habitable zone around

2964-412: A watery and icy planet. Within this range of radii the super-Earth Gliese 876 d would have a surface gravity between 1.9 g and 3.3g (19 and 32 m/s ). 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

3078-474: A wide range of other factors in determining the suitability of a planet for hosting life. Rogue planets are those that do not orbit any star. Such objects are considered a separate category of planets, especially if they are gas giants , often counted as sub-brown dwarfs . The rogue planets in the Milky Way possibly number in the billions or more. The official definition of the term planet used by

3192-505: Is a planet outside the Solar System . The first possible evidence of an exoplanet was noted in 1917 but was not then recognized as such. The first confirmation of the detection occurred in 1992. A different planet, first detected in 1988, was confirmed in 2003. As of 7 November 2024, there are 5,787 confirmed exoplanets in 4,320 planetary systems , with 969 systems having more than one planet . The James Webb Space Telescope (JWST)

3306-410: Is a type of exoplanet 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. 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

3420-529: Is almost the size of Saturn, which is a hundred times the mass of Earth. Kepler-51b is quite young at a few hundred million years old. There is at least one planet on average per star. About 1 in 5 Sun-like stars have an "Earth-sized" planet in the habitable zone . Most known exoplanets orbit stars roughly similar to the Sun , i.e. main-sequence stars of spectral categories F, G, or K. Lower-mass stars ( red dwarfs , of spectral category M) are less likely to have planets massive enough to be detected by

3534-547: Is an extension of the system used for designating multiple-star systems as adopted by the International Astronomical Union (IAU). For exoplanets orbiting a single star, the IAU designation is formed by taking the designated or proper name of its parent star, and adding a lower case letter. Letters are given in order of each planet's discovery around the parent star, so that the first planet discovered in

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3648-408: Is expected to discover more exoplanets, and to give more insight into their traits, such as their composition , environmental conditions , and potential for life . There are many methods of detecting exoplanets . Transit photometry and Doppler spectroscopy have found the most, but these methods suffer from a clear observational bias favoring the detection of planets near the star; thus, 85% of

3762-467: Is in fact much larger and hotter than first reported. 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." 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,

3876-707: Is not known why TrES-2b is so dark—it could be due to an unknown chemical compound. For gas giants , geometric albedo generally decreases with increasing metallicity or atmospheric temperature unless there are clouds to modify this effect. Increased cloud-column depth increases the albedo at optical wavelengths, but decreases it at some infrared wavelengths. Optical albedo increases with age, because older planets have higher cloud-column depths. Optical albedo decreases with increasing mass, because higher-mass giant planets have higher surface gravities, which produces lower cloud-column depths. Also, elliptical orbits can cause major fluctuations in atmospheric composition, which can have

3990-510: Is now clear that hot Jupiters make up the minority of exoplanets. In 1999, Upsilon Andromedae became the first main-sequence star known to have multiple planets. Kepler-16 contains the first discovered planet that orbits a binary main-sequence star system. On 26 February 2014, NASA announced the discovery of 715 newly verified exoplanets around 305 stars by the Kepler Space Telescope . These exoplanets were checked using

4104-472: Is the least massive planet detected by the 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 , one of which, although not yet confirmed, has an estimated minimum mass of 1.35 ± 0.23 times that of Earth, which would be

4218-585: Is too massive to be a planet and might be a brown dwarf . Known orbital times for exoplanets vary from less than an hour (for those closest to their star) to thousands of years. Some exoplanets are so far away from the star that it is difficult to tell whether they are gravitationally bound to it. Almost all planets detected so far are within the Milky Way. However, there is evidence that extragalactic planets , exoplanets located in other galaxies, may exist. The nearest exoplanets are located 4.2 light-years (1.3 parsecs ) from Earth and orbit Proxima Centauri ,

4332-452: 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. 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) M E with a mean density of 3.14 g/cm . Instead of a primarily rocky composition,

4446-564: The ESO 3.6 m Telescope . With a Bayesian analysis of the K2 photometry and HARPS radial-velocities ( RVs ) the team were able to constrain the mass of planet b to e. The bulk densities of the planets range from Earth-like density for planet b to Neptune-like density for planet e. The masses and densities constrain the composition of the planets. They have likely rocky cores and a substantial atmospheric layer, composed of volatiles. For planets f and g this team

4560-408: The International Astronomical Union (IAU) only covers the Solar System and thus does not apply to exoplanets. The IAU Working Group on Extrasolar Planets issued a position statement containing a working definition of "planet" in 2001 and which was modified in 2003. An exoplanet was defined by the following criteria: This working definition was amended by the IAU's Commission F2: Exoplanets and

4674-737: 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). 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] A more recent study found that one of these candidates (KOI 326.01)

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4788-445: 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 the Sun in the habitable zone and possibly a "prime candidate to host alien life ". 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

4902-502: 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. 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. If

5016-808: The Lawrence Livermore National Laboratory and 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. 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

5130-457: The Milky Way galaxy . Planets are extremely faint compared to their parent stars. For example, a Sun-like star is about a billion times brighter than the reflected light from any exoplanet orbiting it. It is difficult to detect such a faint light source, and furthermore, the parent star causes a glare that tends to wash it out. It is necessary to block the light from the parent star to reduce

5244-546: The Mount Wilson Observatory , produced a spectrum of the star using Mount Wilson's 60-inch telescope . He interpreted the spectrum to be of an F-type main-sequence star , but it is now thought that such a spectrum could be caused by the residue of a nearby exoplanet that had been pulverized by the gravity of the star, the resulting dust then falling onto the star. The first suspected scientific detection of an exoplanet occurred in 1988. Shortly afterwards,

5358-580: The Observatoire de Haute-Provence , ushered in the modern era of exoplanetary discovery, and was recognized by a share of the 2019 Nobel Prize in Physics . Technological advances, most notably in high-resolution spectroscopy , led to the rapid detection of many new exoplanets: astronomers could detect exoplanets indirectly by measuring their gravitational influence on the motion of their host stars. More extrasolar planets were later detected by observing

5472-479: 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

5586-543: The radial-velocity method . Despite this, several tens of planets around red dwarfs have been discovered by the Kepler space telescope , which uses the transit method to detect smaller planets. Using data from Kepler , a correlation has been found between the metallicity of a star and the probability that the star hosts a giant planet, similar to the size of Jupiter . Stars with higher metallicity are more likely to have planets, especially giant planets, than stars with lower metallicity. Some planets orbit one member of

5700-454: The sin i ambiguity ." The NASA Exoplanet Archive includes objects with a mass (or minimum mass) equal to or less than 30 Jupiter masses. Another criterion for separating planets and brown dwarfs, rather than deuterium fusion, formation process or location, is whether the core pressure is dominated by Coulomb pressure or electron degeneracy pressure with the dividing line at around 5 Jupiter masses. The convention for naming exoplanets

5814-500: The 13-Jupiter-mass cutoff does not have a precise physical significance. Deuterium fusion can occur in some objects with a mass below that cutoff. The amount of deuterium fused depends to some extent on the composition of the object. As of 2011, the Extrasolar Planets Encyclopaedia included objects up to 25 Jupiter masses, saying, "The fact that there is no special feature around 13   M Jup in

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5928-534: 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. In 2011, a density of 55 Cancri e was calculated which turned out to be similar to Earth's. At

6042-581: The Solar System in August 2018. The official working definition of an exoplanet is now as follows: The IAU's working definition is not always used. One alternate suggestion is that planets should be distinguished from brown dwarfs on the basis of their formation. It is widely thought that giant planets form through core accretion , which may sometimes produce planets with masses above the deuterium fusion threshold; massive planets of that sort may have already been observed. Brown dwarfs form like stars from

6156-413: The Solar System's four inner planets, a new and significant discovery. 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. 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

6270-402: The Solar System, the planet is at least 6.1 M E . In 2021, the exoplanet G 9-40 b was discovered. In 2022, the discovery of a super-Earth around the red dwarf star Ross 508 was reported. Part of the planet's elliptical orbit takes it within the habitable zone . On 31 January 2024 NASA reported the discovery of a super-Earth called TOI-715 b located in the habitable zone of

6384-495: The Sun and are likewise accompanied by planets. In the eighteenth century, the same possibility was mentioned by Isaac Newton in the " General Scholium " that concludes his Principia . Making a comparison to the Sun's planets, he wrote "And if the fixed stars are the centres of similar systems, they will all be constructed according to a similar design and subject to the dominion of One ." In 1938, D.Belorizky demonstrated that it

6498-517: The Super-Earth GJ 1214 b ), 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. 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

6612-433: 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 ). 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

6726-446: The bulk composition of the super-Earths. A study on Gliese 876 d by a team around Diana Valencia 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

6840-450: 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 . 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 the Sun. "This planet probably does have liquid water," said David Charbonneau,

6954-409: The closest star to the Sun. The discovery of exoplanets has intensified interest in the search for extraterrestrial life . There is special interest in planets that orbit in a star's habitable zone (sometimes called "goldilocks zone"), where it is possible for liquid water, a prerequisite for life as we know it, to exist on the surface. However, the study of planetary habitability also considers

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7068-420: The colors of several other exoplanets were determined, including GJ 504 b which visually has a magenta color, and Kappa Andromedae b , which if seen up close would appear reddish in color. Helium planets are expected to be white or grey in appearance. The apparent brightness ( apparent magnitude ) of a planet depends on how far away the observer is, how reflective the planet is (albedo), and how much light

7182-522: 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 . 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. In February 2018, K2-141b, a rocky ultra-short period planet (USP) Super-Earth, with

7296-427: The direct gravitational collapse of clouds of gas, and this formation mechanism also produces objects that are below the 13   M Jup limit and can be as low as 1   M Jup . Objects in this mass range that orbit their stars with wide separations of hundreds or thousands of Astronomical Units (AU) and have large star/object mass ratios likely formed as brown dwarfs; their atmospheres would likely have

7410-462: The end result of slow, inward disk migration. Spitzer observations of K2-138g were announced on the AAS Meeting #233. The iPoster shows an updated radius of K2-138g of 3.7 R 🜨 , making it the largest planet in the system. This result was preliminary until being confirmed in February 2021. A team of astronomers collected 215 spectra over 79 nights with the instrument HARPS mounted on

7524-583: The existence of a dark body in the 70 Ophiuchi system with a 36-year period around one of the stars. However, Forest Ray Moulton published a paper proving that a three-body system with those orbital parameters would be highly unstable. During the 1950s and 1960s, Peter van de Kamp of Swarthmore College made another prominent series of detection claims, this time for planets orbiting Barnard's Star . Astronomers now generally regard all early reports of detection as erroneous. In 1991, Andrew Lyne , M. Bailes and S. L. Shemar claimed to have discovered

7638-461: 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. A refined model in 2019 constrains it to around five Earth masses; planets of this mass are probably mini-Neptunes. The fact that there are barely any asteroids or planetesimals inside

7752-410: The exoplanets are not tightly bound to stars, so they're actually wandering through space or loosely orbiting between stars. We can estimate that the number of planets in this [faraway] galaxy is more than a trillion." On 21 March 2022, the 5000th exoplanet beyond the Solar System was confirmed. On 11 January 2023, NASA scientists reported the detection of LHS 475 b , an Earth-like exoplanet – and

7866-449: The exoplanets detected are inside the tidal locking zone. In several cases, multiple planets have been observed around a star. About 1 in 5 Sun-like stars are estimated to have an " Earth -sized" planet in the habitable zone . Assuming there are 200 billion stars in the Milky Way , it can be hypothesized that there are 11 billion potentially habitable Earth-sized planets in the Milky Way, rising to 40 billion if planets orbiting

7980-414: The first confirmation of detection came in 1992 when Aleksander Wolszczan announced the discovery of several terrestrial-mass planets orbiting the pulsar PSR B1257+12 . The first confirmation of an exoplanet orbiting a main-sequence star was made in 1995, when a giant planet was found in a four-day orbit around the nearby star 51 Pegasi . Some exoplanets have been imaged directly by telescopes, but

8094-593: The first exoplanet discovered by the James Webb Space Telescope . This space we declare to be infinite... In it are an infinity of worlds of the same kind as our own. In the sixteenth century, the Italian philosopher Giordano Bruno , an early supporter of the Copernican theory that Earth and other planets orbit the Sun ( heliocentrism ), put forward the view that fixed stars are similar to

8208-580: The forces of magma to break the crust into plates. 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 into a planet composed mainly of rock with a thin atmosphere, the small rocky core remains engulfed by its large hydrogen-rich envelope. Theoretical models show that Hot Jupiters and Hot Neptunes can evolve by hydrodynamic loss of their atmospheres to Mini-Neptunes (as it could be

8322-431: The glare while leaving the light from the planet detectable; doing so is a major technical challenge which requires extreme optothermal stability . All exoplanets that have been directly imaged are both large (more massive than Jupiter ) and widely separated from their parent stars. Specially designed direct-imaging instruments such as Gemini Planet Imager , VLT-SPHERE , and SCExAO will image dozens of gas giants, but

8436-406: 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. On 25 June 2013, three "super Earth" planets have been found orbiting a nearby star at

8550-632: 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). 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

8664-572: The habitable zone, some around Sun-like stars. In September 2020, astronomers reported evidence, for the first time, of an extragalactic planet , M51-ULS-1b , detected by eclipsing a bright X-ray source (XRS), in the Whirlpool Galaxy (M51a). Also in September 2020, astronomers using microlensing techniques reported the detection , for the first time, of an Earth-mass rogue planet unbounded by any star, and free floating in

8778-410: The higher end of the mass scale, although " mini-Neptunes " is a more common term. In general, super-Earths are defined by their masses . The term does not imply temperatures, compositions, orbital properties, habitability, or environments. While sources generally agree on an upper bound of 10 Earth masses (~69% of the mass of Uranus , which is the Solar System's giant planet with the least mass),

8892-412: The host star. A process called photoevaporation . Planet f is possibly the most water-rich planet in the system, with an upper water-mass-fraction of 66%. The radius of planet g is larger than a planet with a water-rich composition and the researchers conclude that planet g has an atmosphere rich in hydrogen and helium and in this case the upper volatile-mass fraction would be only 5%. All planets of

9006-438: 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. 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

9120-414: The lower bound varies from 1 or 1.9 to 5, with various other definitions appearing in the popular media. 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). This definition was made by the Kepler space telescope personnel. Some authors further suggest that

9234-476: 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 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

9348-542: 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. That said, super-Earth magnetic fields are yet to be detected observationally. Exoplanet An exoplanet or extrasolar planet

9462-425: The mass of the third object that was too small for it to be a star. The conclusion that the third object was a planet was announced by Stephen Thorsett and his collaborators in 1993. On 6 October 1995, Michel Mayor and Didier Queloz of the University of Geneva announced the first definitive detection of an exoplanet orbiting a main-sequence star, nearby G-type star 51 Pegasi . This discovery, made at

9576-427: The more accurately determined mass of Kepler-10c suggests a world made almost entirely of volatiles, mainly water. 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;

9690-579: The nineteenth century. Some of the earliest involve the binary star 70 Ophiuchi . In 1855, William Stephen Jacob at the East India Company 's Madras Observatory reported that orbital anomalies made it "highly probable" that there was a "planetary body" in this system. In the 1890s, Thomas J. J. See of the University of Chicago and the United States Naval Observatory stated that the orbital anomalies proved

9804-535: The numerous red dwarfs are included. The least massive exoplanet known is Draugr (also known as PSR B1257+12 A or PSR B1257+12 b), which is about twice the mass of the Moon . The most massive exoplanet listed on the NASA Exoplanet Archive is HR 2562 b , about 30 times the mass of Jupiter . However, according to some definitions of a planet (based on the nuclear fusion of deuterium ), it

9918-496: The observed mass spectrum reinforces the choice to forget this mass limit". As of 2016, this limit was increased to 60 Jupiter masses based on a study of mass–density relationships. The Exoplanet Data Explorer includes objects up to 24 Jupiter masses with the advisory: "The 13 Jupiter-mass distinction by the IAU Working Group is physically unmotivated for planets with rocky cores, and observationally problematic due to

10032-557: The orbit of Mercury led some astronomers believing that a super-Earth might have formed in proximity to the Sun, cleared its neighborhood and rapidly get disrupted by the Sun. 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

10146-399: The parent star and form an unbroken chain of near-3:2 resonances . Their orbital periods range from 2.35 to 12.76 days, with the sixth planet orbiting much further out with a period of about 41 days. K2-138b, c, d, e, and f are locked in several chains of three-body resonances, a feat shared by only a handful of systems, including TRAPPIST-1 and Kepler-80 . Like the former, K2-138 could show

10260-556: The planet receives from its star, which depends on how far the planet is from the star and how bright the star is. So, a planet with a low albedo that is close to its star can appear brighter than a planet with a high albedo that is far from the star. The darkest known planet in terms of geometric albedo is TrES-2b , a hot Jupiter that reflects less than 1% of the light from its star, making it less reflective than coal or black acrylic paint. Hot Jupiters are expected to be quite dark due to sodium and potassium in their atmospheres, but it

10374-406: The planet's existence to be confirmed. On 9 January 1992, radio astronomers Aleksander Wolszczan and Dale Frail announced the discovery of two planets orbiting the pulsar PSR 1257+12 . This discovery was confirmed, and is generally considered to be the first definitive detection of exoplanets. Follow-up observations solidified these results, and confirmation of a third planet in 1994 revived

10488-563: The planets were initially unknown, as the data for K2-138 did not have a high enough signal-to-noise ratio for transit-timing variation (TTV) analysis. However, the Spitzer Space Telescope could be able to accurately detect TTVs and lead to the masses of the planets being calculated. Planets b through f are predicted to cause TTVs on the order of 2.5 to 7.1 minutes, for predicted masses between 4 M E and 7 M E . The five validated planets of K2-138 are very close to

10602-449: 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 it every three years. 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 that of

10716-449: The shortest orbit is HD 219134 b , and is Earth's closest known rocky, and transiting, exoplanet. 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. In August 2016, astronomers announced

10830-447: 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 . 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)

10944-574: The so-called small planet radius gap . The gap, sometimes called the Fulton gap, is the observation that it is unusual to find exoplanets with sizes between 1.5 and 2 times the radius of the Earth. In January 2020, scientists announced the discovery of TOI 700 d , the first Earth-sized planet in the habitable zone detected by TESS. As of January 2020, NASA's Kepler and TESS missions had identified 4374 planetary candidates yet to be confirmed, several of them being nearly Earth-sized and located in

11058-546: 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 considering 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

11172-644: The system likely have a less massive core compared to earth. K2-138 was selected as a target by ESA in the first Announcement of Opportunity (AO-1) Program of the CHEOPS mission , which was launched in December 2019. For 87.6 orbits the spacecraft will record the transits to measure TTVs of the planets. K2-138 could become a benchmark system to compare RV and TTV masses. The system is also a good candidate to search for co-orbital bodies , which are predicted to exist and to be stable in resonant chain systems like K2-138. Super-Earth A Super-Earth or super-terran

11286-553: 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. Planets above 10 Earth masses are termed massive solid planets , mega-Earths , or gas giant planets , depending on whether they are mostly made of rock and ice or mostly gas. The first super-Earths were discovered by Aleksander Wolszczan and Dale Frail around

11400-461: The third, Kepler-440b , is a super-Earth. 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

11514-460: The time, astronomers remained skeptical for several years about this and other similar observations. It was thought some of the apparent planets might instead have been brown dwarfs , objects intermediate in mass between planets and stars. In 1990, additional observations were published that supported the existence of the planet orbiting Gamma Cephei, but subsequent work in 1992 again raised serious doubts. Finally, in 2003, improved techniques allowed

11628-405: The topic in the popular press. These pulsar planets are thought to have formed from the unusual remnants of the supernova that produced the pulsar, in a second round of planet formation, or else to be the remaining rocky cores of gas giants that somehow survived the supernova and then decayed into their current orbits. As pulsars are aggressive stars, it was considered unlikely at the time that

11742-430: The two transits for this candidate were from two individual long-period planets. K2-138g was confirmed by follow-up studies in 2019 and 2021. All six planets are within the super-Earth and mini-Neptune categories, with radii between about 1.6 R 🜨 to 3.3 R 🜨 . The outer five, including K2-138g, are likely small gaseous worlds with no solid surface. However, the smaller K2-138b could be rocky. The masses of

11856-452: 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). 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

11970-440: The variation in a star's apparent luminosity as an orbiting planet transited in front of it. Initially, the most known exoplanets were massive planets that orbited very close to their parent stars. Astronomers were surprised by these " hot Jupiters ", because theories of planetary formation had indicated that giant planets should only form at large distances from stars. But eventually more planets of other sorts were found, and it

12084-521: The vast majority have been detected through indirect methods, such as the transit method and the radial-velocity method . In February 2018, researchers using the Chandra X-ray Observatory , combined with a planet detection technique called microlensing , found evidence of planets in a distant galaxy, stating, "Some of these exoplanets are as (relatively) small as the moon, while others are as massive as Jupiter. Unlike Earth, most of

12198-555: The vast majority of known extrasolar planets have only been detected through indirect methods. Planets may form within a few to tens (or more) of millions of years of their star forming. The planets of the Solar System can only be observed in their current state, but observations of different planetary systems of varying ages allows us to observe planets at different stages of evolution. Available observations range from young proto-planetary disks where planets are still forming to planetary systems of over 10 Gyr old. When planets form in

12312-408: The whole planet except for its core. 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. 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 . Since

12426-496: Was able to constrain the upper limit of the mass to 8.7 and 25.5 earth masses. A paper by Acuña et al. studied the water content of the K2-138 system, assuming a volatile layer constituted of water in steam and supercritical phases. They find that the planet b has an upper water-mass-fraction of 0.7% and is a volatile-poor planet. Planet b could have formed with a thick water atmosphere that was blown away by XUV -radiation coming from

12540-401: Was included in a paper published on 21 November 2011. More detailed data on Gliese 667 Cc were published in early February 2012. In September 2012, the discovery of two planets orbiting Gliese 163 was announced. 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 . On 7 January 2013, astronomers from

12654-478: Was itself a "borderline" case, just barely large enough to sustain plate tectonics. These findings were corroborated by van Heck et al., who determined that plate tectonics may be more likely on super-Earths than on Earth itself, assuming similar composition. However, other studies determined 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

12768-473: Was made in 1988 by the Canadian astronomers Bruce Campbell, G. A. H. Walker, and Stephenson Yang of the University of Victoria and the University of British Columbia . Although they were cautious about claiming a planetary detection, their radial-velocity observations suggested that a planet orbits the star Gamma Cephei . Partly because the observations were at the very limits of instrumental capabilities at

12882-417: Was no way of knowing whether they were real in fact, how common they were, or how similar they might be to the planets of the Solar System . Various detection claims made in the nineteenth century were rejected by astronomers. The first evidence of a possible exoplanet, orbiting Van Maanen 2 , was noted in 1917, but was not recognized as such. The astronomer Walter Sydney Adams , who later became director of

12996-469: Was realistic to search for exo-Jupiters by using transit photometry . In 1952, more than 40 years before the first hot Jupiter was discovered, Otto Struve wrote that there is no compelling reason that planets could not be much closer to their parent star than is the case in the Solar System, and proposed that Doppler spectroscopy and the transit method could detect super-Jupiters in short orbits. Claims of exoplanet detections have been made since

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