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Exoplanetary Scratchpad

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Planets considered potentially habitable. Usually reside in the habitable zone and thought to have an appropriate mass. A list is maintained in the Potentially Habitable Index.

Potentially Habitable Planets Web Pages[]

Potentially Habitable Planets In the News[]

Seven Potentially Habitable Planets at One Year Anniversary of PHP Catalog (Dec 2012)[]

Potentially Habitable Planets[]

Ranked by Earth Similarity Index (Wikipedia) - Habitable Exoplanet Catalog Top 10:

  • Solar System (Earth = 1.0, Mars = 0.66) - Our home star system. Contains 4 terrestrial planets, 4 gas giant planets, several dwarf planets, an asteroid belt, and a kuiper belt, around a G-Class yellow dwarf star. Contains the only known habitable planet, Earth.
  • Kepler-438 System (b = 0.88) - Orange dwarf with a potentially habitable planet in it. This planet currently ranks highest on the Earth Similarity Index and is the smallest PHP known (1.1 RE).
  • Kepler-296 System (e = 0.85) - Red dwarf with a potentially habitable earth-sized planet. This planet currently has the highest earth-similarity index for planets around a red dwarf.
  • Gliese 667 System (Cc = 0.84, f = 0.76, e = 0.60) - MLO 4 is most commonly known as Gliese 667 and also known as HR 6426 and HD 156384. A triple star system 23 light years away that contains planets in Scorpius. It was first cataloged as a binary star by astronomers at the old Melbourne Observatory (MLO) in Australia in 1867, so it was cataloged as MLO 4. It consisting of binary of orange dwarf stars about 12 AU apart (ranging from 5 to 20 AU), around which a distant red Dwarf C orbits (ranging from 56 to 215 AU). Star C is a dynamically packed planetary system, with at up to 7 unconfirmed super-Earth planets. The system became the nearest multistar system with planets when planet b (innermost, largest), a temperate super Earth planet (5.7 ME, 0.05 AU) was discovered, and is at the very inner edge of the most generous habitable zone. It became the poster child for an announcement of 32 exoplanets discovered by European astronomers working on the HARPs project and brought the total number of exoplanets to near 400. Planet c was later discovered near the inner edge of least generous habitable zone and is about the same size, and receives the same amount of stellar energy as the Earth. It was calculated that it likely no longer has a magnetic field that could protect its oceans from stellar radiation. Planets f and e were confirmed and also orbit in the Hz further out. Planet d is just beyond he HZ. Outermost planet, g (2.4 ME) is likely a frozen planet and the only one beyond Mercury-like distances. The multi-planet solution is somewhat lax and complicated and may need further confirmation. An even more unconfirmed planet h may be between b and c. A fourth stellar companion D is not gravitationally bound to the system.
  • Kepler-422 System (b = 0.84) - Orange dwarf with a potentially habitable earth-sized planet.
  • Kepler-62 System (g = 0.83, f = 0.73) - A five planet system found by Kepler that contains two of the most Earth-like candidates. The star is somewhat cooler than the Sun (K class) and 1200 ly away in Lyra and older (7.4 BY). All planets were discovered at the same time. Planet b is 0.05AU and 1.3RE, c is 0.1AU and 0.54 RE, and d is 0.12 AU and 2.0 RE . Planet e is 60% larger than Earth and on the inner edge of the habitability zone (0.42 AU), and for a time had the highest Earth-Similarity Index. Planet f is 40% larger than Earth and in the middle of the habitable zone (0.7 AU). It is not known what effect not having a Jupiter-like planet would have on the habitability of this system.
  • Gliese 832 System () - CD-49°13515 is most commonly known as Gl 832, and also L 354-89, DM-49°13515, and HD 204961. It is the third nearest red dwarf with planets and in the constellation Indus. It can be considered a miniature version of the Solar System, with a large gaseous planet in a far orbit, and a smaller potentially rocky planet interior. Has a slightly eccentric Jovian planet with 64% Jupiter's mass at an asteroid-belt like distance. The planet has the second largest angular separation from it star of any known planets and is further from its star than any other red dwarf orbiting planet. A good astrometry detection candidate and a target for SIM. One of the larger red dwarf planets around one of the larger (M1.5) red dwarves (about half a Solar Mass). It also emits x-rays. Super Earth planet c is the most Earth-like known exoplanet, and one of the top three potentially habitable planets, but is more likely a super Venus. A third Earth-sized planet could exist between these planets.
  • EPIC 201367065 System () - Nearby red dwarf with a three transiting super Earths found by Kepler during its repurposed mission. The first two are scorching, but the third may be in the habitable zone. The closest transiting planets found that were luke-warm. The outermost is the nearest transiting potentially habitable planet. It is the smallest, yet most massive of the three (11.1 ME and 1.6 RE), classifying it as a Mega Earth.
  • Kepler-283 System () - Orange dwarf with a potentially habitable super Earth.
  • Tau Ceti System* (e = 0.77) - Tau Ceti is also known as HD 10700, HR 509, and Gl 71. The nearest single G-class yellow dwarf to the sun, somewhat smaller than the Sun. A popular science fiction subject and one of two targets of SETI-forerunner Project Ozma in the 1960s. Despite being somewhat older than the sun, it has an extensive asteroid and/or comet field 10-50 AU, with the bulk between 35 and 50 AU. It has about ten times as much material as the Sun. This would make life difficult. It is a metal deficient star, so it is thought less likely to host rocky planets. Traditional dopplar spectrometry has ruled out any large Jupiter sized planets at Jupiter like distances or closer in, which was thought to be good for any potentially habitable planets. Five candidate rocky super Earth planets were detected though using a new method of planetary detection. This method made predictions of the stellar "noise" activity that might obscure detection of a planet based on the long history of dopplar measurements done on this system. Deviations from this prediction pointed towards the existence of planets. Confirmation using more established methods is needed. These planets are labeled b through f as you go outward, span 0.1 AU to 1.35 AU, and get larger the further you go out (at least 2 ME to 6.6 ME). The outermost two are near the habitable zone and were originally hailed as possibly being the nearest and smallest known habitable planets. More recent modeling indicates they are not actually habitable though. Planet e is probably too close to the star and only in the HZ if generous assumptions are made. Planet f has probably only been in the habitable zone for about a billion years as a result of its star becoming hotter, which might make biosigns difficult to detect from Earth, considering it took 2 BY for biosigns to become detectable around the Earth. Since the star has a higher magnesium to silicon ratio than the Sun, these planets compositions could be quite different that the Solar System's. The lower mantles could be dominated with ferropericlase, which is not very viscious, which may make the rocks of the mantle flow easier than on Earth, affecting volcanism and tectonics. One of 5 PICTURE-C targets selected for sub-orbital coronograph observation.
  • Gliese 180 System - Red dwarf with a potentially habitable super Earth.


  • Gliese 581 System* (g = 0.82, d = 0.53) - BD-11°3759 is better known as Gliese 581. Small nearby Red Dwarf with six planets in tight circular orbits. Several planets were announced in the habitable zone, but have since been retracted due to being due to sunspots rotating in view during it's 130 day rotation. E is the smallest known dopplar-detected exoplanet and a Super Mercury, b is a hot Neptunian, c is a super-Venus and the first detected in the HZ (initially heralded as habitable, but later thought too hot due to the greenhouse effect). G (1/4 stellar rotation) was the most controversial heralded as the first habitable Super-Earth and "Eyeball Earth", but was disproven. D (1/2 stellar rotation) was later thought to be an even more promising planet for life as it was big enough for a decent greenhouse effect even though it was at the outer edge of the habitable zone, was later thought to also not exist, but then its existence was re-affirmed. F was thought to be a cold super-Earth, but also disproven. The star is not very active. A massive Kuiper Belt was found, which may have been allowed to exist because the system lacks a Jovian class planet. A further out Neptunian may be responsible for the cometary collisions that produced the debris.
  • Kepler-22 System (b = 0.75) - Contains the smallest planet in the habitable zone around a star at the time of its discovery by Kepler. The first around a sun-like star at Earth-like distances that is not probably tidally locked. The first potentially habitable planet confirmed (transits confirmed on other telescopes). Orbits around a sun-like star about every 290 days. It is about 2.4 times the radius of Earth and most likely gaseous. Its mass is difficult to measure and may be beyond the ability of modern telescopes (Keck will give it a try), so it has not been confirmed to be rocky yet (some planets the same size are either). A new technique determining mass from atmospheric pressure may one day help nail down its mass. It was the first of 54 habitable zone planet candidates to be independently confirmed. Depicted in art as blue with green clouds, the Scientific Exoplanets Renderer did not compute that it was habitable though. Its surface temperature is 76F, similar to a spring day on Earth. Searches for a potentially habitable moon, which it was predicted to be a good candidate for, have not found anything.
  • Gliese 163 System (c = 0.74) - A nearby red dwarf system 50 light years containing three planets, including one potentially habitable one. The innermost planet b is a Hot Jovian with a third of Jupiter's mass (have some data discrepancy, Extrasolar Planet Encyclopedia says 0.35 Jupiter Mass, 0.6 day period, Wikipedia says 9 days. The latter is more likely since it's not acknowledged as a Hot Jupiter around a Red Dwarf.). The potentially habitable planet c is 7 Earth masses large and receives 30-40% more radiation than the Earth does, on the inner edge of the habitability zone. It is thought to be unlikely that any runaway greenhouse gas would heat it up beyond habitability. It is the fifth most similar exoplanet of the six known potentially habitable exoplanets known at the time of its discovery. Likely too hot for most organisms, but some extremophiles may flourish on it. Its composition is unknown, but it is thought to be a mixture of rock and ice. There's a possibility of an outermost planet with 20 times Earth's mass much further out with a period of 669 days.
  • Kepler-61 System (b = 0.73) - Contains a Kepler discovered planet ranked at one time as having the 8th highest Earth Similarity Index. Has a radius of slightly more than 2 Earth's. It is located in the inner part of empirical habitable zone, a zone where liquid water could exist with high albedo, relatively low humidity and higher atmospheric pressure.

Off Ranking Chart

  • HD 40307 System (g = 0.79) - A bright orange dwarf star with six known non-transiting super-Earth planets, including one of the most potentially habitable planets known. The star is about the same age as the Sun and is not magnetically active. The first three were announced with 45 other HARPS detected by Swiss team who discovered 51 Pegasus as part of the HARPs project. Early dynamic studies suggested these were smaller versions of Neptune, rather than larger versions of Earth. The next three were found by another team using a new method with existing data that threw out unreliable data. The inner 5 planets range from epistellar distances to half Mercury's distance. The outermost planet g orbits at Venus-like distances and is well within the habitable zone. It has a minimum of 7 times Earth's mass and receives 62% of the radiation Earth does. Liquid water could exist on the surface if it proves to be rocky. Unlike many other potentially habitable planets, it is not tidally locked. It is also by far the nearest potentially habitable planet around a sun-like star. It is a good future target for direct imaging. It was calculated that the planet might still have a magnetic field just barely strong enough to shield it from stellar radiation to protect its ocean.
  • HD 85512 System (b = 0.77) - Also known as HD 85512, contains the second of three confirmed potentially habitable planet as of 2011. One of over 50 exoplanets and 16 Super-Earths discovered by HARPS at the ESO using the radial velocity method. It is about 3.6 Earth Masses at the inner edge of the habitable zone. The smallest exoplanet yet found potentially in the habitable zone when discovered. It could be between 85 to 120F. It could be habitable if it exhibited more than 50% cloud cover. It was rendered by the Scientific Exoplanet Renderer.

(*) Unconfirmed Planet Candidates on list


  • KOI-172 System - Kepler-69, also known as 2MASS J19330262+4452080 and KOI-172, is a sun-like star a little dimmer and about a billion years older. The inner planet b is a hot super-Earth. Initially, planet c was thought to be the most Earth-like planet detected, and heralded as the first Super-Earth found in the habitable zone by Kepler around a sunlike star (candidacy announced with a batch of 461 candidates found in 2013). It is now thought to be more likely interior to the habitable zone, a "Super Venus", is 70% larger than Earth, and has a Venus-like period of 242 days.

See Also[]