Short description: Mini-Neptune orbiting K2-288B K2-288Bb[1][2] Artist’s impression of K2-288Bb orbiting its host star K2-288B, with the primary star K2-288A in the top left corner Discovery Discovery date| 7 January 2019[1] Orbital characteristics Semi-major axis | 0.164 (±0.03)[2] AU Orbital period| 31.393463 +0.000067−0.000069[2] d Inclination| 89.81 +0.13−0.17[2] Star| K2-288B Physical characteristics Mean radius| 1.90 (±0.3)[2] R⊕ Physics| 226.36 (±22.3) K (−46.79 °C; −52.22 °F)[2] K2-288Bb (previously designated EPIC 210693462 b) is a super-Earth or mini-Neptune exoplanet orbiting in the habitable zone of K2-288B, a low-mass M-dwarf star in a binary star system in the constellation of Taurus about 226 light-years from Earth.[1][2][3] It was discovered by citizen scientists while analysing data from the Kepler spacecraft's K2 mission, and was announced on 7 January 2019.[1][2] K2-288 is the third transiting planet system identified by the Exoplanet Explorers program, after the six planets of K2-138 and the three planets of K2-233.[2] K2-288Bb is likely to be in the habitable zone of its host star, and thus may be capable on supporting life, though the planet's composition is unknown. ## Contents * 1 Discovery * 2 Characteristics * 2.1 Mass, radius, and temperature * 2.2 Orbit and rotation * 2.3 Host stars * 3 Potential habitability * 4 See also * 5 References * 6 External links ## Discovery K2-288 was observed by the Kepler space telescope during Campaign 4 of its extended K2 "Second Light" mission, lasting from April through September 2015. A group of astronomers looked through this data to try and find transiting exoplanets. However, because of Kepler's decreased stability after the failure of two reaction wheels, the start of each campaign had extreme systematic errors, and these few days of data were discarded by the team. For K2-288, they only found two transits in the remaining data, not enough to merit follow-up studies. As a result, this system was pushed aside for more convincing candidates.[4] After the first analysis, the same team used better methods to model the systematic errors caused by K2 and re-processed all the Campaign 4 data they had. However, instead of looking through it all again by eye, they decided to upload it to the new Zooniverse project Exoplanet Explorers in April 2017. Among other systems like K2-138, citizen scientists also spotted three transits of the red dwarf star EPIC 210693462. Several volunteers started a lengthy discussion thread about the system, concluding that, with the current transit and stellar parameters, the planet candidate was very similar in both size and temperature to Earth. This caught the attention of the original team of astronomers and another at NASA Goddard who independently found the three transits at the same time, and follow-up observations were started.[4] The group, led by Adina Feinstein, started by obtaining spectra of the star using the Keck Observatory in Hawaii, where they noticed that there was a secondary companion star. This meant there was a possibility that the second star was creating the transit signal, and it wasn't a real planet. However, the team concluded that it was far more likely to be an exoplanet and not a false positive. They used data from Kepler, as well as a transit observed by the Spitzer Space Telescope, to determine which star the planet orbited. Observations and modelling suggested the transit data was most compatible with the planet transiting the smaller, secondary star. The team was then able to calculate the radius, orbit, and temperature of the planet, and they announced their results at the 233rd American Astronomical Society meeting in Seattle on January 7, 2019.[4] ## Characteristics ### Mass, radius, and temperature K2-288Bb is unusual for having a radius not commonly seen among most exoplanets. At 1.90 R⊕, it falls within the so-called Fulton Gap between 1.5 and 2.0 R⊕. This is the range of sizes where rocky super-Earths start to accumulate thick volatile layers and turn into mini-Neptunes.[2] Planets in the middle of this gap are uncommon, and as such, not much is known about them. K2-288Bb could either be a low-density mini-Neptune like GJ 9827 d, or a large rocky super-Earth like LHS 1140 b.[1] Its mass is currently unknown and would require additional studies using the Radial velocity method to be determined. Based on its size, K2-288Bb is probably still undergoing atmospheric evolution and/or erosion. The planet is also orbiting in or near the habitable zone of K2-288B, where temperatures are just right for a planet to host liquid water with the right atmosphere. K2-288 Bb has an equilibrium temperature of 226.36 K (−46.79 °C; −52.22 °F) (lower than Earth's 255 K (−18 °C; −1 °F)) and receives less sunlight than Earth.[2] ### Orbit and rotation K2-288Bb has a close orbit around the second, smaller star of the binary system. It orbits every 31.393 days at a distance of about 0.164 AU. For comparison, the Earth's Solar System's innermost planet, Mercury, orbits every 88 days at 0.38 AU. However, due to the small size of the host star, K2-288Bb is well within the habitable zone. In the unlikely possibility that the planet orbits the primary, it would have a semi-major axis of 0.231 AU and still reside in the habitable zone.[2] K2-288Bb is probably tidally locked regardless of which star it orbits; one side of the planet would permanently face the host, while the other side would be always facing away. ### Host stars K2-288Bb is within a binary system of two red dwarfs. The primary, K2-288A, is 52% the mass and 45% the radius of the Sun, while the secondary, K2-288B, is 33% the mass and 32% the radius. They are both much cooler and dimmer than the Sun, with temperatures of 3584 K and 3341 K, and are 0.03236 and 0.01175 times as luminous as the Sun, which has a temperature of 5772 K. Both stars are also rather metal-poor, with metallicities of -0.29 [Fe/H] for the primary, and -0.21 [Fe/H] for the secondary.[2] In comparison, the Sun has a metallicity of 0.00 [Fe/H]. K2-288A and K2-288B orbit each other at a distance of about 55 AU, around six times the distance from Saturn to the Sun.[2] ## Potential habitability It is unknown if K2-288Bb is capable of supporting life. On one hand, it is likely well within the habitable zone of its star, with a temperate equilibrium temperature of about 226 K. However, because of its radius within the Fulton Gap, there is significant uncertainty in its composition. K2-288Bb could be a potentially habitable rocky or water-rich world, but it might also be a hostile gas planet.[4] ## See also * Kepler-296f, another temperate planet in a binary system with a radius inside the Fulton gap * K2-138 * List of exoplanet extremes * List of potentially habitable exoplanets ## References 1. ↑ 1.0 1.1 1.2 1.3 1.4 Hawkes, Alison; Cofield, Calia; Reddy, Francis (7 January 2019). "Citizen Scientists Find New World with NASA Telescope". NASA. https://www.jpl.nasa.gov/news/news.php?feature=7313. 2. ↑ 2.00 2.01 2.02 2.03 2.04 2.05 2.06 2.07 2.08 2.09 2.10 2.11 2.12 2.13 Feinstein, Adina D. (7 January 2019). "K2-288Bb: A Small Temperate Planet in a Low-mass Binary System Discovered by Citizen Scientists". The Astronomical Journal 157 (2): 40. doi:10.3847/1538-3881/aafa70. Bibcode: 2019AJ....157...40F. https://dspace.mit.edu/bitstream/1721.1/121222/1/Feinstein_2019_AJ_157_40.pdf. 3. ↑ Mack, Eric (9 January 2019). "NASA's Kepler helps amateurs spot unusual new planet in 'Goldilocks zone'". CNET. https://www.cnet.com/news/nasa-kepler-helps-amateurs-spot-unusual-new-planet-in-goldilocks-zone/. 4. ↑ 4.0 4.1 4.2 4.3 Feinstein, Adina (7 January 2019). "Exoplanet Explorers Discoveries - A Small Planet In The Habitable Zone". Zooniverse.org. https://blog.zooniverse.org/2019/01/07/exoplanet-explorers-discoveries-the-habitable-zone-planet-k2-288bb/. ## External links * Taurus Constellation at Constellation Guide * The Deep Photographic Guide to the Constellations: Taurus * v * t * e Exoplanetology * Planet * Definition * IAU * Planetary science Main topics| * Exoplanet * Methods of detecting exoplanets * Planetary system Sizes and types| | Terrestrial| * Carbon planet * Coreless planet * Desert planet * Dwarf planet * Ice planet * Iron planet * Lava planet * Mega-Earth * Ocean planet * Sub-Earth * Super-Earth | Gaseous| * Eccentric Jupiter * Gas dwarf * Helium planet * Hot Jupiter * Hot Neptune * Ice giant * Mini-Neptune * Super-Neptune * Super-Jupiter Other types| * Brown dwarf * Chthonian planet * Circumbinary planet * Disrupted planet * Double planet * Eyeball planet * Mesoplanet * Planemo * Planet/Brown dwarf boundary * Planetesimal * Protoplanet * Pulsar planet * Sub-brown dwarf * Ultra-cool dwarf * Ultra-short period planets (USP) Formation and evolution| * Accretion * Accretion disk * Asteroid belt * Circumplanetary disk * Circumstellar disc * Circumstellar envelope * Cosmic dust * Debris disk * Detached object * Disrupted planet * Excretion disk * Exoplanetary Circumstellar Environments and Disk Explorer * Exozodiacal dust * Extraterrestrial materials * Extraterrestrial sample curation * Giant-impact hypothesis * Gravitational collapse * Hills cloud * Interplanetary dust cloud * Interplanetary medium * Interplanetary space * Interstellar cloud * Interstellar dust * Interstellar medium * Interstellar space * Kuiper belt * List of interstellar and circumstellar molecules * Merging stars * Molecular cloud * Nebular hypothesis * Oort cloud * Outer space * Planetary migration * Planetary system * Planetesimal * Planet formation * Protoplanetary disk * Ring system * Rubble pile * Sample-return mission * Scattered disc * Star formation Systems| * Exocomet * Exomoon * Interstellar comet * Mean-motion resonances * Retrograde planet * Rogue planet * Tidally detached exomoon * Titius–Bode laws * Trojan planet Host stars| * A * B * Binary star * Brown dwarfs * Extragalactic planet * F/Yellow-white dwarfs * G/Yellow dwarfs * Herbig Ae/Be * K/Orange dwarfs * M/Red dwarfs * Planets in globular clusters * Pulsar * Red giant * Subdwarf B * Subgiant * T Tauri * White dwarfs * Yellow giants Detection| * Astrometry * Direct imaging * list * Microlensing * list * Polarimetry * Pulsar timing * list * Radial velocity * list * Transit method * list * Transit-timing variation Habitability| * Astrobiology * Circumstellar habitable zone * Earth analog * Extraterrestrial liquid water * Habitability of natural satellites * Superhabitable planet Catalogues| * Catalog of Nearby Habitable Systems * Exoplanet Data Explorer * Extrasolar Planets Encyclopaedia * NASA Exoplanet Archive * NASA Star and Exoplanet Database Lists| * Exoplanetary systems * Host stars * Multiplanetary systems * Stars with proplyds * Exoplanets * Lists of exoplanets * Discoveries * Extremes * Firsts * Nearest * Largest * Most massive * Terrestrial candidates * Kepler * Potentially habitable * Discovered exoplanets by year * before 2000 * 2000–2009 * 2010 * 2011 * 2012 * 2013 * 2014 * 2015 * 2016 * 2017 * 2018 * 2019 Other| * Carl Sagan Institute * Exoplanet phase curves * Nexus for Exoplanet System Science * Planets in science fiction * Sudarsky's gas giant classification * Discoveries of exoplanets * Search projects * v * t * e 2019 in space * « 2018 2020 » Space probe launches | * Beresheet (lunar lander; Feb 2019) * Chandrayaan-2 / Vikram / Pragyan (lunar obiter, lander and rover; Jul 2019) Impact events| * Kamchatka meteor (announced) * 2019 MO Selected NEOs| * Asteroid close approaches * 2016 AZ8 * 2018 XB4 * (12538) 1998 OH * 66391 Moshup * 1620 Geographos * 2100 Ra-Shalom * 2006 QV89 * 2019 SU3 * 2019 TA7 * 2019 UN13 Exoplanets | * K2-288Bb * Wolf 359 b and c * Struve 2398 Bb and Bc * Luyten's Star d and e * L 1159-16 b, c, and d * Gliese 687 c * AD Leonis b * Gliese 251 c * LP 816-60 b * Gliese 754 b * Gliese 588 b and c * Gliese 784 b * Gliese 555 b * Teegarden's Star b and c Discoveries| * 2019 AQ3 * ASASSN-19bt * EPIC 204376071 * FarFarOut * K2-18b water vapor detected on exoplanet * Messier 87 supermassive black hole M87* imaged * 2I/Borisov * WD 0145+234 detection of exoasteroid disruption * WD J0914+1914 Comets | * 289P/Blanpain * 78P/Gehrels * 168P/Hergenrother * 163P/NEAT * 138P/Shoemaker–Levy * 171P/Spahr Space exploration| * New Horizons (encounter with 486958 Arrokoth; Dec 2018 / Jan 2019) * Chang'e 4 / Yutu-2 (landing on the far side of the Moon; Jan 2019) * Hayabusa2 (departure from 162173 Ryugu; Dec 2019) * Category:2018 in space — Category:2019 in space — Category:2020 in space 0.00 (0 votes) Original source: https://en.wikipedia.org/wiki/K2-288Bb. 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