K2-18, also known as EPIC 201912552, is a

red dwarf A red dwarf is the smallest kind of star on the main sequence. Red dwarfs are by far the most common type of fusing star in the Milky Way, at least in the neighborhood of the Sun. However, due to their low luminosity, individual red dwarfs are ...

star A star is a luminous spheroid of plasma (physics), plasma held together by Self-gravitation, self-gravity. The List of nearest stars and brown dwarfs, nearest star to Earth is the Sun. Many other stars are visible to the naked eye at night sk ...

with two planetary companions located from

Earth Earth is the third planet from the Sun and the only astronomical object known to Planetary habitability, harbor life. This is enabled by Earth being an ocean world, the only one in the Solar System sustaining liquid surface water. Almost all ...

, in the

constellation A constellation is an area on the celestial sphere in which a group of visible stars forms Asterism (astronomy), a perceived pattern or outline, typically representing an animal, mythological subject, or inanimate object. The first constellati ...

Leo Leo is the Latin word for lion. It most often refers to: * Leo (constellation), a constellation of stars in the night sky * Leo (astrology), an astrological sign of the zodiac * Leo (given name), a given name in several languages, usually mas ...

. Its name is because it was discovered by the K2 Mission, which extended the mission of the Kepler Space Telescope after failure of two of its reaction wheels.

Planetary system

The star has a transiting

exoplanet An exoplanet or extrasolar planet is a planet outside the Solar System. The first confirmed detection of an exoplanet was in 1992 around a pulsar, and the first detection around a main-sequence star was in 1995. A different planet, first det ...

, called

K2-18b K2-18b, also known as EPIC 201912552 b, is an exoplanet orbiting the red dwarf K2-18, located away from Earth. The planet is a sub-Neptune about 2.6 times the Earth radius, radius of Earth, with a 33-day orbit within the star's habitable zone; ...

, a

super-Earth A super-Earth is a type of exoplanet with a mass higher than Earth, but substantially below those of the Solar System's ice giants, Uranus and Neptune, which are 14.5 and 17.1 times Earth's, respectively. The term "super-Earth" refers only to t ...

located within the

habitable zone In astronomy and astrobiology, the habitable zone (HZ), or more precisely the circumstellar habitable zone (CHZ), is the range of orbits around a star within which a planetary surface can support liquid water given sufficient atmospheric pressu ...

of K2-18. It was discovered in 2015 by the

Kepler space telescope The Kepler space telescope is a defunct space telescope launched by NASA in 2009 to discover Earth-sized planets orbiting other stars. Named after astronomer Johannes Kepler, the spacecraft was launched into an Earth-trailing heliocentric orb ...

in its K2 mission. It is the first exoplanet in the habitable zone, albeit a hydrogen-rich

sub-Neptune The term sub-Neptune can refer to a planet with a smaller radius than Neptune even though it may have a larger mass or to a planet with a smaller mass than Neptune even though it may have a larger radius like a super-puff and both meanings can ev ...

,No, the Exoplanet K2-18b Is Not Habitable
/ref> to have its atmosphere characterized; initially thought to contain

water vapor Water vapor, water vapour, or aqueous vapor is the gaseous phase of Properties of water, water. It is one Phase (matter), state of water within the hydrosphere. Water vapor can be produced from the evaporation or boiling of liquid water or from th ...

, more recent observations have instead detected

methane Methane ( , ) is a chemical compound with the chemical formula (one carbon atom bonded to four hydrogen atoms). It is a group-14 hydride, the simplest alkane, and the main constituent of natural gas. The abundance of methane on Earth makes ...

and

carbon dioxide Carbon dioxide is a chemical compound with the chemical formula . It is made up of molecules that each have one carbon atom covalent bond, covalently double bonded to two oxygen atoms. It is found in a gas state at room temperature and at norma ...

. The presence of these molecules and non-detection of

ammonia Ammonia is an inorganic chemical compound of nitrogen and hydrogen with the chemical formula, formula . A Binary compounds of hydrogen, stable binary hydride and the simplest pnictogen hydride, ammonia is a colourless gas with a distinctive pu ...

is consistent with predictions for a

hycean planet A hycean planet ( ) is a Hypothetical astronomical object, hypothetical type of planet with liquid water oceans underneath a hydrogen-rich atmosphere. Definition The term ''hycean'' is a Blend word, portmanteau of ''hydrogen'' and ''ocean'' ...

. A second, non-transiting planet, K2-18c, was discovered in 2017 by

radial velocity The radial velocity or line-of-sight velocity of a target with respect to an observer is the rate of change of the vector displacement between the two points. It is formulated as the vector projection of the target-observer relative velocity ...

with

HARPS The High Accuracy Radial Velocity Planet Searcher (HARPS) is a high-precision Echelle grating, echelle planet-finding spectrograph installed in 2002 on the ESO 3.6 m Telescope, ESO's 3.6m telescope at La Silla Observatory in Chile. The First l ...

. This planet was challenged by another team with CARMENES data, but its existence was reaffirmed by the discovery team based on both HARPS and CARMENES data. This planet has also been confirmed by a later independent study. System tidal simulation suggests that K2-18c is a gas-rich, Neptune-like planet, similar to K2-18b.

References

External links

NASA says distant planet could hold life after they spot signs of rare water ocean - MSN News
{{DEFAULTSORT:K2-18 Leo (constellation) M-type main-sequence stars Planetary systems with two confirmed planets J11301450+0735180