K2-155d is a potentially habitable

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 ...

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 ...

in the K2-155 system. It is the outermost of three known planets orbiting around the K-type star K2-155 in the constellation

Taurus Taurus is Latin for 'bull' and may refer to: * Taurus (astrology), the astrological sign ** Vṛṣabha, in vedic astrology * Taurus (constellation), one of the constellations of the zodiac * Taurus (mythology), one of two Greek mythological ch ...

, approximately 290

light year A light-year, alternatively spelled light year (ly or lyr), is a unit of length used to express astronomical distance, astronomical distances and is equal to exactly , which is approximately 9.46 trillion km or 5.88 trillion mi. As defined by t ...

s (90

parsec The parsec (symbol: pc) is a unit of length used to measure the large distances to astronomical objects outside the Solar System, approximately equal to or (AU), i.e. . The parsec unit is obtained by the use of parallax and trigonometry, and ...

s) from Earth. It is one of 15 new exoplanets around red dwarf stars discovered by Japanese astronomer Teruyuki Hirano of the

Tokyo Institute of Technology The Tokyo Institute of Technology () was a public university in Meguro, Tokyo, Japan. It merged with Tokyo Medical and Dental University to form the Institute of Science Tokyo on 1 October 2024. The Tokyo Institute of Technology was a De ...

and his team. The team used data from NASA's

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 ...

during its extended K2 "Second Light" mission. K2-155d orbits near the so-called habitable zone of its system, and has the potential to host liquid water.

Discovery and observations

K2-155d is one of 15 exoplanets discovered by a team of Japanese astronomers led by Teruyuki Hirano at the Tokyo Institute of Technology. Its discovery is based on data from the K2 mission of NASA's Kepler spacecraft. The exoplanet has also been observed from ground-based telescopes including the

Nordic Optical Telescope The Nordic Optical Telescope (NOT) is an astronomical telescope located at Roque de los Muchachos Observatory, La Palma in the Canary Islands. The telescope saw first light in 1988, and was officially inaugurated during September 1989. Regular o ...

(NOT) in La Palma and the

Subaru Telescope is the telescope of the National Astronomical Observatory of Japan, located at the Mauna Kea Observatory on Hawaii. It is named after the open star cluster known in English as the Pleiades. It had the largest monolithic primary mirror in the ...

in Hawaii. Its characteristics were confirmed using

speckle imaging Speckle imaging comprises a range of high-resolution astronomical imaging techniques based on the analysis of large numbers of short exposures that freeze the variation of atmospheric turbulence. They can be divided into the shift-and-add ("' ...

and high-dispersion optical spectroscopy. The mass of K2-155d and the brightness of its host star may be measured by future observations from the

W. M. Keck Observatory The W. M. Keck Observatory is an astronomical observatory with two telescopes at an elevation of 4,145 meters (13,600 ft) near the summit of Mauna Kea in the U.S. state of Hawaii. Both telescopes have aperture primary mirrors, and, when c ...

and the

James Webb Space Telescope The James Webb Space Telescope (JWST) is a space telescope designed to conduct infrared astronomy. As the largest telescope in space, it is equipped with high-resolution and high-sensitivity instruments, allowing it to view objects too old, Lis ...

. The brightness of its host star makes K2-155d a good target for future studies using instruments such as the James Webb Space Telescope.

Characteristics

K2-155d is a super-Earth exoplanet with a radius 1.64 times that of Earth, near the transition zone between small rock-based and larger gaseous planets. Climate models predict that it is located near its star's

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 ...

and has an

insolation Solar irradiance is the power per unit area ( surface power density) received from the Sun in the form of electromagnetic radiation in the wavelength range of the measuring instrument. Solar irradiance is measured in watts per square metre ...

1.67 ± 0.38 (between 1.29 and 2.05) times that of Earth. Its physical temperature is estimated to be 289 K (16 degrees Celsius or 61 degrees Fahrenheit). Studies have shown that the planet would maintain a moderate surface temperature if its insolation is smaller than ~1.5 times that of Earth. K2-155d is one of three known planets in the system orbiting K2-155, a red dwarf star located from Earth. Its parent star has 88% less volume than the Sun. K2-155d orbits its star with a 40.7 day period, but as the planet is tidally locked the same side always faces its sun. K2-155d has an orbital radius of 0.1886AU and studies suggest that the planet has a low orbital eccentricity.

Potential habitability

K2-155d has been labeled a potentially habitable planet that may be able to harbor liquid water. A three-dimensional

climate simulation Numerical climate models (or climate system models) are mathematical models that can simulate the interactions of important drivers of climate. These drivers are the atmosphere, oceans, land surface and ice. Scientists use climate models to stu ...

was used to confirm the possibility of the existence of water. However, its discoverer Teruyuki Hirano was cautious about the findings, stating that they do not guarantee K2-155d is habitable, as the ranges in its orbit and temperature allow the possibility of it being outside the habitable zone. Factors such as the absence of solar flares could also decide if K2-155d is habitable. K2-155d

References

{{Taurus (constellation) Exoplanets discovered in 2018 Super-Earths in the habitable zone Taurus (constellation) Transiting exoplanets Discoveries by the Mauna Kea Observatories

155 Year 155 ( CLV) was a common year starting on Tuesday of the Julian calendar. At the time, it was known as the Year of the Consulship of Severus and Rufinus (or, less frequently, year 908 ''Ab urbe condita''). The denomination 155 for this year ...