K2-155d
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K2-155d is a potentially habitable
Super-Earth A super-Earth is an extrasolar planet 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 ...
exoplanet 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 * Taurus (constellation), one of the constellations of the zodiac * Taurus (mythology), one of two Greek mythological characters named Taurus * '' Bos tauru ...
. It is one of 15 new exoplanets around red dwarf stars discovered by Japanese astronomer "Teruyuki Hirano" of the
Tokyo Institute of Technology is a national research university located in Greater Tokyo Area, Japan. Tokyo Tech is the largest institution for higher education in Japan dedicated to science and technology, one of first five Designated National University and selected as ...
and his team. The team used data from NASA's
Kepler Space Telescope The Kepler space telescope is a disused space telescope launched by NASA in 2009 to discover Earth-sized Exoplanet, planets orbiting other stars. Named after astronomer Johannes Kepler, the spacecraft was launched into an Earth-trailing heliocen ...
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 (NOT) in La Palma and the Subaru Telescope in Hawaii. Its characteristics were confirmed using
speckle imaging Speckle imaging describes 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 comp ...
and the James Webb Space Telescope. 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 circumstellar habitable zone (CHZ), or simply the habitable zone, is the range of orbits around a star within which a planetary surface can support liquid water given sufficient atmospheric pressure.J. F. Kast ...
and has an insolation 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 200 light years 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 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.


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 (link will display the full calendar) 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'' ...