K2-155d is a potentially habitable Super-Earth exoplanet in the K2-155 system.^[3] It is the outermost of three known planets orbiting around the K-type star K2-155 in the constellation Taurus.^[4] It is one of 15 new exoplanets around red dwarf stars discovered by Japanese astronomer "Teruyuki Hirano" of the Tokyo Institute of Technology and his team.^[5] The team used data from NASA's Kepler Space Telescope 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.^[6][3]

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.^[3] Its discovery is based on data from the K2 mission of NASA's Kepler spacecraft.^[3] 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.^[3] Its characteristics were confirmed using speckle imaging and high-dispersion optical spectroscopy.^[1] The mass of K2-155d and the brightness of its host star may be measured by future observations from the W. M. Keck Observatory and the James Webb Space Telescope.^[1] The brightness of its host star makes K2-155d a good target for future studies using instruments such as the James Webb Space Telescope.^[1]

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.^[7][1][6] Climate models predict that it is located near its star's habitable zone and has an insolation 1.67 ± 0.38 (between 1.29 and 2.05) times that of Earth.^[1] Its physical temperature is estimated to be 289 K (16 degrees Celsius or 61 degrees Fahrenheit).^[2] Studies have shown that the planet would maintain a moderate surface temperature if its insolation is smaller than ~1.5 times that of Earth.^[1]

K2-155d is one of three known planets in the system orbiting K2-155, a red dwarf star located 200 light years from Earth.^{[citation needed]} Its parent star has 88% less volume than the Sun.^[8] 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.^[3] K2-155d has an orbital radius of 0.1886 AU^[7] and studies suggest that the planet has a low orbital eccentricity.^[9]

Potential habitability

K2-155d has been labeled a potentially habitable planet that may be able to harbor liquid water.^[6][3] A three-dimensional climate simulation was used to confirm the possibility of the existence of water.^[3] 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.^[6] Factors such as the absence of solar flares could also decide if K2-155d is habitable.^[3]