K2-155d

Lore & Background

K2-155d was discovered by a team of Japanese astronomers led by Teruyuki Hirano at the Tokyo Institute of Technology, based on data from NASA's Kepler space telescope during its K2 'Second Light' mission. The discovery was part of a group of 15 new exoplanets around red dwarf stars. Observations from ground-based telescopes, including the Nordic Optical Telescope in La Palma and the Subaru Telescope in Hawaii, helped confirm the planet's characteristics using speckle imaging and high-dispersion optical spectroscopy. Future observations from the W. M. Keck Observatory and the James Webb Space Telescope may measure the planet's mass and the brightness of its host star.

The planet is a super-Earth with a radius 1.64 times that of Earth, placing it near the transition zone between small rocky planets and larger gaseous planets. It orbits its star every 40.7 days at a distance of 0.1886 AU, and studies suggest a low orbital eccentricity. The planet is tidally locked, meaning the same side always faces its star. Climate models indicate it is located near the habitable zone, with an insolation of 1.67 ± 0.38 times that of Earth and an estimated physical temperature of 289 K. Studies have shown that the planet would maintain a moderate surface temperature if its insolation is smaller than about 1.5 times that of Earth.

K2-155d has been labeled a potentially habitable planet that may be able to harbor liquid water, based on a three-dimensional climate simulation. However, its discoverer Teruyuki Hirano cautioned that the findings do not guarantee habitability, 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 determine whether the planet is habitable.

Reader's Guide

K2-155d is significant as a potentially habitable super-Earth located near the habitable zone of its K-type star, making it a candidate for future studies of exoplanet atmospheres and habitability. Its discovery as part of a group of 15 exoplanets around red dwarf stars highlights the productivity of the K2 mission in finding small planets around low-mass stars. The planet's brightness of its host star makes it a good target for future observations with instruments such as the James Webb Space Telescope, which could provide further insights into its mass and atmospheric composition. The cautious assessment by its discoverer, Teruyuki Hirano, underscores the uncertainty in determining habitability, as the planet's orbit and temperature ranges allow for both habitable and non-habitable scenarios. The use of three-dimensional climate simulations to confirm the possibility of liquid water represents a methodological advance in exoplanet studies. K2-155d's legacy lies in its role as a benchmark for studying the transition between rocky and gaseous planets and for refining the criteria for potential habitability in exoplanetary systems.

Did You Know?

• The planet orbits its star every 40.7 days and is tidally locked, with the same side always facing its sun.
• Its radius is 1.64 times that of Earth, near the transition zone between small rocky and larger gaseous planets.
• A three-dimensional climate simulation was used to confirm the possibility of liquid water on the planet.