The existence of 15 new planets including one ‘super-Earth’ that could harbor liquid water, is reported by a team of astronomers in Japan. The planets orbit small cool stars – known as red dwarfs – located near our solar system.
One of the brightest red dwarfs, K2-155 that is around 200 light years away from Earth, has three transiting super-Earths, which are slightly bigger than our own planet.
Conceptual illustration. A key outcome from the current studies was that planets orbiting red dwarfs may have remarkably similar characteristics to planets orbiting solar-type stars. Credit: Tokyo Institute of Technology
Of those three super-Earths, the outermost planet, K2-155d, with a radius 1.6 times that of Earth, could be within the host star’s habitable zone.
“In our simulations, the atmosphere and the composition of the planet were assumed to be Earth-like, and there’s no guarantee that this is the case,” Teruyuki Hirano of Tokyo Institute of Technology’s Department of Earth and Planetary Sciences, who led the team in this study, said in a press release.
K2-155d could potentially have liquid water on its surface based on three-dimensional global climate simulations. However, further and more precise estimate of the radius and temperature of the K2-155 star would be needed to conclude if K2-155d is indeed habitable.
“It’s important to note that the number of planets around red dwarfs is much smaller than the number around solar-type stars,” says Hirano. “Red dwarf systems, especially coolest red dwarfs, are just beginning to be investigated, so they are very exciting targets for future exoplanet research.”
The researchers also investigated the relationship between planet radius and metallicity of the host star.
“Large planets are only discovered around metal-rich stars,” Hirano says, “and what we found was consistent with our predictions. The few planets with a radius about three times that of Earth were found orbiting the most metal-rich red dwarfs.”
In April 2018, NASA will launch Transiting Exoplanet Survey Satellite (TESS) and hopefully more planets will be discovered.
“TESS is expected to find many candidate planets around bright stars closer to Earth,” Hirano says. “This will greatly facilitate follow-up observations, including investigation of planetary atmospheres and determining the precise orbit of the planets.”
Researchers used data from NASA Kepler spacecraft’s second mission, K2, and follow-up observations using ground-based telescopes, including the Subaru Telescope in Hawaii and the Nordic Optical Telescope (NOT) in Spain.