A new planet near the habitable zone around a bright cool star has been found.
The scientists have confirmed the existence of 15 new planets – including one ‘super-Earth’ that could harbour liquid water – orbiting small, cool stars near our solar system.
These stars, known as red dwarfs, are of enormous interest for studies of planetary formation and evolution, the study states.
A research team led by Teruyuki Hirano of Tokyo Institute of Technology’s Department of Earth and Planetary Sciences has validated 15 exoplanets orbiting red dwarf systems.
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.
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.
The findings are based on 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.
The researchers found that K2-155d could potentially have liquid water on its surface based on three-dimensional global climate simulations.
Hirano expressed both excitement and restraint, as he said, “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.”
A more precise estimate of the radius and temperature of the K2-155 star would be needed to conclude definitively whether K2-155d is habitable. Achieving such precision would require further studies, for example, using interferometric techniques.
A key outcome from the current studies was that planets orbiting red dwarfs may have remarkably similar characteristics to planets orbiting solar-type stars.
“It’s important to note that the number of planets around red dwarfs is much smaller than the number around solar-type stars,” said Hirano. “Red dwarf systems, especially coolest red dwarfs, are just beginning to be investigated, so they are very exciting targets for future exoplanet research.”
For example, while the so-called radius gap of planets around solar-type stars has been reported previously, this is the first time that researchers have shown a similar gap in planets around red dwarfs. “This is a unique finding, and many theoretical astronomers are now investigating what causes this gap,” said Hirano.
He added that the most likely explanation for the lack of large planets in the proximity of host stars is photoevaporation, which can strip away the envelope of the planetary atmosphere.