New research has confirmed the presence of 15 exoplanets orbiting smaller, cooler red dwarf stars. These include three so-called "super-Earths," one of which is believed to have a key ingredient for life – liquid water.
In two studies recently published in the Astronomical Journal, researchers detailed their observations on data from the Kepler space telescope's K2 mission, which were combined with findings made using ground-based telescopes, such as Spain's Nordic Optical Telescope and Hawaii's Subaru Telescope. This allowed them to confirm the 15 new exoplanets and their host stars, including K2-155, which is located around 200 light-years from Earth. Three super-Earths were found to be orbiting that bright red dwarf, but it was the outermost planet, K2-155d, that stood out as possibly being within K2-155's habitable zone.
As noted by Phys.org, climate modeling simulations suggested that there is a chance that K2-155d, which has a radius about 1.6 times greater than our planet's, might have liquid water on its surface. But while the researchers' simulations further hinted at the exoplanet having an "Earth-like" atmosphere and other features, the study's lead author, Teruyuki Hirano of the Tokyo Institute of Technology, stressed that it isn't 100 percent certain that K2-155d is indeed a habitable super-Earth with at least some of the necessary ingredients for life.
With this important disclaimer in mind, the researchers added that more information needs to be gathered to truly confirm whether or not the super-Earth called K2-155d could support life. This includes more specific estimates of host star K2-155's radius and temperature, which can only be determined through follow-up research, which, according to Phys.org, may require the use of interferometric techniques. But the two new studies still yielded substantial takeaways, including the observation that planets orbiting red dwarfs might be similar to those that orbit stars with similar characteristics to the sun, though they may be smaller in number than those that orbit "solar-type stars."
"Red dwarf systems, especially coolest red dwarfs, are just beginning to be investigated, so they are very exciting targets for future exoplanet research," said Hirano.Hirano further commented on the finding that planets that orbit red dwarfs have a similar radius gap to planets orbiting solar-type stars, saying that his team's discovery was "unique," and that astronomers are currently trying to figure out the reason behind the radius gap. Furthermore, he speculated that photoevaporation, a phenomenon where electromagnetic radiation strips away a planet's atmosphere, might be the reason why there aren't too many large planets close to their host stars, and that the metallic content of a host star could be linked to the size of the planets that orbit it.
"Large planets are only discovered around metal-rich stars. 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."Going forward, Hirano is optimistic that NASA's Transiting Exoplanet Survey Satellite (TESS) would yield more information on potentially habitable super-Earths such as K2-155d. According to NASA's overview page for the satellite, TESS will observe more than 200,000 stars for their transits, or instances when a planet passes right in front of its host. The space agency also hopes to document over 1,500 transiting exoplanet candidates with TESS, including about 500 which could be classified as Earth-sized or super-Earth planets.