An article published in “The Astronomical Journal” describes the confirmation of 44 exoplanets that are part of an original group of 72 candidates detected by NASA’s Kepler space telescope. A team of researchers led by John Livingston of the University of Tokyo, Japan, used data collected by ESA’s Gaia space probe and ground-based telescopes in the US to confirm the existence of 44 exoplanets in one go and discover some of their characteristics. 16 of them have a radius less than twice the Earth’s.
Over the past 9 years of mission with the latest extension of the K2 mission decided in 2016, the Kepler space telescope has so far led to the discovery of over 2,600 exoplanets. A lot of candidates are still awaiting to be verified: in some very special cases a new statistical technique allowed the verification of a lot candidates in one go, like the 715 announced in February 2014, but other observations are usually conducted or at least a search for data in the archives of other telescopes to verify a few exoplanets at a time. In this case, however, 44 exoplanets of various types were verified in one go.
During the K2 mission, the Kepler space telescope conducted a series of campaigns focusing the observations each time on a small area of the sky. Between July 6 and September 20, 2016 it conducted its Campaign 10 (C10) in which it observed thousands of stars in search of transits, traces of the passage of exoplanets in front of them. 72 traces were examined by John Livingston’s team using data from the observations of ground-based telescopes and the Gaia space probe, a very special space telescope because it has the task of creating maps of the sky with all the objects it can detect.
The amount of data obtained allowed to confirm the existence of 44 of the candidates examined. They’re exoplanets very close to their stars, closer than Mercury to the Sun. The image (courtesy John Livingston) shows a scheme of these exoplanets with a reproduction, albeit approximate, of their size, their orbits with Mercury’s as a comparison and with the temperatures estimated on their surface.
John Livingston mentioned the 4 exoplanets closest to their stars, whose year lasts less than an Earth’s day: K2-131 b, K2-156 b, K2-223 b and K2-229 b. They’re called ultra-short period planets and so far they were a rarity so it was surprising to find 4 of them in one go even in a large group.
There’s a particular interest in ultra-short period exoplanets because according to current models of planetary formation they can’t have formed so close to their stars. The most likely hypothesis is that they formed at a greater distance and then approached following migration mechanisms that are also under study. It’s possible that originally ultra-short period planets of the rocky type were mini-Neptunes whose atmosphere was swept away by their star when they approached. Discovering 4 more of them could help to better understand their origin and evolution.
John Livingston also stressed the fact that out of the 44 exoplanets confirmed 16 are small, with a radius less than twice the Earth’s. The smallest ones are at the limit of the minimum size of detectable exoplanets so the researchers can be satisfied. 18 of the verified exoplanets are in multiplanet systems.
This study already offered good results and the confirmed exoplanets can be the subject of follow-up observations. However, there are 27 more candidates that are likely to be real planets but require follow-up checks to confirm their existence therefore the research continues.
Meanwhile, the Kepler space telescope is reaching the end of its mission because it’s running out of the fuel that allows it to perform some indispensable maneuvers. This planet hunter was an extraordinary success and its successor, NASA’s TESS space telescope, is already in space and a new mission is starting with excellent prospects.