Astronomers using data from NASA’s Kepler K2 mission have discovered two new planetary systems, one of which contains two super-Earths and the other has three Earth-size exoplanets.
An artist’s concept of the K2-239 planetary system. Image credit: Gabriel Perez Diaz, SMM / IAC.
The first planetary system was found around K2-239, also knows as EPIC 248545986, a spectral type M3V star located 160 light-years away in the constellation Sextans.
The star has a radius about 36% that of our Sun, a mass 40% that of the Sun, and is home to at least three Earth-size transiting planets.
Named K2-239b, c and d, the planets in this system have estimated radii of 1.1, 1 and 1.1 Earth radii.
They have orbital periods of 5.2, 7.8, and 10 days, and are located at distances of 0.04, 0.06 and 0.07 AU (astronomical units), respectively.
The second system was found in around K2-240 (EPIC 249801827), an M0.5V star located 228 light-years from Earth.
The star has a radius about 54% that of our Sun, a mass 58% that of the Sun, and hosts two transiting super-Earths with radii about 2.0 and 1.8 Earth radii.
Dubbed K2-240b and c, the planets make a circle around their parent star once every 6.03 and 20.5 days at distances of 0.05 and 0.12 AU, respectively.
As their names suggest, the five newfound planets were discovered by the NASA Kepler spacecraft’s reborn K2 mission.
“The equilibrium temperatures of the atmospheres of these planets are estimated to be in the range of 225-621 degrees Fahrenheit (107-327 degrees Celsius),” said team leader Francisco Javier De Cos Juez, an astronomer at the University of Oviedo, and colleagues.
“This makes them suitable targets for incoming exoplanet-exploring facilities:
(i) ESA’s PLAnetary Transits and Oscillations of stars (PLATO) could reveal transit timing variations that allow accurate planetary masses to be estimated;
(ii) the NASA/ESA/CSA James Webb Space Telescope (JWST) could find signs of planetary atmospheres;
(iii) ultra-stable spectrographs such as ESPRESSO at ESO’s Very Large Telescope, could also carry out radial velocity follow-up, so these are promising targets to improve our understanding of compact Earth-sized planetary systems (K2-239) and super-Earth systems on the rocky-gaseous boundary (K2-240).”
A paper reporting this discovery is published in the Monthly Notices of Royal Astronomical Society (arXiv.org preprint).
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E. Díez Alonso et al. Two planetary systems with transiting Earth-size and super-Earth planets orbiting late-type dwarf stars. MNRAS, published online June 6, 2018; doi: 10.1093/mnrasl/sly102
