Astronomers have discovered a frozen exoplanet nearly the size of Neptune orbiting the quiet G9-type dwarf star K2-263.
An artist’s impression of the Neptune-sized exoplanet K2-263b. Image credit: Sci-News.com.
The newfound alien world, named K2-263b, has a radius of 2.41 Earth radii.
The planet takes only 50.8 days to circle its parent star, K2-263.
Also known as EPIC 211682544, the star is slightly less massive and smaller than the Sun (0.88 solar masses and 0.85 solar radii).
It is located at a distance of 532 light-years from Earth and has an apparent magnitude of 11.6.
K2-263b was originally spotted in data from NASA’s Kepler/K2 mission.
University of St Andrews astronomer Annelies Mortier and co-authors then used the HARPS-N high precision spectrometer on the Telescopio Nazionale Galileo in La Palma, Spain, to measure the periodic velocity of the planet and thus to derive its mass.
From the orbital details the astronomers obtained an exoplanet mass of 14.8 Earth-masses and a hence a density of about 5.6 g/cm3 (for comparison, the density of water is 1 g/cm3, and the average density of the rocky Earth is 5.51 g/cm3).
K2-263b most likely contains an equivalent amount of ices compared to rocks, roughly consistent with current ideas about planet formation and the relative abundances in a circumstellar nebula of the building-block elements like iron, nickel, magnesium, silicon, oxygen, carbon and nitrogen.
“Its mass of 14.8 Earth masses together with its estimated composition (half rock+metal and half ices) suggest that K2-263b likely formed in a similar way as the cores of giant planets in our own Solar System (Jupiter, Saturn, Uranus, Neptune), but for some reason, it did not accrete much gas,” Dr. Mortier and colleagues said.
The discovery is described in a paper in the December 2018 issue of the Monthly Notices of the Royal Astronomical Society (arXiv.org preprint).
_____
Andrew W. Mayo et al. 2018. 275 Candidates and 149 Validated Planets Orbiting Bright Stars in K2 Campaigns 0-10. AJ 155, 136; doi: 10.3847/1538-3881/aaadff
A. Mortier et al. 2018. K2-263b: a 50 d period sub-Neptune with a mass measurement using HARPS-N. MNRAS 481 (2): 1839-1847; doi: 10.1093/mnras/sty2360
