Vol. 603
In section 10. Planets and planetary systems

Spectral and atmospheric characterization of 51 Eridani b using VLT/SPHERE

by M. Samland, P. Mollière, M. Bonnefoy, et al. A&A 603, A57


51 Eridani b is a highly interesting planet discovered recently through direct imaging. It is young (20 Myr), nearby (30 pc), has a mass around ten times that of Jupiter, and an orbital distance of about 14 au. Most importantly, its angular separation makes it an excellent target for direct spectroscopic characterization. Samland et al. use SPHERE at the VLT to obtain a precise spectrum of the planet from 0.95 to 1.7 microns. The planet is outside of the color-color relations for brown dwarfs. Models indicate that it is cloudy and has a very high metallicity ([Fe/H]=1.0 +/- 0.1), significantly above that of its parent star. This latter implies that the atmosphere of 51 Eri b is as metal-rich as that of Saturn. Given the trend between increasing planetary mass and decreasing atmospheric metallicity in the solar system, this is a somewhat surprising result, but definitely a very significant one.