The HARPS search for southern extra-solar planets. XXVIII (C. Lovis et al.)

Vol. 528
In section 10. Planets and planetary systems

The HARPS search for southern extra-solar planets. XXVIII. Up to seven planets orbiting HD 10180: probing the architecture of low-mass planetary systems

Exoplanets of the size of Jupiter tend not to like the company of other peers. In contrast, small exoplanets in the super-Earth to Neptune-mass range tend to come in groups. A striking example announced by Lovis et al. is HD 10180, a system that contains up to seven planets between 0.06 and 0.14 AU, with masses ranging from 1.4 to 65 Earth masses. The planetary system was discovered with the HARPS spectrograph. The signal is so complex that it took 6 years and 190 radial velocity points to be able to start disentangling the contributions of the different planets! The discovery of such a rich, nonresonant system is a challenge to formation theories.