Vol. 633
Sect. 10. Planets and planetary systems

Peering into the formation history of beta Pictoris b with VLTI/GRAVITY long-baseline interferometry

by GRAVITY Collaboration 2020, A&A, 633, A110

The 4th-magnitude beta Pictoris hosts an emblematic young planetary system that includes both one of the first debris disks, detected 30 years ago, and one of the first directly detected giant exoplanets a decade ago. Nowak et al. use the GRAVITY instrument on the VLT Interferometer to obtain both a high-quality R=500 K-band spectrum of the Beta Pic b planet and its position relative to the star with 50 microarcsecond accuracy. Together with archival astrometry, the new star-planet position indicates that their orbit is mildly eccentric and it improves previous mass measurements of the planet to 12.7 +- 2.2 Mjup mass. The authors also analyze the spectrum to derive a subsolar C/O abundance ratio in the planetary atmosphere, which points towards a formation of the planet through core accretion somewhere between the CO2 and H2O ice lines. Coupled with previous observations of the HR 8799 system, these observations demonstrate the great potential of spectrally resolved long baseline interferometry to characterize young planets and their formation mechanisms.