The post-transit tail of WASP-107b observed at 10830A

TL;DR

This study observed the exoplanet WASP-107b at 10830 A, revealing a significant post-transit tail extending to twice the Roche radius, providing insights into atmospheric escape processes influenced by stellar winds.

Contribution

First-time detection of a post-transit tail at 10830 A for WASP-107b, with extended phase coverage and the largest absorption signal observed, advancing understanding of atmospheric escape.

Findings

Detected excess absorption after transit indicating a comet-like tail

Tail extends up to ~7 planetary radii, twice the Roche lobe

WASP-107b shows the most extended tail at 10830 A to date

Abstract

Understanding the effects of high-energy radiation and stellar winds on planetary atmospheres is vital for explaining the observed properties of close-in exoplanets. Observations of transiting exoplanets in the triplet of metastable helium lines at 10830 A allow extended atmospheres and escape processes to be studied for individual planets. We observed one transit of WASP-107b with NIRSPEC on Keck at 10830 A. Our observations, for the first time, had significant post-transit phase coverage, and we detected excess absorption for over an hour after fourth contact. The data can be explained by a comet-like tail extending out to ~7 planet radii, which corresponds to roughly twice the Roche lobe radius of the planet. Planetary tails are expected based on 3D simulations of escaping exoplanet atmospheres, particularly those including the interaction between the escaped material and strong stellar winds, and have been previously observed at 10830 A, in at least one other exoplanet. With both the largest mid-transit absorption signal and the most extended tail observed at 10830 A, WASP-107b remains a keystone exoplanet for atmospheric escape studies.