Non-Detection of a Helium Exosphere for the Hot Jupiter WASP-12b

TL;DR

This study reanalyzed archival data of exoplanet WASP-12b to search for helium exosphere signatures, finding no significant detection, which aligns with theoretical predictions and highlights the importance of stellar and geometric factors.

Contribution

It provides the first non-detection of helium exosphere around WASP-12b and discusses factors affecting helium signal strength, informing future observational strategies.

Findings

No significant helium absorption detected in WASP-12b data

Theoretical models predict a weak helium signal consistent with observations

Helium signal strength is highly sensitive to stellar spectrum and gas geometry

Abstract

An exosphere was recently detected around the exoplanet WASP-107b, a low-density, warm Neptune, based on an absorption feature from metastable helium (which has a vacuum wavelength of 10833 \AA). Inspired by the WASP-107b detection, we reanalyzed archival HST observations of another evaporating exoplanet, WASP-12b, to search for signs of helium in its exosphere. We find no significant increase in transit depth at 10833 \AA. We compare this result to theoretical predictions from a 1D model, and find that the expected helium feature amplitude is small, in agreement with the observed non-detection. We discuss possible explanations for why the helium feature is weaker for WASP-12b than WASP-107b, and conclude that the amplitude of the signal is highly sensitive to the stellar spectrum and the geometry of the evaporating gas cloud. These considerations should be taken into account in the design of future searches for helium exospheres.