The Dark World: A Tale of WASP-43b in Reflected Light with HST WFC3/UVIS

TL;DR

This study used HST WFC3/UVIS to observe reflected light from exoplanet WASP-43b, setting upper limits on its brightness and suggesting a very dark, cloud-free dayside atmosphere consistent with previous models.

Contribution

First optical reflected light eclipse measurement of WASP-43b with UVIS, including a novel scanning extraction pipeline and atmospheric constraints.

Findings

Eclipse depth upper limit of 67 ppm indicating a dark atmosphere

No detectable clouds within probed pressure levels (>1 bar)

Results align with previous GCM predictions and suggest cloud-free dayside

Abstract

Optical, reflected light eclipse observations provide a direct probe of the exoplanet scattering properties, such as from aerosols. We present here the photometric, reflected light observations of WASP-43b using the HST WFC3/UVIS instrument with the F350LP filter (346-822nm) encompassing the entire optical band. This is the first reflected light, photometric eclipse using UVIS in scanning mode; as such we further detail our scanning extraction and analysis pipeline Arctor. Our HST WFC3/UVIS eclipse light curve for WASP-43 b derived a 3-{\sigma} upper limit of 67 ppm on the eclipse depth, which implies that WASP-43b has a very dark dayside atmosphere. With our atmospheric modeling campaign, we compared our reflected light constraints with predictions from global circulation and cloud models, benchmarked with HST and Spitzer observations of WASP-43b. We infer that we do not detect clouds on the dayside within the pressure levels probed by HST WFC3/UVIS with the F350LP filter (P > 1 bar). This is consistent with the GCM predictions based on previous WASP-43b observations. Dayside emission spectroscopy results from WASP-43b with HST and Spitzer observations are likely to not be significantly affected by contributions from cloud particles.