Rayleigh Scattering in the Atmosphere of the Warm Exo-Neptune GJ 3470b

TL;DR

This study confirms Rayleigh scattering in the atmosphere of GJ 3470b, a small exoplanet, using ground-based observations, indicating a hydrogen/helium atmosphere with clouds and hazes.

Contribution

First ground-based confirmation of Rayleigh scattering in GJ 3470b's atmosphere, demonstrating atmospheric characterization feasibility with small telescopes.

Findings

Confirmed strong Rayleigh scattering slope in GJ 3470b

Detected a hydrogen/helium-dominated atmosphere with clouds and hazes

Established ground-based observations as effective for exoplanet atmospheric studies

Abstract

GJ 3470b is a warm Neptune-size planet transiting a M dwarf star. Like the handful of other small exoplanets for which transmission spectroscopy has been obtained, GJ 3470b exhibits a flat spectrum in the near- and mid-infrared. Recently, a tentative detection of Rayleigh scattering in its atmosphere has been reported. This signal manifests itself as an observed increase of the planetary radius as a function of decreasing wavelength in the visible. We set out to verify this detection and observed several transits of this planet with the LCOGT network and the Kuiper telescope in four different bands (Sloan g', Sloan i', Harris B and Harris V). Our analysis reveals a strong Rayleigh scattering slope, thus confirming previous results. This makes GJ 3470b the smallest known exoplanet with a detection of Rayleigh scattering. We find that the most plausible scenario is a hydrogen/helium-dominated atmosphere covered by clouds which obscure absorption features in the infrared and hazes which give rise to scattering in the visible. Our results demonstrate the feasibility of exoplanet atmospheric characterization from the ground, even with meter-class telescopes.