The blue sky of GJ3470b: the atmosphere of a low-mass planet unveiled by ground-based photometry

TL;DR

This study uses ground-based photometry across multiple wavelengths to reveal atmospheric scattering in GJ3470b, a low-mass exoplanet, demonstrating the potential of large telescopes for detailed atmospheric characterization.

Contribution

First simultaneous UV and optical/infrared photometry of GJ3470b showing wavelength-dependent radius variation, indicating atmospheric scattering and low molecular weight gases.

Findings

Detected significant radius change with wavelength, indicating scattering.

Confirmed the feasibility of Earth-sized planet detection around M dwarfs with large ground telescopes.

Provided updated planetary parameters and orbital ephemeris.

Abstract

GJ3470b is a rare example of a "hot Uranus" transiting exoplanet orbiting a nearby M1.5 dwarf. It is of crucial interest for atmospheric studies because it is one of the most inflated low-mass planets known, bridging the boundary between "super-Earths" and Neptunian planets. We present two new ground-based light curves of GJ3470b gathered by the LBC camera at the Large Binocular Telescope. Simultaneous photometry in the ultraviolet (lambda_c = 357.5 nm) and optical infrared (lambda_c = 963.5 nm) allowed us to detect a significant change of the effective radius of GJ3470b as a function of wavelength. This can be interpreted as a signature of scattering processes occurring in the planetary atmosphere, which should be cloud-free and with a low mean molecular weight. The unprecedented accuracy of our measurements demonstrates that the photometric detection of Earth-sized planets around M dwarfs is achievable using 8-10m size ground-based telescopes. We provide updated planetary parameters, and a greatly improved orbital ephemeris for any forthcoming study of this planet.