Exoplanet GJ3470b is a Hot Neptune With Clear, Blue Skies

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

Authors:

V. Nascimbeni, G. Piotto, I. Pagano, G. Scandariato, E. Sani, and M. Fumana

Abstract:

GJ3470b is a rare example of a “hot Uranus” transiting exoplanet orbiting a nearby M1.5 dwarf. It is crucial 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 ( c = 357.5 nm) and optical infrared ( c = 963.5 nm) allowed us to detect a significant change in 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.