Theoretical Transit Spectra for GJ 1214b and Other "Super-Earths"

TL;DR

This paper develops a flexible method for calculating transit spectra of super-Earths, applies it to GJ 1214b, and supports a hydrogen-rich atmosphere with haze, while providing a library of spectra for future studies.

Contribution

It introduces a new calculation method for super-Earth transit spectra with arbitrary compositions and applies it to GJ 1214b, clarifying its atmospheric nature.

Findings

Supports a hydrogen-rich atmosphere with haze for GJ 1214b

Rules out certain hydrogen-rich and hydrogen-poor models

Provides a library of theoretical spectra for future research

Abstract

We present new calculations of transit spectra of super-Earths that allow for atmospheres with arbitrary proportions of common molecular species and haze. We test this method with generic spectra, reproducing the expected systematics and absorption features, then apply it to the nearby super-Earth GJ 1214b, which has produced conflicting observational data, leaving the questions of a hydrogen-rich versus hydrogen-poor atmosphere and the water content of the atmosphere ambiguous. We present representative transit spectra for a range of classes of atmosphere models for GJ 1214b. Our analysis supports a hydrogen-rich atmosphere with a cloud or haze layer, although a hydrogen-poor model with less than 10% water is not ruled out. Several classes of models are ruled out, however, including hydrogen-rich atmospheres with no haze, hydrogen-rich atmospheres with a haze of about 0.01-micron tholin particles, and hydrogen-poor atmospheres with major sources of absorption other than water. We propose an observational test to distinguish hydrogen-rich from hydrogen-poor atmospheres. Finally, we provide a library of theoretical transit spectra for super-Earths with a broad range of parameters to facilitate future comparison with anticipated data.