The Optical and Near-Infrared Transmission Spectrum of the Super-Earth GJ1214b: Further Evidence for a Metal-Rich Atmosphere

TL;DR

This study presents a comprehensive transmission spectrum of GJ1214b across optical to near-infrared wavelengths, providing evidence for a metal-rich atmosphere or high-altitude clouds, challenging previous spectral feature detections.

Contribution

The paper offers new ground-based measurements and re-analysis of existing data, confirming a featureless spectrum and constraining atmospheric composition of GJ1214b.

Findings

Transmission spectrum is featureless across observed wavelengths.

K-band data contradicts previous spectral feature detections.

Atmosphere likely contains at least 70% water or has high-altitude clouds.

Abstract

We present an investigation of the transmission spectrum of the 6.5 M_earth planet GJ1214b based on new ground-based observations of transits of the planet in the optical and near-infrared, and on previously published data. Observations with the VLT+FORS and Magellan+MMIRS using the technique of multi-object spectroscopy with wide slits yielded new measurements of the planet's transmission spectrum from 0.61 to 0.85 micron, and in the J, H, and K atmospheric windows. We also present a new measurement based on narrow-band photometry centered at 2.09 micron with the VLT+HAWKI. We combined these data with results from a re-analysis of previously published FORS data from 0.78 to 1.00 micron using an improved data reduction algorithm, and previously reported values based on Spitzer data at 3.6 and 4.5 micron. All of the data are consistent with a featureless transmission spectrum for the planet. Our K-band data are inconsistent with the detection of spectral features at these wavelengths reported by Croll and collaborators at the level of 4.1 sigma. The planet's atmosphere must either have at least 70% water by mass or optically thick high-altitude clouds or haze to be consistent with the data.