Telling twins apart: Exo-Earths and Venuses with transit spectroscopy

TL;DR

This paper investigates how the James Webb Space Telescope could differentiate between Earth-like and Venus-like atmospheres on terrestrial exoplanets through transit spectroscopy, focusing on ozone detection and cloud effects.

Contribution

It analyzes the potential and limitations of JWST in distinguishing exo-Earths from exo-Venuses using spectral features, especially ozone, considering cloud interference.

Findings

Ozone detection could identify oxygen-rich atmospheres in nearby habitable-zone planets.

Cloudiness in Venus-like atmospheres complicates spectral interpretation.

Detecting key atmospheric features requires about 100 transits per target.

Abstract

The planned launch of the James Webb Space Telescope in 2018 will herald a new era of exoplanet spectroscopy. JWST will be the first telescope sensitive enough to potentially characterize terrestrial planets from their transmission spectra. In this work, we explore the possibility that terrestrial planets with Venus-type and Earth-type atmospheres could be distinguished from each other using spectra obtained by JWST. If we find a terrestrial planet close to the liquid water habitable zone of an M5 star within a distance of 10 parsecs, it would be possible to detect atmospheric ozone if present in large enough quantities, which would enable an oxygen-rich atmosphere to be identified. However, the cloudiness of a Venus-type atmosphere would inhibit our ability to draw firm conclusions about the atmospheric composition, making any result ambiguous. Observing small, temperate planets with JWST requires significant investment of resources, with single targets requiring of order 100 transits to achieve sufficient signal to noise. The possibility of detecting a crucial feature such as the ozone signature would need to be carefully weighed against the likelihood of clouds obscuring gas absorption in the spectrum.