Exoplanet atmospheres

Abstract:

The James Webb Space Telescope (JWST) may be capable of finding biogenic gases in the atmospheres of habitable exoplanets around low-mass stars. Considerable attention has been given to the detectability of biogenic oxygen, which could be found using an ozone proxy, but ozone detection with JWST will be extremely challenging, even for the most favorable targets. Here, we investigate the detectability of biosignatures in anoxic atmospheres analogous to those that likely existed on the early Earth. Arguably, such anoxic biosignatures could be more prevalent than oxygen biosignatures if life exists elsewhere. Specifically, we simulate JWST retrievals of TRAPPIST-1e to determine whether the methane plus carbon dioxide disequilibrium biosignature pair is detectable in transit transmission. We find that ~10 transits using the Near InfraRed Spectrograph prism instrument may be sufficient to detect carbon dioxide and constrain methane abundances sufficiently well to rule out known, nonbiological CH4 production scenarios to ~90% confidence. Furthermore, it might be possible to put an upper limit on carbon monoxide abundances that would help rule out nonbiological methane-production scenarios, assuming the surface biosphere would efficiently draw down atmospheric CO. Our results are relatively insensitive to high-altitude clouds and instrument noise floor assumptions, although stellar heterogeneity and variability may present challenges.

Abstract:

We present observations of WASP-63b by the Hubble Space Telescope (HST) as part of "A Preparatory Program to Identify the Single Best Transiting Exoplanet for James Webb Space Telescope (JWST) Early Release Science (ERS)." WASP-63b is one of the community targets under consideration for the JWST ERS program. We present a spectrum derived from a single observation by HST Wide Field Camera 3 in the near-infrared. We engaged groups across the transiting exoplanet community to participate in the analysis of the data and present results from each. Extraction of the transmission spectrum by several independent analyses find an H2O absorption feature with varying degrees of significance ranging from 1σ to 3σ. The feature, in all cases, is muted in comparison to a clear atmosphere at solar composition. The reasons for the muting of this feature are ambiguous due to a degeneracy between clouds and composition. The data does not yield robust detections of any molecular species other than H2O. The group was motivated to perform an additional set of retrieval exercises to investigate an apparent bump in the spectrum at ~1.55 μm. We explore possible disequilibrium chemistry and find this feature is consistent with super-solar HCN abundance but it is questionable if the required mixing ratio of HCN is chemically and physically plausible. The ultimate goal of this study is to vet WASP-63b as a potential community target to best demonstrate the capabilities and systematics of JWST instruments for transiting exoplanet science. In the case of WASP-63b, the presence of a detectable water feature indicates that WASP-63b remains a plausible target for JWST observations.

Abstract:

Both the global average per capita consumption of meat and the total amount of meat consumed are rising, driven by increasing average individual incomes and by population growth. The consumption of different types of meat and meat products has substantial effects on people’s health, and livestock production can have major negative effects on the environment. Here, we explore the evidence base for these assertions and the options policy-makers have should they wish to intervene to affect population meat consumption. We highlight where more research is required and the great importance of integrating insights from the natural and social sciences.