Detectability of Surface Biosignatures for Directly-Imaged Rocky Exoplanets

TL;DR

This study assesses the detectability of surface biosignatures on rocky exoplanets using a next-generation space telescope model, highlighting the potential for identifying signs of life within 15 parsecs under various conditions.

Contribution

It introduces a realistic simulation combining a space telescope noise model with planetary spectra to evaluate biosignature detection feasibility for the first time.

Findings

Biosignatures could be detected within 1,000 hours at 15 parsecs.

Tighter telescope inner angles improve detection distances.

Anoxygenic biosignatures are more detectable than nonphotosynthetic ones.

Abstract

Modeling the detection of life has never been more opportune. With next generation space telescopes, like the currently developing Habitable Worlds Observatory (HWO) concept, we will begin to characterize rocky exoplanets potentially similar to Earth. However, currently, few realistic planetary spectra containing surface biosignatures have been paired with direct imaging telescope instrument models. Therefore, we use a HWO instrument noise model to assess the detection of surface biosignatures affiliated with oxygenic, anoxygenic, and nonphotosynthetic extremophiles. We pair the HWO telescope model to a 1-D radiative transfer model to estimate the required exposure times necessary for detecting each biosignature on planets with global microbial coverage and varying atmospheric water vapor concentrations. For modeled planets with 0% - 50% cloud coverage, we determine pigments and the red edge could be detected within 1,000 hours (100 hours) at distances within 15 pc (11 pc). However, tighter telescope inner working angles (2.5 lambda/D) would allow surface biosignature detection at further distances. Anoxygenic photosynthetic biosignatures could also be more easily detectable than nonphotosynthetic pigments and the photosynthetic red edge when compared against a false positive iron oxide slope. Future life detection missions should evaluate the influence of false positives on the detection of multiple surface biosignatures.