Evolvability of life and purple bacteria on other worlds

Determine whether life, specifically anoxygenic phototrophic purple bacteria including purple sulfur bacteria and purple non-sulfur bacteria, can evolve on planets beyond Earth under plausible exoplanetary conditions.

Background

The paper presents laboratory reflectance spectra for diverse purple bacteria and models how such biopigments would affect the reflectance spectra of Earth-like exoplanets under various surface and cloud conditions. The results aim to expand the set of potential surface biosignatures beyond the traditional vegetation red edge by highlighting signatures of bacteriochlorophylls and carotenoids that may be well-suited to cooler stars and anoxic or microaerobic environments.

Despite these advances in spectral characterization and modeling, the fundamental question remains whether life—and in particular purple anoxygenic phototrophs akin to those studied—can originate and evolve on exoplanets. The authors explicitly acknowledge this uncertainty in their conclusions.