Colors of extreme exo-Earth environments

TL;DR

This paper investigates how visible light filter photometry can identify surface features of rocky exoplanets, linking them to extremophile habitats on Earth, to aid in prioritizing targets for biosignature detection.

Contribution

It demonstrates the potential of using color-color diagrams in visible wavelengths to characterize exoplanet surfaces and identify extreme environments indicative of habitability.

Findings

Surface features can be distinguished remotely via color-color diagrams.

Different Earth-like environments occupy distinct color spaces in visible light.

This method can prioritize exoplanets for follow-up biosignature searches.

Abstract

The search for extrasolar planets has already detected rocky planets and several planetary candidates with minimum masses that are consistent with rocky planets in the habitable zone of their host stars. A low-resolution spectrum in the form of a color-color diagram of an exoplanet is likely to be one of the first post-detection quantities to be measured for the case of direct detection. In this paper, we explore potentially detectable surface features on rocky exoplanets and their connection to, and importance as, a habitat for extremophiles, as known on Earth. Extremophiles provide us with the minimum known envelope of environmental limits for life on our planet. The color of a planet reveals information on its properties, especially for surface features of rocky planets with clear atmospheres. We use filter photometry in the visible waveband as a first step in the characterization of rocky exoplanets to prioritize targets for follow-up spectroscopy. Many surface environments on Earth have characteristic albedos and occupy a different color space in the visible waveband (0.4-0.9 microns) that can be distinguished remotely. These detectable surface features can be linked to the extreme niches that support extremophiles on Earth and provide a link between geomicrobiology and observational astronomy. This paper explores how filter photometry can serve as a first step in characterizing Earth-like exoplanets for an aerobic as well as an anaerobic atmosphere, thereby prioritizing targets to search for atmospheric biosignatures. Key Words: Color-color, Habitability, Extrasolar terrestrial planet, Extreme environments, Extremophiles, Reflectivity.