* Astronomy

Title: Colours of extreme exoEarth environments
Authors: Siddharth Hegde, Lisa Kaltenegger

Context. 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 colour-colour diagram of an exoplanet is likely to be one of the first post-detection quantities to be measured for the case of direct detection.
Aims. 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.
Methods. The colour 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 as a first step in the characterisation of rocky exoplanets to prioritise targets for follow up spectroscopy.
Results. Many surface environments on Earth have characteristic albedos and occupy a different colour space in the visible waveband (0.4 to 0.9 micron) that can be distinguished remotely. These detectable surface features can be linked to the extreme niches that support extremophiles on Earth and provides a link between geomicrobiology and observational astronomy. This paper explores how filter photometry can serve as a first step in characterising Earth-like exoplanets for an aerobic as well as an anaerobic atmosphere thereby prioritising targets to search for atmospheric biosignatures.

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