Protostars and Planets VI, Heidelberg, July 15-20, 2013
Direct Imaging Detectability of Tidally Heated ExoMoons (THEM)
Turner, Edwin L. (Princeton Univ.)
Peters, Mary Anne (Princeton Univ.)
Existing and planned ground and space based telescopes are capable of directly imaging plausible tidally heated exomoons orbiting gas-giant exoplanets. Tidally heated exomoons can plausibly be far more luminous than their host exoplanet and as much as 0.001 as bright as the system\'s stellar primary. Because emission from exomoons can be powered by tidal forces, their luminosities are independent of their separations from the system\'s stellar primary. Furthermore, high surface temperatures can occur in systems that are billions of years old. Tidally heated exomoons may thus be far easier targets for direct imaging studies than giant exoplanets which must be both young and at a large projected separation (typically at least tens of AU) from their primary to be accessible to direct imaging currently. For example, the (warm) Spitzer Space Telescope and the next generation of ground based instruments could detect an exomoon roughly the size of the Earth at a temperature of ~600 K and a distance ~5 parsecs in IR bands; in more favorable cases, detections are possible at distances of tens of parsecs. Future mid-infrared space telescopes, such as JWST and SPICA, will be capable of directly imaging tidally heated exomoons around the nearest two dozen stars with brightness temperatures of ~300 K and sizes similar to the Earth orbiting beyond 10 AU at a 5 sigma confidence level in a 10^4 second integration. If such exomoons exist and are sufficiently common (and thus nearby), it may be easier to directly image an exomoon with surface conditions that allow the existence of liquid water than it will be to resolve an Earth-like planet in the classical Habitable Zone from its primary.
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