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J. A. Burns, M. Cuk (Cornell U.)
Many have hoped that satellites of giant planets might harbor life. However, satellites of close-in extrasolar planets, like those now being found may not survive. Here, in order to identify which bodies could be viable, we recall various mechanisms that may lead to the demise of satellites.
Orbits of satellites about nearby planets will decay by tides once the rotational periods of those planets are synchronized with their orbital periods by stellar tides (Barnes and O'Brien 2001). Objects further away can be lost by being driven away until they are gravitationally grasped by their star (Holman and Wiegert 1999).
Despite the scorching temperatures caused by their suns, close extrasolar planets can retain their atmospheres for long periods because escape velocities generally exceed thermal speeds. Such is not the case for their progeny, much smaller satellites with lesser escape velocities. Such objects lose their atmospheres and indeed vaporize once they get within a few stellar radii (Vokrouhlicky et al. 2000).
We introduce yet another loss mechanism, Yarkovsky decay. As satellites orbit a planet, re-emitted thermal radiation is larger when they are on the stellar-facing half of the orbit. This occurs for all satellites because they are hotter on that portion of the orbit. Thus, averaged over the orbit, objects that spin in the same sense as they orbit suffer a Yarkovsky-like drag force. In addition some close-orbiting satellites will go into eclipse and cool. The latter process has been investigated for Earth-orbiting spacecraft (Rubincam 1987). The former process has not previously been discussed to our knowledge. It is important for distant satellites, such as irregular ones, since their orbits are significant fractions of their planet's astrocentric ones.
Here we consider all these loss mechanisms to understand whether any satellites can survive.
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Bulletin of the American Astronomical Society, 34, #3< br> © 2002. The American Astronomical Soceity.