Moving the Orbits of Planets

David Jewitt ^ | Last updated Sep 2004 | David Jewitt

[SunkenCiv]

Meanwhile, the Doppler discovery of extrasolar planets orbiting very close to their parent stars has raised a different problem. Many of the planets are so close to their stars (<0.1 AU), and so hot, that they cannot be supposed to have formed where we now observe them. By inference, they could have formed at larger distances (several AU) and then migrated inwards. What would cause this inward migration? As with the solar system case, the root cause may be an exchange of angular momentum with material surrounding the planets at their formation. In particular, if the extrasolar planets formed in massive disks, then torques between the planets and the disks could drive the former inwards.

Aha, you say, why did they stop? There are several possible answers to this question (including the most brutally honest one "we don't know"). Indeed, they might not have stopped, in the sense that the observed close-in extrasolar planets could be the survivors from a now-defunct armada of planets that plopped into their stars never to be seen again. In this case, what we see is what was left behind after the planetary accretion disk dissipated and the tidal torques disappeared. Another possibility is that inward migration stopped when the planets reached the inner edge of the planetary accretion disk, because then the torques acting to propel them inwards would vanish.

[SunkenCiv]

Note: this topic is from 02/02/2006. Just an update.

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