From: LARRY KLAES (ljk4_at_msn.com)
Date: Sat Oct 27 2007 - 21:22:29 PDT
Ocean Planet or Thick Atmosphere: On the Mass-Radius Relationship for Solid
Exoplanets with Massive Atmospheres
Authors: E. R. Adams, S. Seager, L. Elkins-Tanton
(Submitted on 25 Oct 2007)
Abstract: The bulk composition of an exoplanet is commonly inferred from its
average density. For small planets, however, the average density is not
unique within the range of compositions. Variations of a number of important
planetary parameters--which are difficult or impossible to constrain from
measurements alone--produce planets with the same average densities but
widely varying bulk compositions. We find that adding a gas envelope
equivalent to 0.1%-10% of the mass of a solid planet causes the radius to
increase 5-60% above its gas-free value. A planet with a given mass and
radius might have substantial water ice content (a so-called ocean planet)
or alternatively a large rocky-iron core and some H and/or He.
For example, a wide variety of compositions can explain the observed radius
of GJ 436b, although all models require some H/He. We conclude that the
identification of water worlds based on the mass-radius relationship alone
is impossible unless a significant gas layer can be ruled out by other
means.
Comments: 5 pages, 3 figures, accepted to ApJ
Subjects: Astrophysics (astro-ph)
Cite as: arXiv:0710.4941v1 [astro-ph]
Submission history
From: Elisabeth Adams [view email]
[v1] Thu, 25 Oct 2007 19:51:39 GMT (275kb)
http://arxiv.org/abs/0710.4941
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