37th DPS Meeting, 4-9 September 2005
Session 30 Outer Planets
Poster, Tuesday, September 6, 2005, 6:00-7:15pm, Music Lecture Room 5

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[30.02] Constraining the Gravitational Energies of Uranus and Neptune from Interior Models: Implications for Formation

A. M. Cody, D. J. Stevenson (Caltech)

Although observational data on Uranus and Neptune has improved our picture of these planets in recent years, knowledge of their compositional structure and origin remains incomplete. Measurements of the gravitational moments have revealed that a layered configuration consisting of distinct rock, ice, and gas components is unlikely. Instead, partially "mixed" interior density profiles appear to be more consistent with the data. This partial mixing is too great to be explained by thermal convection stirring material upwards. It must therefore be of primordial origin and diagnostic of the mass spectrum of solid bodies that accreted and the timing of the outer envelope gas accumulation. The partial mixing is expressed quantitatively by the difference between the gravitational energy of a fully differentiated planet and the actual gravitational energy. Given plausible density profiles, we explore what limits may be placed on the planets' gravitational energy based on the observed J2 and J4 values. For many conceivable models, there is a strong correlation between J2 and the gravitational energy. Hence we argue that J2 (in conjunction with J4 and the need to run a dynamo) may be used to constrain the initial formation process.

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Bulletin of the American Astronomical Society, 37 #3
© 2004. The American Astronomical Soceity.