Protostars and Planets VI, Heidelberg, July 15-20, 2013
Toward A Better Understanding Of Uranus & Neptune: Implications For Intermidiate-Mass Extrasolar Planets
Helled, Ravit (Tel-Aviv University)
The number of extrasolar planets with masses similar to those of Uranus and Neptune is increasing rapidly. It is clear that a better understanding of the formation mechanism, evolutionary path, and interior structure of this planetary population is desirable. Despite their distance from the Sun, Uranus and Neptune are the best representatives of this planet-class in our own Solar System, and although we have much more information available on Uranus and Neptune compared to extrasolar planets with similar masses, our understanding of Uranus and Neptune is still rather limited. While Uranus and Neptune are similar in mass (~ 14.5 and 17.1 M_Earth, respectively) they differ in other physical properties such as thermal emission, obliquity, and atmospheric enrichment. We present new interior models of Uranus and Neptune; using the Voyager 2 rotation periods it is found that the major difference between Uranus and Neptune in terms of internal structure is that Neptune requires a non-solar envelope, while Uranus is best matched with an envelope of solar composition. We also find that is possible to fit the gravitational moments of the planets without sharp compositional transitions (i.e. density discontinuities). However, when the uncertainty in rotation period and flattening of the planets is included, the derived internal structures of Uranus and Neptune can differ substantially. We suggest that Uranus and Neptune may not be \"twin planets\", and that it is possible that each planet represents a different “class” of planets in this mass range in terms of composition, internal structure, and possibly, formation mechanism.
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