Composition Effect on Mass-Radius Relation of Exoplanets

Allona Vazan, A. Kovetz, M. Podolak, Ravit Helled

Research output: Chapter in Book/Report/Conference proceedingConference contribution


In order to characterize the many hundreds of exoplanets that have been discovered, it is necessary to determine
their internal structure and composition. For many exoplanets, masses and radii are available. The radius-mass
relation can be substantially affected by the composition of the high-Z material, its mass fraction and its distribution within the planet. Adding high-Z material to a planet changes the density, energy and entropy profiles inside
the planet, and contributes to the opacity as well. Therefore, in certain conditions the heat transfer and luminosity
(and therefore contraction timescale) are also determined by the composition.
Here we model the evolution of giant and intermediate mass planets with various compositions and structures. We
investigate the effects of the composition and its depth dependence on the long-term evolution of the planets. We
study the influences of the heavy components, like rocks and ices, on the evolution of the planets by considering
their contribution to the energy and also to the opacity. We calculate the EOS for a mixture of hydrogen and
helium with heavy element for each of the planetary layers, and tie the grain opacity to the atmospheric metallicity
in a self-consistent manner. The effect of stellar irradiation is also considered.
We find that the most important effect is that of the grain opacity due to the additional high-Z material in the
envelope. This has the potential of increasing the computed radius of the planet by several tens of percent. The
changes in radius due to various compositions and stellar irradiation also affect the planetary contraction but
are found to be less important than the opacity effects. We suggest that the mass-radius relationship used for
characterization of observed exoplanets should be taken with great caution since different physical conditions can
result in very different mass-radius relationships.
Moreover, assuming constant composition distribution inside the planet in time is not necessarily correct. We
calculate mass redistribution processes, like core erosion by convection, during the planetary evolution, for
different initial assumptions. We show effects of mass redistribution on the inner structure and mass-radius
relationship of exoplanets
Original languageEnglish
Title of host publicationEGU General Assembly Conference Abstracts
Number of pages1
StatePublished - 1 May 2014

Publication series

NameEGU General Assembly Conference Abstracts


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