Three regimes of extrasolar planet radius from host star metallicities

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Three regimes of extrasolar planet radius from host star metallicities

Post by Sirius_Alpha on 2nd June 2014, 8:21 pm

Three regimes of extrasolar planet radius inferred from host star metallicities
http://arxiv.org/abs/1405.7695

Approximately half of the extrasolar planets (exoplanets) with radii less than four Earth radii are in orbits with short periods1. Despite their sheer abundance, the compositions of such planets are largely unknown. The available evidence suggests that they range in composition from small, high-density rocky planets to low-density planets consisting of rocky cores surrounded by thick hydrogen and helium gas envelopes. Here we report the metallicities (that is, the abundances of elements heavier than hydrogen and helium) of more than 400 stars hosting 600 exoplanet candidates, and find that the exoplanets can be categorized into three populations defined by statistically distinct (~4.5σ) metallicity regions. We interpret these regions as reflecting the formation regimes of terrestrial-like planets (radii less than 1.7 Earth radii), gas dwarf planets with rocky cores and hydrogen–helium envelopes (radii between 1.7 and 3.9 Earth radii) and ice or gas giant planets (radii greater than 3.9 Earth radii). These transitions correspond well with those inferred from dynamical mass estimates2, 3, implying that host star metallicity, which is a proxy for the initial solids inventory of the protoplanetary disk, is a key ingredient regulating the structure of planetary systems.

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Re: Three regimes of extrasolar planet radius from host star metallicities

Post by Lazarus on 4th June 2014, 2:14 pm

Also some evidence towards the idea that gas accretion switches on at higher masses for planets in longer-period orbits.

Low metallicity favouring terrestrial planet formation would perhaps suggest that the galaxy could have formed habitable planets very early on. So where is everybody?

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Re: Three regimes of extrasolar planet radius from host star metallicities

Post by Lazarus on 27th January 2015, 5:57 pm

Then again, maybe not.

Schlaufman (arXiv 2015) "A Continuum of Planet Formation Between 1 and 4 Earth Radii"
http://arxiv.org/abs/1501.05953

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Re: Three regimes of extrasolar planet radius from host star metallicities

Post by Shellface on 27th January 2015, 8:34 pm

Statistics are complex, I guess.

I suppose the best way to interpret this is to say gaseous low-mass planets form out of the same conditions as terrestrial ones. Perhaps there may be some ancient atmospheres lurking somewhere in the solar neighbourhood.

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Re: Three regimes of extrasolar planet radius from host star metallicities

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