Size distribution of observed and simulated exoplanets with radii smaller than five Earth radii (IMAGE)
Caption
The number of exoplanets decreases between 1.6 and 2.2, producing a pronounced valley in distribution. Instead, there are more planets present with sizes around 1.4 and 2.4 Earth radii. The latest simulations, which for the first time take realistic properties of water into account, indicate that icy planets that migrate into the interior of planetary systems form thick atmospheres of water vapour. It makes them appear larger than they would be at their place of origin. These produce the peak at around 2.4 Earth radii. At the same time, smaller rocky planets lose part of their original gas envelope over time, causing their measured radius to shrink and thus contributing to the accumulation at around 1.4 Earth radii.
Credit
R. Burn, C. Mordasini / MPIA
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