Hot Super Earths: Tidally Downsized hot jupiters? The hot jupiter around the metal poor star explained

Abstract

Recent Kepler observations revealed an unexpected abundance of "hot" Earth-size to Neptune-size planets in the inner ~0.02-0.2 AU from their parent stars. Another "oddity" of recent observations is the discovery of a hot jupiter planet around a very metal poor star of extragalactic origin. We point out that these observations have natural explanations in the framework of the Tidal Downsizing hypothesis, a new and an alternative model for planet formation. We show that disassociation of molecular hydrogen leads to the "second collapse" of the giant planet embryos. The collapse forms much denser fluid configurations, closely resembling isolated proto-giant planets on the Hayashi track before they enter the degenerate "main sequence" phase. We find that, in the early gas-rich phase of proto-planetary discs, these configurations migrate inward more rapidly than they contract. They are therefore tidally disrupted at characteristic distance of ~ 0.05 -0.1 AU from their parent stars. The disruption is likely to leave solid cores behind, which we identify with the hot Super-Earths observed by Kepler. In addition, we show that single hot jupiters (also found by the Kepler telescope) are not surprising in the context of TD hypothesis. Finally, formation of coreless giant planets by the second collapse of the giant embryos occurs for either very massive embryos (more than ~ 20 Jupiter masses) or very metal poor ones. We suggest that this process explains the extra-galactic hot jupiter.