Fundación Galileo Galilei - INAF Telescopio Nazionale Galileo 28°45'14.4N 17°53'20.6W 2387.2m A.S.L.

Seminars at FGG

Very Hot Super-Earths with Hydrogen Atmospheres: A Model Explaining Their Paradoxical Existence

Speaker: Darius Modirrousta (Observatory of Palermo - Italy)

Date and time: 2019-05-16 12:30

We propose a new model that could explain the survival of hydrogen atmospheres on hot super-Earths like 55 Cancri e. By individually analysing the mass-loss rates on the day-side and night-side of 55 Cancri e we show that a hydrogen envelop may only be possible on the dark side of the planet. By then considering the tidal locking and mass-loss timescales, together with the conservation of angular momentum, we derive several equations that constrain the initial (birth) masses of hot super-Earths. Our model predicts that 55 Cancri e formed with a day-length between approximately 17 − 18.5 hours and an initial mass less than ∼ 12M⊕ hence allowing it to become tidally locked before the complete destruction of its atmosphere. For comparison, CoRoT-7b, an exoplanet with very similar properties to 55 Cancri e but lacking an atmosphere, formed with a day-length significantly different from ∼ 20.5 hours whilst also having an initial mass smaller than ∼ 9M⊕. We state that the presence of a hydrogen atmosphere on a hot super-Earth may be strongly dependent on its initial properties; the initial mass, day-length and orbital distance from the host star.