Close-in Sub-Neptunes Reveal the Past Rotation History of Their Host Stars: Atmospheric Evolution of Planets in the HD 3167 and K2-32 Planetary Systems
Abstract
Planet atmospheric escape induced by high-energy stellar irradiation is a key phenomenon shaping the structure and evolution of planetary atmospheres. Therefore, the present-day properties of a planetary atmosphere are intimately connected with the amount of stellar flux received by a planet during its lifetime, thus with the evolutionary path of its host star. Using a recently developed analytic approximation based on hydrodynamic simulations for atmospheric escape rates, we track within a Bayesian framework the evolution of a planet as a function of stellar flux evolution history, constrained by the measured planetary radius. We find that the ideal objects for this type of study are close-in sub-Neptune-like planets, as they are highly affected by atmospheric escape, and yet retain a significant fraction of their primordial hydrogen-dominated atmospheres. Furthermore, we apply this analysis to the HD 3167 and K2-32 planetary systems. For HD 3167, we find that the most probable irradiation level at 150 Myr was between 40 and 130 times solar, corresponding to a rotation period of {1.78}-1.23+2.69 days. For K2-32, we find a surprisingly low irradiation level ranging between half and four times solar at 150 Myr. Finally, we show that for multi-planet systems, our framework enables one to constrain poorly known properties of individual planets.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- July 2019
- DOI:
- arXiv:
- arXiv:1906.12153
- Bibcode:
- 2019ApJ...879...26K
- Keywords:
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- planets and satellites: atmospheres;
- planets and satellites: gaseous planets;
- planets and satellites: individual: HD 3167b;
- HD 3167c;
- HD 3167d;
- planets and satellites: physical evolution;
- Astrophysics - Earth and Planetary Astrophysics
- E-Print:
- 23 pages, 20 figures, 2 tables
