Pi Mensae c Atmosphere

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Pi Mensae c Atmosphere

Post by Sirius_Alpha on 7th January 2019, 9:50 pm

The XUV irradiation and likely atmospheric escape of the super-Earth π Men c

π Men c was recently announced as the first confirmed exoplanet from the TESS mission. The planet has a radius of just 2 R⊕ and it transits a nearby Sun-like star of naked-eye brightness, making it the ideal target for atmospheric characterisation of a super-Earth. Here we analyse archival ROSAT and Swift observations of π Men in order to determine the X-ray and extreme-ultraviolet irradiation of the planetary atmosphere and assess whether atmospheric escape is likely to be on-going. We find that π Men has a similar level of X-ray emission to the Sun, with LX/Lbol=(4.84+0.92−0.84)10−7. However, due to its small orbital separation, the high-energy irradiation of the super-Earth is around 2000 times stronger than suffered by the Earth. We show that this is sufficient to drive atmospheric escape at a rate greater than that readily detected from the warm Neptune GJ 436b. Furthermore, we estimate π Men to be four times brighter at Ly α than GJ 436. Given the small atmospheric scale heights of super-Earths, together with their potentially cloudy atmospheres, and the consequent difficulty in measuring transmission spectra, we conclude that ultraviolet absorption by material escaping π Men c presents the best opportunity currently to determine the atmospheric composition of a super-Earth.

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