Ï€ 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​=(4.84−0.84+0.92​)×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.Comment: 5 pages, 3 figures, 3 tables; accepted for publication in MNRAS
Letter