The XUV irradiation and likely atmospheric escape of the super-Earth π Men c
Abstract
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 characterization 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 L_X/L_bol = (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.
- Publication:
-
Monthly Notices of the Royal Astronomical Society
- Pub Date:
- March 2019
- DOI:
- 10.1093/mnrasl/slz003
- arXiv:
- arXiv:1901.01875
- Bibcode:
- 2019MNRAS.484L..49K
- Keywords:
-
- planet-star interactions;
- stars: individual: Pi Mensae;
- X-rays: stars;
- Astrophysics - Earth and Planetary Astrophysics;
- Astrophysics - Solar and Stellar Astrophysics
- E-Print:
- 5 pages, 3 figures, 3 tables