The XUV irradiation and likely atmospheric escape of the super-Earth π Men c. (9th January 2019)

• Record Type: Journal Article
• Authors: King, George W; Wheatley, Peter J; Bourrier, Vincent; Ehrenreich, David
• Is Part Of: Monthly notices of the Royal Astronomical Society. Volume 484:Number 1(2019)
• Page Start: L49
• Page End: L53
• Publication Date: 2019-01-09
• Subjects: planet–star interactions -- stars: individual: Pi Mensae -- X-rays: stars; Astronomy -- Research -- Periodicals; Periodicals; 520.5
• DOI: 10.1093/mnrasl/slz003
• Languages: English
• ISSNs: 1745-3933

Abstract

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 $L_{\rm X}/L_{\rm bol} = (4.84^{+0.92}_{-0.84})\times 10^{-7}$ . 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.