PREDICTIONS OF THE ATMOSPHERIC COMPOSITION OF GJ 1132b

Abstract

GJ 1132b is a nearby Earth-sized exoplanet transiting an M dwarf, and is among the most highly characterizable small exoplanets currently known. In this paper,we study the interaction of a magma ocean with a water-rich atmosphere on GJ 1132b and determine that it must have begun with more than 5 wt% initial water in order to still retain a water-based atmosphere. We also determine the amount of O 2 that can build up in the atmosphere as a result of hydrogen dissociation and loss. We find that the magma ocean absorbs at most ∼10% of the O 2 produced, whereas more than 90% is lost to space through hydrodynamic drag. The most common outcome for GJ 1132b from our simulations is a tenuous atmosphere dominated by O 2 , though, for very large initial water abundances,atmospheres with several thousands of bars of O 2 are possible. A substantial steam envelope would indicate either the existence of an earlier H 2 envelope or low XUV flux over the system's lifetime. A steam atmosphere would also imply the continued existence of a magma ocean on GJ 1132b. Further modeling is needed to study the evolution of CO 2 or N 2 -rich atmospheres on GJ 1132b.

The habitability of planets orbiting M-dwarf stars

“…If measured spectroscopically in a planet's atmosphere, O 2 , or O 3 , along with methane (CH 4 )-which has been proposed to be more abundant and long lasting in the atmospheres of M-dwarf planets, due to the lower amounts of near-UV surface emission from these stars (Segura et al, 2005)-could be indicative of a possibly biogenic source of O 2 , such as oxygenic photosynthesis (Lovelock, 1965). However, much recent work has been done to identify abiotic sources of O 2 on M-dwarf planets (Tian et al, 2014;Wordsworth & Pierrehumbert, 2014;Domagal-Goldman et al, 2014;Gao et al, 2015;Harman et al, 2015;Tian, 2015;Schaefer et al, 2016;Barnes et al, 2016), and to also understand how to discriminate abiotic from biological sources using spectroscopic observations Gao et al, 2015;Harman et al, 2015;Schwieterman et al, 2015Schwieterman et al, , 2016bMeadows et al, 2016). Methane, in addition to its biological sources, can be produced by abiotic processes such as serpentinization (the alteration of rocks with the addition of water into the crystal structure of their minerals; e.g.…”

The Surface UV Environment on Planets Orbiting M Dwarfs: Implications for Prebiotic Chemistry and the Need for Experimental Follow-up

“…The lowest-mass Mdwarfs remain in this state for timescales ofup to ∼1 Gyr, and one might speculate whether planets orbiting such stars might receive NUV irradiation that ismore similarto planets orbiting Sunlike stars. However, the bolometric luminosity of such stars is also higher; planets in the mainsequence habitable zones of such stars are liable to be in a runaway greenhouse state during their pre-main-sequence evolution, with temperatures globally above the boiling point of water and possibly as high as 1000 K  (Ramirez & Kaltenegger 2014;Schaefer et al 2016). Hence, these objects will lack clement conditions for aqueous-phase prebiotic chemistry, and are unlikely to be habitable during this phase.…”

A Simple Analytical Model for Rocky Planet Interiors

“…Masses and radii of rocky exoplanets have been found for about a dozen cases (Figure 1), including Kepler-21b (Howell et al 2012;Lopez-Morales et al 2016), Kepler-20b (Gautier et al 2012;Buchhave et al 2016), COROT-7b (Leger et al 2009;Queloz et al 2009;Hatzes et al 2011;Wagner et al 2012;Haywood et al 2014;Barros et al 2014), HD219134b (Vogt et al 2015;Motalebi et al 2015), Kepler-10b (Batalha et al 2011;Wagner et al 2012;Dumusque et al 2014;Esteves et al 2015), Kepler-93b (Ballard et al 2014;Dressing et al 2015), Kepler36b (Carter et al 2012;Morton et al 2016), Kepler-78b (Pepe et al 2013;Grunblatt et al 2015), K-105c (Rowe et al 2014;Holczer et al 2016;Jontof-Hutter et al 2016), GJ 1132b (Berta-Thompson 2015; Schaefer et al 2016), and more are likely. Here we explore what other parameters can be further gleaned from this information.…”