Formation of secondary atmospheres on terrestrial planets by late disk accretion

Abstract

Recently, gas disks have been discovered around main sequence stars well beyond the usual protoplanetary disk lifetimes (i.e., > 10 Myrs), when planets have already formed. These gas disks, mainly composed of CO, carbon, and oxygen seem to be ubiquitous in systems with planetesimal belts (similar to our Kuiper belt), and can last for hundreds of millions of years. Planets orbiting in these gas disks will accrete a large quantity of gas that will transform their primordial atmospheres into new secondary atmospheres with compositions similar to that of the parent gas disk. Here, we quantify how large a secondary atmosphere can be created for a variety of observed gas disks and for a wide range of planet types. We find that gas accretion in this late phase is very significant and an Earth's atmospheric mass of gas is readily accreted on terrestrial planets in very tenuous gas disks. In slightly more massive disks, we show that massive CO atmospheres can be accreted, forming planets with up to sub-Neptune-like pressures. Our new results demonstrate that new secondary atmospheres with high metallicities and high C/O ratios will be created in these late gas disks, resetting their primordial compositions inherited from the protoplanetary disk phase, and providing a new birth to planets that lost their atmosphere to photoevaporation or giant impacts. We therefore propose a new paradigm for the formation of atmospheres on low-mass planets, which can be tested with future observations (JWST, ELT, ARIEL). We also show that this late accretion would show a very clear signature in Sub-Neptunes or cold exo-Jupiters. Finally, we find that accretion creates cavities in late gas disks, which could be used as a new planet detection method, for low mass planets a few au to a few tens of au from their host stars.

Paper accepted and now published in Nature Astronomy. See the published version here: https://www.nature.com/articles/s41550-020-1050-2

References in corpus (18)

• Two accreting protoplanets around the young star PDS 70
• Detection of Carbon Monoxide and Water Absorption Lines in an Exoplanet Atmosphere
• Water Vapour Absorption in the Clear Atmosphere of an exo-Neptune
• Make Super-Earths, Not Jupiters: Accreting Nebular Gas onto Solid Cores at 0.1 AU and Beyond
• Observing the Atmospheres of Known Temperate Earth-sized Planets with JWST
• A Sub-Neptune Exoplanet with a Low-Metallicity Methane-Depleted Atmosphere and Mie-Scattering Clouds
• Molecular Gas Clumps from the Destruction of Icy Bodies in the $\beta$ Pictoris Debris Disk
• HAT-P-26b: A Neptune-Mass Exoplanet with a Well Constrained Heavy Element Abundance
• Hydrodynamics of Embedded Planets' First Atmospheres. II. A Rapid Recycling of Atmospheric Gas
• Collisional processes and size distribution in spatially extended debris discs
• Peering into the formation history of beta Pictoris b with VLTI/GRAVITY long baseline interferometry
• Detection of exocometary CO within the 440 Myr-old Fomalhaut belt: a similar CO+CO${}_2$ ice abundance in exocomets and Solar System comets
• Debris Disks in the Scorpius-Centaurus OB Association Resolved by ALMA
• Molecular gas in debris disks around young A-type stars
• Late veneer and late accretion to the terrestrial planets
• Population synthesis of exocometary gas around A stars
• On the Ubiquity and Stellar Luminosity Dependence of Exocometary CO Gas: Detection around M Dwarf TWA 7
• Envelopes of embedded super-Earths II. Three-dimensional isothermal simulations

Cited by in corpus (16)

• Vertically resolved magma ocean-protoatmosphere evolution: H${}_2$, H${}_2$O, CO${}_2$, CH${}_4$, CO, O${}_2$, and N${}_2$ as primary absorbers
• Formation and dynamics of water clouds on temperate sub-Neptunes: The example of K2-18b
• Caught in the Act: Core-powered Mass-loss Predictions for Observing Atmospheric Escape
• Exocomets from a Solar System Perspective
• Survey of planetesimal belts with ALMA: gas detected around the Sun-like star HD 129590
• Primordial or Secondary? Testing models of debris disk gas with ALMA
• Vertical evolution of exocometary gas: I. How vertical diffusion shortens the CO lifetime
• A molecular wind blows out of the Kuiper belt
• X-Shooter Survey of Young Intermediate Mass Stars -- I. Stellar Characterization and Disc Evolution
• Stellar winds can affect gas dynamics in debris disks and create observable belt winds
• Abundance analysis of stars hosting gas-rich debris disks
• The ALMA survey to Resolve exoKuiper belt Substructures (ARKS) VIII: A dust arc and non-Keplerian gas kinematics in HD 121617
• Discovery of carbon monoxide emission from five debris disks around young A-type stars
• Late gas released in the young Kuiper belt could have significantly contributed to the carbon enrichment of the atmospheres of Neptune and Uranus
• The formation of planetary systems with SPICA
• Resolving the large exoKuiper belt of the HD 126062 debris disc and extended gas emission in its vicinity