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Title: Steamworlds: Atmospheric Structure and Critical Mass of Planets Accreting Icy Pebbles

Abstract

In the core accretion model, gas-giant planets first form a solid core, which then accretes gas from a protoplanetary disk when the core exceeds a critical mass. Here, we model the atmosphere of a core that grows by accreting ice-rich pebbles. The ice fraction of pebbles evaporates in warm regions of the atmosphere, saturating it with water vapor. Excess water precipitates to lower altitudes. Beneath an outer radiative region, the atmosphere is convective, following a moist adiabat in saturated regions due to water condensation and precipitation. Atmospheric mass, density, and temperature increase with core mass. For nominal model parameters, planets with core masses (ice + rock) between 0.08 and 0.16 Earth masses have surface temperatures between 273 and 647 K and form an ocean. In more massive planets, water exists as a supercritical convecting fluid mixed with gas from the disk. Typically, the core mass reaches a maximum (the critical mass) as a function of the total mass when the core is 2–5 Earth masses. The critical mass depends in a complicated way on pebble size, mass flux, and dust opacity due to the occasional appearance of multiple core-mass maxima. The core mass for an atmosphere of 50% hydrogen andmore » helium may be a more robust indicator of the onset of gas accretion. This mass is typically 1–3 Earth masses for pebbles that are 50% ice by mass, increasing with opacity and pebble flux and decreasing with pebble ice/rock ratio.« less

Authors:
 [1]
  1. Carnegie Institution for Science Department of Terrestrial Magnetism, 5241 Broad Branch Road, NW, Washington, DC 20015 (United States)
Publication Date:
OSTI Identifier:
22679712
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 849; Journal Issue: 1; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ALTITUDE; ATMOSPHERIC PRECIPITATIONS; COSMIC DUST; CRITICAL MASS; DENSITY; HELIUM; HYDROGEN; ICE; OPACITY; PLANETS; PRECIPITATION; PROTOPLANETS; SATELLITE ATMOSPHERES; SATELLITES; SOLIDS; SURFACES; WATER VAPOR

Citation Formats

Chambers, John, E-mail: jchambers@carnegiescience.edu. Steamworlds: Atmospheric Structure and Critical Mass of Planets Accreting Icy Pebbles. United States: N. p., 2017. Web. doi:10.3847/1538-4357/AA91D0.
Chambers, John, E-mail: jchambers@carnegiescience.edu. Steamworlds: Atmospheric Structure and Critical Mass of Planets Accreting Icy Pebbles. United States. doi:10.3847/1538-4357/AA91D0.
Chambers, John, E-mail: jchambers@carnegiescience.edu. Wed . "Steamworlds: Atmospheric Structure and Critical Mass of Planets Accreting Icy Pebbles". United States. doi:10.3847/1538-4357/AA91D0.
@article{osti_22679712,
title = {Steamworlds: Atmospheric Structure and Critical Mass of Planets Accreting Icy Pebbles},
author = {Chambers, John, E-mail: jchambers@carnegiescience.edu},
abstractNote = {In the core accretion model, gas-giant planets first form a solid core, which then accretes gas from a protoplanetary disk when the core exceeds a critical mass. Here, we model the atmosphere of a core that grows by accreting ice-rich pebbles. The ice fraction of pebbles evaporates in warm regions of the atmosphere, saturating it with water vapor. Excess water precipitates to lower altitudes. Beneath an outer radiative region, the atmosphere is convective, following a moist adiabat in saturated regions due to water condensation and precipitation. Atmospheric mass, density, and temperature increase with core mass. For nominal model parameters, planets with core masses (ice + rock) between 0.08 and 0.16 Earth masses have surface temperatures between 273 and 647 K and form an ocean. In more massive planets, water exists as a supercritical convecting fluid mixed with gas from the disk. Typically, the core mass reaches a maximum (the critical mass) as a function of the total mass when the core is 2–5 Earth masses. The critical mass depends in a complicated way on pebble size, mass flux, and dust opacity due to the occasional appearance of multiple core-mass maxima. The core mass for an atmosphere of 50% hydrogen and helium may be a more robust indicator of the onset of gas accretion. This mass is typically 1–3 Earth masses for pebbles that are 50% ice by mass, increasing with opacity and pebble flux and decreasing with pebble ice/rock ratio.},
doi = {10.3847/1538-4357/AA91D0},
journal = {Astrophysical Journal},
number = 1,
volume = 849,
place = {United States},
year = {Wed Nov 01 00:00:00 EDT 2017},
month = {Wed Nov 01 00:00:00 EDT 2017}
}