skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: CARBON-RICH GIANT PLANETS: ATMOSPHERIC CHEMISTRY, THERMAL INVERSIONS, SPECTRA, AND FORMATION CONDITIONS

Abstract

The recent inference of a carbon-rich atmosphere, with C/O {>=} 1, in the hot Jupiter WASP-12b motivates the exotic new class of carbon-rich planets (CRPs). We report a detailed study of the atmospheric chemistry and spectroscopic signatures of carbon-rich giant (CRG) planets, the possibility of thermal inversions in their atmospheres, the compositions of icy planetesimals required for their formation via core accretion, and the apportionment of ices, rock, and volatiles in their envelopes. Our results show that CRG atmospheres probe a unique region in composition space, especially at high temperature (T). For atmospheres with C/O {>=} 1, and T {approx}> 1400 K in the observable atmosphere, most of the oxygen is bound up in CO, while H{sub 2}O is depleted and CH{sub 4} is enhanced by up to two or three orders of magnitude each, compared to equilibrium compositions with solar abundances (C/O = 0.54). These differences in the spectroscopically dominant species for the different C/O ratios cause equally distinct observable signatures in the spectra. As such, highly irradiated transiting giant exoplanets form ideal candidates to estimate atmospheric C/O ratios and to search for CRPs. We also find that the C/O ratio strongly affects the abundances of TiO and VO,more » which have been suggested to cause thermal inversions in highly irradiated hot Jupiter atmospheres. A C/O = 1 yields TiO and VO abundances of {approx}100 times lower than those obtained with equilibrium chemistry assuming solar abundances, at P {approx} 1 bar. Such a depletion is adequate to rule out thermal inversions due to TiO/VO even in the most highly irradiated hot Jupiters, such as WASP-12b. We estimate the compositions of the protoplanetary disk, the planetesimals, and the envelope of WASP-12b, and the mass of ices dissolved in the envelope, based on the observed atmospheric abundances. Adopting stellar abundances (C/O = 0.44) for the primordial disk composition and low-temperature formation conditions (T {approx}< 30 K) for WASP-12b lead to a C/O ratio of 0.27 in accreted planetesimals, and, consequently, in the planet's envelope. In contrast, a C/O ratio of 1 in the envelope of WASP-12b requires a substantial depletion of oxygen in the disk, i.e., by a factor of {approx}0.41 for the same formation conditions. This scenario also satisfies the constraints on the C/H and O/H ratios reported for WASP-12b. If, alternatively, hotter conditions prevailed in a stellar composition disk such that only H{sub 2}O is condensed, the remaining gas can potentially have a C/O {approx} 1. However, a high C/O in WASP-12b caused predominantly by gas accretion would preclude superstellar C/H ratios which also fit the data.« less

Authors:
 [1];  [2];  [3]
  1. Department of Astrophysical Sciences, Princeton University, Princeton, NJ 08544 (United States)
  2. Institut UTINAM, CNRS-UMR 6213, Observatoire de Besancon, BP 1615, F-25010 Besancon Cedex (France)
  3. Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109 (United States)
Publication Date:
OSTI Identifier:
22004380
Resource Type:
Journal Article
Journal Name:
Astrophysical Journal
Additional Journal Information:
Journal Volume: 743; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA); Journal ID: ISSN 0004-637X
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ABUNDANCE; ASTROPHYSICS; ATMOSPHERIC CHEMISTRY; BORON 12; CARBON; JUPITER PLANET; METHANE; OXYGEN; PLANETARY ATMOSPHERES; PROTOPLANETS; SATELLITES; TEMPERATURE INVERSIONS; TITANIUM OXIDES; VANADIUM OXIDES; WATER

Citation Formats

Madhusudhan, Nikku, Mousis, Olivier, Johnson, Torrence V, and Lunine, Jonathan I., E-mail: nmadhu@astro.princeton.edu. CARBON-RICH GIANT PLANETS: ATMOSPHERIC CHEMISTRY, THERMAL INVERSIONS, SPECTRA, AND FORMATION CONDITIONS. United States: N. p., 2011. Web. doi:10.1088/0004-637X/743/2/191.
Madhusudhan, Nikku, Mousis, Olivier, Johnson, Torrence V, & Lunine, Jonathan I., E-mail: nmadhu@astro.princeton.edu. CARBON-RICH GIANT PLANETS: ATMOSPHERIC CHEMISTRY, THERMAL INVERSIONS, SPECTRA, AND FORMATION CONDITIONS. United States. https://doi.org/10.1088/0004-637X/743/2/191
Madhusudhan, Nikku, Mousis, Olivier, Johnson, Torrence V, and Lunine, Jonathan I., E-mail: nmadhu@astro.princeton.edu. Tue . "CARBON-RICH GIANT PLANETS: ATMOSPHERIC CHEMISTRY, THERMAL INVERSIONS, SPECTRA, AND FORMATION CONDITIONS". United States. https://doi.org/10.1088/0004-637X/743/2/191.
@article{osti_22004380,
title = {CARBON-RICH GIANT PLANETS: ATMOSPHERIC CHEMISTRY, THERMAL INVERSIONS, SPECTRA, AND FORMATION CONDITIONS},
author = {Madhusudhan, Nikku and Mousis, Olivier and Johnson, Torrence V and Lunine, Jonathan I., E-mail: nmadhu@astro.princeton.edu},
abstractNote = {The recent inference of a carbon-rich atmosphere, with C/O {>=} 1, in the hot Jupiter WASP-12b motivates the exotic new class of carbon-rich planets (CRPs). We report a detailed study of the atmospheric chemistry and spectroscopic signatures of carbon-rich giant (CRG) planets, the possibility of thermal inversions in their atmospheres, the compositions of icy planetesimals required for their formation via core accretion, and the apportionment of ices, rock, and volatiles in their envelopes. Our results show that CRG atmospheres probe a unique region in composition space, especially at high temperature (T). For atmospheres with C/O {>=} 1, and T {approx}> 1400 K in the observable atmosphere, most of the oxygen is bound up in CO, while H{sub 2}O is depleted and CH{sub 4} is enhanced by up to two or three orders of magnitude each, compared to equilibrium compositions with solar abundances (C/O = 0.54). These differences in the spectroscopically dominant species for the different C/O ratios cause equally distinct observable signatures in the spectra. As such, highly irradiated transiting giant exoplanets form ideal candidates to estimate atmospheric C/O ratios and to search for CRPs. We also find that the C/O ratio strongly affects the abundances of TiO and VO, which have been suggested to cause thermal inversions in highly irradiated hot Jupiter atmospheres. A C/O = 1 yields TiO and VO abundances of {approx}100 times lower than those obtained with equilibrium chemistry assuming solar abundances, at P {approx} 1 bar. Such a depletion is adequate to rule out thermal inversions due to TiO/VO even in the most highly irradiated hot Jupiters, such as WASP-12b. We estimate the compositions of the protoplanetary disk, the planetesimals, and the envelope of WASP-12b, and the mass of ices dissolved in the envelope, based on the observed atmospheric abundances. Adopting stellar abundances (C/O = 0.44) for the primordial disk composition and low-temperature formation conditions (T {approx}< 30 K) for WASP-12b lead to a C/O ratio of 0.27 in accreted planetesimals, and, consequently, in the planet's envelope. In contrast, a C/O ratio of 1 in the envelope of WASP-12b requires a substantial depletion of oxygen in the disk, i.e., by a factor of {approx}0.41 for the same formation conditions. This scenario also satisfies the constraints on the C/H and O/H ratios reported for WASP-12b. If, alternatively, hotter conditions prevailed in a stellar composition disk such that only H{sub 2}O is condensed, the remaining gas can potentially have a C/O {approx} 1. However, a high C/O in WASP-12b caused predominantly by gas accretion would preclude superstellar C/H ratios which also fit the data.},
doi = {10.1088/0004-637X/743/2/191},
url = {https://www.osti.gov/biblio/22004380}, journal = {Astrophysical Journal},
issn = {0004-637X},
number = 2,
volume = 743,
place = {United States},
year = {2011},
month = {12}
}