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

Title: Acceleration of Cooling of Ice Giants by Condensation in Early Atmospheres

Abstract

The present infrared brightness of a planet originates partly from the accretion energy that the planet gained during its formation and hence provides important constraints to the planet formation process. A planet cools down from a hot initial state to the present state by losing energy through radiative emission from its atmosphere. Thus, the atmospheric properties affect the planetary cooling rate. Previous theories of giant planet cooling assume that the atmospheric composition is unchanged throughout the evolution. Planet formation theories, however, suggest that the atmospheres especially of ice giants are rich in heavy elements in the early stages. These heavy elements include condensable species such as H{sub 2}O, NH{sub 3}, and CH{sub 4}, which are expected to have a great impact on atmospheric temperature and thus on radiative emission through latent heat release. In this study we investigate the effect of such condensation on the planetary emission flux and quantify the impact on the cooling timescale. We then demonstrate that the latent heat of these species keeps the atmosphere hot and thus the emission flux high for billions of years, resulting in an acceleration of the cooling of ice giants. This sheds light on the long-standing problem that Uranus is much less bright thanmore » theoretically predicted and is different in brightness from Neptune in spite of the similarity in mass and radius. We also find that young ice giants with highly enriched atmospheres are much brighter in the mid-infrared than ice giants with non-enriched atmospheres. This provides important implications for future direct imaging of extrasolar ice giants.« less

Authors:
;  [1]
  1. Department of Earth and Planetary Science, Graduate School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033 (Japan)
Publication Date:
OSTI Identifier:
22663591
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astronomical Journal (Online); Journal Volume: 153; Journal Issue: 6; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ACCELERATION; AMMONIA; BRIGHTNESS; COOLING; EMISSION; EVOLUTION; ICE; LIMITING VALUES; MASS; METHANE; NEPTUNE PLANET; SATELLITE ATMOSPHERES; SATELLITES; URANUS PLANET; VISIBLE RADIATION

Citation Formats

Kurosaki, Kenji, and Ikoma, Masahiro, E-mail: kurosaki.k@nagoya-u.jp, E-mail: ikoma@eps.s.u-tokyo.ac.jp. Acceleration of Cooling of Ice Giants by Condensation in Early Atmospheres. United States: N. p., 2017. Web. doi:10.3847/1538-3881/AA6FAF.
Kurosaki, Kenji, & Ikoma, Masahiro, E-mail: kurosaki.k@nagoya-u.jp, E-mail: ikoma@eps.s.u-tokyo.ac.jp. Acceleration of Cooling of Ice Giants by Condensation in Early Atmospheres. United States. doi:10.3847/1538-3881/AA6FAF.
Kurosaki, Kenji, and Ikoma, Masahiro, E-mail: kurosaki.k@nagoya-u.jp, E-mail: ikoma@eps.s.u-tokyo.ac.jp. Thu . "Acceleration of Cooling of Ice Giants by Condensation in Early Atmospheres". United States. doi:10.3847/1538-3881/AA6FAF.
@article{osti_22663591,
title = {Acceleration of Cooling of Ice Giants by Condensation in Early Atmospheres},
author = {Kurosaki, Kenji and Ikoma, Masahiro, E-mail: kurosaki.k@nagoya-u.jp, E-mail: ikoma@eps.s.u-tokyo.ac.jp},
abstractNote = {The present infrared brightness of a planet originates partly from the accretion energy that the planet gained during its formation and hence provides important constraints to the planet formation process. A planet cools down from a hot initial state to the present state by losing energy through radiative emission from its atmosphere. Thus, the atmospheric properties affect the planetary cooling rate. Previous theories of giant planet cooling assume that the atmospheric composition is unchanged throughout the evolution. Planet formation theories, however, suggest that the atmospheres especially of ice giants are rich in heavy elements in the early stages. These heavy elements include condensable species such as H{sub 2}O, NH{sub 3}, and CH{sub 4}, which are expected to have a great impact on atmospheric temperature and thus on radiative emission through latent heat release. In this study we investigate the effect of such condensation on the planetary emission flux and quantify the impact on the cooling timescale. We then demonstrate that the latent heat of these species keeps the atmosphere hot and thus the emission flux high for billions of years, resulting in an acceleration of the cooling of ice giants. This sheds light on the long-standing problem that Uranus is much less bright than theoretically predicted and is different in brightness from Neptune in spite of the similarity in mass and radius. We also find that young ice giants with highly enriched atmospheres are much brighter in the mid-infrared than ice giants with non-enriched atmospheres. This provides important implications for future direct imaging of extrasolar ice giants.},
doi = {10.3847/1538-3881/AA6FAF},
journal = {Astronomical Journal (Online)},
number = 6,
volume = 153,
place = {United States},
year = {Thu Jun 01 00:00:00 EDT 2017},
month = {Thu Jun 01 00:00:00 EDT 2017}
}
  • In the present analysis of ice particle condensation in the vicinity of a cometary nucleus, the hydrodynamic equation solutions for ice particles and H/sub 2/O gas encompass the condensation and sublimation of ice particles as well as the energy exchange between ice particles and the gas in a dustless comet. The sublimation of condensed ice particles leads to a heating of ambient gas to temperatures higher than those predicted by previously proposed models. The results obtained reveal that the survival distance of ice particles against sublimation is longer than that of a previous calculation for a spacecraft encounter of Cometmore » Halley, but that the ice particle size is smaller due to a larger fraction of uncondensed H/sub 2/O gas. 18 references.« less
  • We have identified in an acid resistant residue of the carbonaceous chondrite Murchison a large number (458) of highly refractory metal nuggets (RMNs) that once were most likely hosted by Ca,Al-rich inclusions (CAIs). While osmium isotopic ratios of two randomly selected particles rule out a presolar origin, the bulk chemistry of 88 particles with sizes in the submicron range determined by energy dispersive X-ray (EDX) spectroscopy shows striking agreement with predictions of single-phase equilibrium condensation calculations. Both chemical composition and morphology strongly favor a condensation origin. Particularly important is the presence of structurally incompatible elements in particles with a single-crystalmore » structure, which also suggests the absence of secondary alteration. The metal particles represent the most pristine early solar system material found so far and allow estimation of the cooling rate of the gaseous environment from which the first solids formed by condensation. The resulting value of 0.5 K yr{sup -1} is at least 4 orders of magnitude lower than the cooling rate of molten CAIs. It is thus possible, for the first time, to see through the complex structure of most CAIs and infer the thermal history of the gaseous reservoir from which their components formed by condensation.« less
  • The lithium abundance in the atmospheres of eight giants of the spectral class K5-M3 has been determined with allowance for molecular absorption. Spectrograms of the stars were obtained using the 2.6-m telescope of the Crimean Astrophysical Observatory with reciprocal dispersion 6 A/mm. To take into account the molecular absorption, synthetic spectra in the region 6700-6710 A were calculated by means of Tsjui models (1978). The models include all known atomic lines and bands of the molecules TiO, CN, and ZrO. In the atmospheres of six of the eight stars there is a deficit of the lithium abundance in the atmospheremore » of 3 Aqr M3 III the lithium abundance has the solar value, while in 29 Cap M3 III a lithium excess is found.« less
  • Fifteen spectrograms of the M giants delta/sup 2/ Lyr and g Her obtained at 14-A/mm dispersion are analyzed. The physical parameters of the atmospheres at each epoch of observation are determined by means of curves of growth. The vibration temperature is estimated from the ..cap alpha..-system bands of TiO.