TY - JOUR
T1 - Retrieval of water in Jupiter's deep atmosphere using microwave spectra of its brightness temperature
AU - de Pater, Imke
AU - DeBoer, David
AU - Marley, Mark
AU - Freedman, Richard
AU - Young, Richard
N1 - Funding Information:
We thank W.J. Welch for discussions during our research, and P.N. Romani for his help with some of the model calculations. We further thank A. Ingersoll and an anonymous referee for their help in improving the paper. We thank M.A. Janssen for valuable discussions and exchange of manuscripts prior to publication. We further thank T. Hanley and P.G. Steffes for fruitful discussions regarding absorption by water vapor. Because of the uncertainties in the water absorption profile under jovian conditions, they started laboratory experiments to determine an accurate profile for water in a high-pressure H 2 He environment. I.d.P. thanks the Miller Institute for Basic Research in Science at the University of California in Berkeley for support. This work was further funded in part by NASA grant NAG5-12062 to the University of California, Berkeley.
PY - 2005/2
Y1 - 2005/2
N2 - Despite several spacecraft encounters and numerous groundbased investigations, we still do not know much about Jupiter's deep atmosphere; in fact, the Galileo probe results were so different than anyone had anticipated, that we understand even less about this planet's atmosphere now than before the Galileo mission. We formulate four basic questions in Section 1.3, which, if solved, would help to better understand the chemistry and dynamics in Jupiter's atmosphere. We believe that three out of the four questions (explanation of NH3 altitude profile, characterization of hot spots, altitude below which the atmosphere is uniformly mixed) may be solved from passive sounding of Jupiter's deep (∼ tens of bars) atmosphere via a radio telescope orbiting the planet. Question nr. 4 (the water abundance in Jupiter's deep atmosphere) has been singled out by the Solar System Exploration Decadal Survey as a key question, since the water abundance in Jupiter's deep atmosphere is tied in with planet formation models. In this paper we investigate the sensitivity of microwave retrievals to the composition of Jupiter's deep atmosphere, in particular the water abundance. Based upon present uncertainties in the ammonia abundance and other known and unknown absorbers, including uncertainties in clouds (density and index of refraction), and uncertainties in the thermal structure and lineshape profiles, we conclude that the retrieval of water at depth from microwave spectra (disk-averaged and locally) will be highly uncertain. We show that, if the H2O lineshape profile would be accurately known (laboratory data are needed!), an atmosphere with a near-solar H2O abundance can likely be distinguished from one with an abundance of 10-20×solar O based upon the difference in their microwave spectra at wavelengths ≳ 50 cm. This would be sufficient to distinguish between some proposed scenarios by which Jupiter acquired its inventory of volatile elements heavier than helium. If, in addition, limb-darkening measurements are obtained (again, the H2O lineshape profile should be known), tighter constraints on the H2O abundance can be obtained (see also Janssen et al., 2004, this issue).
AB - Despite several spacecraft encounters and numerous groundbased investigations, we still do not know much about Jupiter's deep atmosphere; in fact, the Galileo probe results were so different than anyone had anticipated, that we understand even less about this planet's atmosphere now than before the Galileo mission. We formulate four basic questions in Section 1.3, which, if solved, would help to better understand the chemistry and dynamics in Jupiter's atmosphere. We believe that three out of the four questions (explanation of NH3 altitude profile, characterization of hot spots, altitude below which the atmosphere is uniformly mixed) may be solved from passive sounding of Jupiter's deep (∼ tens of bars) atmosphere via a radio telescope orbiting the planet. Question nr. 4 (the water abundance in Jupiter's deep atmosphere) has been singled out by the Solar System Exploration Decadal Survey as a key question, since the water abundance in Jupiter's deep atmosphere is tied in with planet formation models. In this paper we investigate the sensitivity of microwave retrievals to the composition of Jupiter's deep atmosphere, in particular the water abundance. Based upon present uncertainties in the ammonia abundance and other known and unknown absorbers, including uncertainties in clouds (density and index of refraction), and uncertainties in the thermal structure and lineshape profiles, we conclude that the retrieval of water at depth from microwave spectra (disk-averaged and locally) will be highly uncertain. We show that, if the H2O lineshape profile would be accurately known (laboratory data are needed!), an atmosphere with a near-solar H2O abundance can likely be distinguished from one with an abundance of 10-20×solar O based upon the difference in their microwave spectra at wavelengths ≳ 50 cm. This would be sufficient to distinguish between some proposed scenarios by which Jupiter acquired its inventory of volatile elements heavier than helium. If, in addition, limb-darkening measurements are obtained (again, the H2O lineshape profile should be known), tighter constraints on the H2O abundance can be obtained (see also Janssen et al., 2004, this issue).
KW - Atmosphere
KW - Jupiter
KW - Radiative transfer
KW - Radio observations
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U2 - 10.1016/j.icarus.2004.06.019
DO - 10.1016/j.icarus.2004.06.019
M3 - Article
AN - SCOPUS:14044252812
SN - 0019-1035
VL - 173
SP - 425
EP - 438
JO - Icarus
JF - Icarus
IS - 2
ER -