Photochemically driven collapse of Titan's atmosphere

Science

Volumn 275, Issue 5300, 1997, Pages 642-644

  Lorenz, Ralph D ^a   McKay, Christopher P ^b   Lunine, Jonathan I ^a  

^a UNIVERSITY OF ARIZONA   (United States)

^b NASA AMES RESEARCH CENTER   (United States)

Author keywords

[No Author keywords available]

Indexed keywords

ABSORPTION; ARTICLE; ASTRONOMY; ATMOSPHERE; CLIMATE; EVOLUTION; PHOTOLYSIS; PRIORITY JOURNAL;

ATMOSPHERE; EVOLUTION, PLANETARY; EXTRATERRESTRIAL ENVIRONMENT; METHANE; NITROGEN; PHOTOLYSIS; SATURN; TEMPERATURE;

EID: 0031053361     PISSN: 00368075     EISSN: None     Source Type: Journal    
DOI: 10.1126/science.275.5300.642     Document Type: Article

References (35)

1. The effective temperature is that temperature at which a black body would emit the total solar radiation absorbed by Titan. The temperature is estimated at 82 K at present (3).
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3. C. P. McKay, J. B. Pollack, and R. Courtin [Science 253, 1118 (1991)] described the haze greenhouse and antigreenhouse effects. R. E. Samuelson [Icarus 53, 364 (1983)] presented an analytic model illustrating stratospheric heating by haze absorption and greenhouse warming by tropospheric IR opacity.
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11. 4 seas and lakes, even if no such deposits are present now. Certainly, remote sensing data [for example, D. O. Muhleman, A. W. Grossman, B. J. Butler, M. A. Slade, Science 248, 975 (1990)] rule out global hydrocarbon deposits deeper than a few tens of meters.
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13. 4 atmospheric abundance, yet it still has a photochemical haze, although one that is about 1000 times optically thinner than Titan's present one.
14. Our model does not include all the minor opacity sources that may be present, so exactly how cold the stratosphere gets cannot be stated with certainty.
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16. -1 at most. Nitrogen drops are somewhat denser and can fall slightly faster. However, the time for a drop to grow to a few millimeters in diameter is short compared with the time (∼1 hour) for such a drop to fall a kilometer or two.
17. -2, globally averaged); in fact, comparing the radiative flux imbalance suggests the latent heat flux is actually smaller.
18. To investigate the effect of condensation on the thermal structure [see also J. L. Kasting, Icarus 94, 1 (1991)], we replaced the convective lower region in the atmosphere with one held to the saturation vapor curve. The radiative solution is recomputed, and the layer immediately above the saturated region is tested for saturation. If its temperature is lower than the saturation temperature for that pressure, the forced saturated region is extended one layer upward and the process repeated until convergence is achieved. The atmosphere is 30 layers deep, with layers varying in thickness from about 1 km near the surface, to about 15 km at the top (typically 300 km or so, where the pressure is less than 1 mbar).
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25. -1.
26. -1 of which about a quarter is transported by ocean currents; see, for example, R. Mcllveen, Fundamentals of Weather and Climate (Chapman & Hall, London, 1992). Titan's probably cratered landscape may prevent large-scale liquid motions [S. F. Dermott and C. Sagan, Nature 374, 238 (1995)], confining liquids to lakes [R. D. Lorenz, Planet. Space Sci. 42, 1 (1994)].
27. -1 of which about a quarter is transported by ocean currents; see, for example, R. Mcllveen, Fundamentals of Weather and Climate (Chapman & Hall, London, 1992). Titan's probably cratered landscape may prevent large-scale liquid motions [S. F. Dermott and C. Sagan, Nature 374, 238 (1995)], confining liquids to lakes [R. D. Lorenz, Planet. Space Sci. 42, 1 (1994)].
28. -1 of which about a quarter is transported by ocean currents; see, for example, R. Mcllveen, Fundamentals of Weather and Climate (Chapman & Hall, London, 1992). Titan's probably cratered landscape may prevent large-scale liquid motions [S. F. Dermott and C. Sagan, Nature 374, 238 (1995)], confining liquids to lakes [R. D. Lorenz, Planet. Space Sci. 42, 1 (1994)].
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32. W. R. Thompson, J. A. Zollweg, D. H. Gabis, Icarus 97, 187 (1992); L. C. Kouvaris and F. M. Flasar, ibid. 91, 112 (1991); J. I. Lunine and D. J. Stevenson, Nature 317, 238 (1985).
33. S. Engel, J. I. Lunine, W. K. Hartmann, Planet. Space Sci. 43, 1059 (1995).
34. R. D. Lorenz, ibid. 44, 1021 (1996).
35. J.I.L. and C.P.M. were supported through the NASA Planetary Atmospheres and Geology-Geophysics programs, and R.D.L. through the Cassini project.