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Forum:	Satellites - Robotic Probes
Topic:	Cassini-Huygens at Saturn: Questions, comments

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Your Reply: HTML is ON UBB Code is ON Smilies Legend	[QUOTE]Originally posted by Robert Pearlman: [B]Clarke was not so much lucky as he was well read (I assume). From SpaceDaily: [URL=http://www.spacedaily.com/news/early-sol-00e.html]Titan: A Primordial Earth In Our Solar System[/URL] September 22, 2000 <BLOCKQUOTE>[i]About the time Percival Lowell was proposing canals on Mars, the Catalan astronomer José Comas Solé, inferred the presence of an atmosphere on Titan. Solé reported that he observed that Titan was darker at its limb than it was at its center. He suggested that the mechanism for this was sunlight reflected toward the Earth by Titan's limb must pass through more of Titan's atmosphere than sunlight reflected by the center. Solés observations led Sir James Jeans to include Titan and giant moons of Jupiter in his theoretical study of the escape of atmospheres from the bodies of the solar system. Jeans hypothesized that even though the gravity on Titan was weak compared to the Earth. Titan nevertheless probably retained an atmosphere due to its low temperature. This lead to the prediction that the temperature of Titan must be between 60 and 100 Kelvin (273 K = 0oC), which would imply that a gaseous substance whose molecular weight is 16 or more should not have escaped from Titan over the history of the solar system. (Molecular hydrogen (H2) has a molecular weight of two; molecular oxygen (O2) has a molecular weight of 32]. Several substances satisfy Jean's limit on weight. These include argon, neon, molecular nitrogen (N2) and methane (CH4). In 1944 the legendary planetary scientist Gerald P. Kuiper, of the University of Chicago, identified methane in the spectrum of Titan -- the first strong evidence that Titan had an atmosphere. Subsequent observations by radar, telescopes and laboratory modeling painted varied pictures of Titan. For example, based upon previous work, John J. Caldwell of Princeton University, suggested that the atmosphere of Titan was 90% methane with a surface pressure of 20 millibars (1000 millibars is roughly the atmospheric pressure at sea level on the Earth) and a surface temperature of 86 K. Alternatively, based upon radio measurements, Donald M. Hunten of the University of Arizona proposed that Titan could have an atmosphere of molecular hydrogen at 20 bars and a surface temperature of 200 K. A middle ground was reached when Walter J. Jaffe and Tobias Owen observed Titan with the Very Large Array of radio telescopes situated in New Mexico. They found that Titan had a surface temperature of 87 K and that it could have a significant atmosphere with the caveat that nitrogen provided no more than two bars.[/i]</BLOCKQUOTE>[/B][/QUOTE]
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