Question

For astronomy class, please answer this question clearly, thank you .

Titan’s atmosphere contains a large amount of photosensitive methane. We know because of basic physics and chemistry that there must be a source of methane on Titan that replenishes the atmospheric methane.

a) Describe what astronomers thought might be occurring on Titan before the Cassini/Huygens mission.

b) Describe the findings of the Cassini/Huygens mission that either supported or disproved the original hypotheses.

Answer 1

Solution :

Part a :

Before Cassini/ Huygens mission, the astronomers had an abstract idea about Titan and its atmosphere. They were unaware of the chemical reactions taking place on the atmosphere of Titan. The determination of bulk constituents of Titan from Voyager's data was a herculean task. Titan was only known to be a vague, orange colored, mercury sized moon of Saturn. It is dark and cold place, but at the surface, the temperature reaches ~94 K due to greenhouse effect ( Just like Earth). Astronomers predicted the presence of dense Nitrogen, akin to the Earth's atmosphere, on Titan. In addition to it, they also came to a conclusion that it would rain methane on Titan. Because of the thick haze covering the moon, nothing more could be concluded before the Cassini- Huygens mission happened.

Part b:

Cassini/Huygens unraveled mysterious elements of Titan apart of answering the questions of astronomers. Initially, astronomers assumed that Titan had widespread surface hydrocarbon seas, but this mission confirmed the presence of seas localized to north pole. The rotational oscillation of Titan was in agreement with initially predicted model. Cassini's gravity measurements shed light on the liquid water and ammonia beneath it's surface which gave a hint of habitable conditions. Titan was found to have an arid region of hydrocarbon dunes ( like Earth has regions of silicates/sand) near its equator. The temperature profile of Titan resembled to that of the Earth's thermal structure. As in, Cassini documented that Titan exhibited exosphere, mesosphere, stratosphere and troposphere in addition to stratopause and tropopause. The data obtained from the lower atmosphere of Titan by Cassini was in accordance with the data obtained from Voyager. The primitive nebula model proposed comprised of two distinct deuterium reservoirs that co-existed before the formation of the solar system: the main one in gaseous hydrogen (HD) and the second smaller one in deuterated isotopes of CNO compounds (such as methane, ammonia and water) trapped in ices or clathrates or adsorbed on grains. Titan's atmosphere could possibly result from volatile degassing of grains emanating from the second reservoir and having accreted to form the satellite. Thus Cassini/ Huygens mission managed to unravel many hidden aspects of Titan which were earlier misinterpreted or not clearly understood.