3. The invisible buffer zone with space - atmospheres, magnetospheres and the solar wind

Titan - a satellite with a substantial atmosphere

Saturn's largest moon, Titan, is the only satellite with a substantial atmosphere. Detailed investigations with instruments aboard Voyager 1 in 1980 showed that the dominant gas surrounding Titan is molecular nitrogen, N2, at 82 to 99 percent, similar to Earth (71 percent). In fact, the satellite is enveloped by about 10 times more nitrogen then we are, yielding a surface pressure 1.5 times greater than the sea-level pressure of Earth's atmosphere. The surface temperature on Titan is 94 degrees kelvin, as expected for a body so far from the Sun.

The spectrometers on Voyager 1 showed that the next-most abundant gas enveloping Titan is methane, CH4, with an abundance between 1 and 6 percent. Methane molecules rise up to high levels in Titan's atmosphere, where they are broken apart by ultraviolet sunlight and electrons coming from Saturn's magnetic environment. These molecular fragments recombine to form heavier hydrocarbon molecules such as ethane, C2H6, and familiar gases like acetylene, C2H2, propane, C2H8, and hydrogen cyanide, HCN.

It doesn't rain water on Titan, but it could rain fuel, in large drops that fall like snow. Given the known atmospheric composition and the temperatures, scientists speculate that thin clouds of methane ice crystals may form in the lower atmosphere. Ethane and propane can rain all the way down to the surface, forming seas, lakes and ponds. The patchy reservoirs of liquid hydrocarbons could be driving the weather cycle on Titan, with towering clouds of methane and a rainy drizzle of ethane.

Fig. .. 

We are not completely certain that there are any liquid seas on Titan, for we cannot see through its smog. The Voyager 1 cameras showed that an opaque haze completely enshrouds the satellite. The smog is unimaginably worse than a bad day in Los Angeles or Mexico City. Compared with any urban smog on Earth, there are relatively few smog particles per unit volume of Titan's atmosphere, but the haze extends to an altitude of about 200 thousand meters. This makes the smog thick enough to completely hide Titan's surface from view.

When the Cassini/Huygens spacecraft arrives at Saturn in mid-2004, it is expected to tell us what lies beneath Titan's obscuring veil of orange smog.

The planets are inside the expanding Sun

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Copyright 2010, Professor Kenneth R. Lang, Tufts University