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Titan: Exploring the origins of life

By by Michelle / December 12, 2002


Our view of the solar system has changed drastically in the last few decades. Take moons, for instance. The word moon implies something small and insignificant, at least compared to a planet. But so many of the moons, especially those around the outer planets, are fascinating and complex worlds unto themselves. Many of the most dramatic environments we know of, as well as some of the best chances for life outside the Earth, exist on the moons of our planetary family.

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One of the most tantalizing moons is Titan, the largest moon of Saturn. Even among all the fascinating moons in the solar system, Titan is unique: it is the only moon that possesses a significant atmosphere. Not only does it have an atmosphere, but also layers and layers of orange, hazy clouds (the clouds were so thick that when the Voyager Spacecraft flew by in 1980, the surface was entirely concealed.) Titan's atmosphere is actually quite a bit denser than the Earth's, which is really saying something when you consider the low surface gravity on Titan. Most people don't think about the Earth's gravity holding down and compressing the gases of our atmosphere, but that's exactly what happens. The gravity on Titan's surface in only about one tenth of what you feel on Earth, but the air pressure is actually 60 percent greater than what you feel at sea level here. That's a lot of atmosphere!

Not that you could breathe Titan's air, though. The composition of Titan's atmosphere is not totally unlike Earth's; the air on both our worlds is mainly composed of nitrogen (78 percent of our air is nitrogen, compared to 90 percent on Titan). But unfortunately, Earth seems to be unique among all the planets and moons in having a significant amount of oxygen; Titan has practically none. There's also the problem of air temperature: even on the balmiest days, the temperature rarely gets much above 300 degrees below zero Fahrenheit.

Yet it's this extremely low temperature that may make Titan such an interesting place to visit. At these cryo-freezing levels, both methane (what we think of as natural gas) and ethane exist in liquid form. There may be puddles, lakes, or even oceans of liquid ethane and dissolved methane sloshing around on the surface. No one has directly observed any lakes or oceans yet, but the conditions on Titan heavily imply that such things could exist. You'll have to keep posted on that one.

How amazing it would be to stand on a frozen shore and watch waves of liquid ethane crash onto the beach. And yes, scientists are pretty sure that if such oceans exist, there would be waves and tides. Titan orbits fairly close to its parent planet, and Saturn is much more massive than the Earth. These two combined effects mean that tidal forces on Titan are over four hundred times stronger than what we feel on Earth.

Fortunately, that doesn't matter much because like our own moon, Titan has been tidally locked in its orbit around its planet. Even so, scientists believe waves exist. The elliptical shape of Titan's orbit changes its distance to Saturn over sixteen days, one "month" on Titan. These small changes are enough to generate a small, but noticeable tide of about ten feet. Saturn's gravity also generates tides in Titan's atmosphere (tidal winds! very cool), which keeps a constant wind-speed of a few miles per hour chopping up those liquid ethane oceans.

But frigid oceans and tidal weather patterns are not the only reasons Titan has gotten everyone so excited. For a long time now, scientists have been searching for environments outside the Earth that may support life, and Titan has loomed large on their list.