Titan Unveiled

By James Anderson

 
            When the Huygens probe landed on the surface of Titan on January 14, it revealed a world in some ways remarkably similar to Earth, yet at the same time totally alien.

Photographs show what appears to be a network of channels and rivers leading into lakes.  There are even “islands” visible in these lakes.  Though these rivers and lakes appear to be dry at the present time, there was probably a time when rain fell on Titan and reshaped its surface.  This rain was not water, but methane, which can condense to a liquid in the extreme cold of the outer solar system. 

            Images of Huygens’ landing site indicate that it rests in a dry riverbed.  Smooth, rounded rocks bear witness to the action of an eroding liquid.  But these rocks are not made of the familiar minerals we find on Earth.  Instead, they are composed mostly of dirty water ice.  At temperatures of –180 °C (–290 °F), water ice is solid rock, nothing like the slippery, easily melted substance we find on Earth.

            Life is unlikely to exist on this frigid world, as all known life depends on liquid water, which cannot exist in such low temperatures.  But some scientists have claimed that Titan is similar to the early Earth.  Its atmosphere, they suggest, provides an opportunity to study the chemistry that lead to the formation of life on Earth. [1]

This is based on the assumption that the early Earth’s atmosphere did not have any oxygen.  That is a natural assumption from an evolutionary perspective, as oxygen would prevent the formation of the organic compounds which are necessary for life.  But there is actually evidence that oxygen would have been present—which means life would not have evolved. [2]

Side view of Titan's atmos-
phere, hundreds of km. thick.
Colorized UV image;
NASA/JPL/Space Science
Institute

It is likely, then, that Earth’s atmosphere was never like Titan’s.  Studies of the origin of life are far from explaining the many difficulties, and the exploration of Titan is unlikely to make matters any easier. 

Origin of Life and Chemical Evolution

Cassini-Huygens

Titan Weather

Detailed Full-Disc View

South Polar Cloud Animation

The animation on the right is a combination of 45 images taken by the Cassini Orbiter spacecraft.  They show an almost complete rotation of Titan and deliver clear detail of the moon's surface. 
Courtesy NASA/JPL/Space Science Institute

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Article © 2005 James Anderson.  Used by permission.
(Top) Titan river channel mosaic and landing site image courtesy ESA/NASA/JPL/University of Arizona

[1] Chaisson, Eric and Steve McMillan.  Astronomy: A Beginner’s Guide to the Universe.  Fourth Edition.  Upper Saddle River, New Jersey: Pearson Education, Inc.  2004.  p. 218.