Lakes, ridges, faults? A map of Titan emerges.

By , Staff writer of The Christian Science Monitor

Early snapshots of Titan, the enigmatic moon of Saturn, show it may be dimpled with huge lakes.

Its surface also seems to be etched with cracks or ridges - similar in signature to pressure ridges found in ice flows at the Earth's polar caps.

These features, as much as 650 feet wide, could be lava flows or evidence of surface faults that scientists have seen on another inhabitant of the solar system.

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"We've seen similar features in radar maps of Venus," says Charles Elachi, director of NASA's Jet Propulsion Laboratory in Pasadena and leader of the Cassini radar mapping team.

As the first data comes in from the space probe's historic flyby of Titan this week, scientists are trying to piece together what it all means.

Thursday, the spacecraft's radar team unveiled its initial map, yielding the first tentative evidence of lakes on the moon's surface - presumably filled with liquid hydrocarbons.

The results this week bode well for collecting data in the future, says Dr. Elachi. On subsequent flybys, the radar maps will cover the same territory as other sensors, allowing scientists to combine the results in ways that will help unlock the secrets of a solar system object thought to resemble Earth in many ways - long before life emerged.

The radar and other results are the latest in a stream of observations that are keeping Cassini scientists burning the midnight oil trying to decipher what they are seeing.

In analyzing images Cassini is beaming back, for example, bright regions on the surface appear to reflect some 20 percent more light than the dark regions.

Yet the way that light is reflected changes very little with wavelength from light patch to dark patch. This may suggest that that the surface composition between regions may be more uniform than visual images imply. Or it could mean that the surface may be coated with common compounds that mask the true composition of the layers underneath, further complicating efforts to measure their properties.

Robert Brown, a planetary scientist at the University of Arizona in Tucson and team leader for the spacecraft's visual and infrared mapping spectrometer, also notes that the dark areas - initially thought to be water ice when Cassini imaged Titan at a greater distance when it first arrived at Saturn in July - now show no evidence of water ice.

The atmosphere also is presenting puzzles. Measurements taken of atmospheric chemicals suggest that over geological time scales, Titan has lost up to 75 percent of its original atmosphere. Instruments also detected several surprisingly heavy carbon-based molecules at much higher altitudes than on other solar-system bodies. Typically, gravity keeps these heavyweights closer to the surface.

"Titan's atmosphere is well mixed" with altitude, and "that's the real surprise" for atmospheric chemists. The observation and follow-up measurements may hold clues to the evolution of Earth's atmosphere, says Hunter Waite, an atmospheric scientist at the University of Michigan who heads a team using Cassini's ion and neutral mass spectrometer.

Jonathan Lunine, a planetary scientist at the University of Arizona, notes that these heavier molecules likely are forming where they are, under the energetic influence of ultraviolet radiation from the sun.

Some discoveries have as much to with Cassini's capabilities than with Titan itself.

Brown notes that the spectrometer his team uses was never designed to build geological maps of the surface.

At the time, no one had discovered that the moon's haze was transparent at a handful of wavelengths of light. By clever use of the camera's 352 filters, the team has found it can build images showing terrain. That should allow scientists to begin matching surface composition with geological features more quickly, without having to await future flybys for radar images of the same locations.

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