By GREG KLINE

The (Champaign) News-Gazette

URBANA, Ill. -- Gary Parker looks at images from Saturn's moon Titan and sees the Sangamon, the Illinois, the Wabash and other earthbound rivers.

Oh, there are differences to be sure. That stuff running in Titan's rivers is probably liquid methane, not water, for one thing. And if you plucked a stone from the shore to skip across the surface, you likely would be skipping ice, not rock.

Still, what appear to be rivers on Titan look a lot like rivers on Earth overall, wider maybe, a little deeper, not as steep but hardly as alien in appearance as you might think, said Parker, a University of Illinois civil and environmental engineering and geology professor.

Likewise Mars, where evidence shows that now-dry rivers carved Earthlike features in the surface.

"We know there were rivers on Mars," Parker said. "The rivers that we have seen ... show many Earthlike features."

The whole thing is a matter of physics, Parker said.

"The ultimate goal of science is to determine universal rules," he said. In his case, the rules governing what earthbound rivers do, how the results of that action look and why.

"Those same rules ought to hold for rivers of methane moving stones of ice on Titan," he added.

Truly understanding river dynamics at the physical level whether on the Earth's surface, undersea or on another planet has a practical side, said Parker, who's collected data on rivers from all over the world.

He's involved in a project aimed at regenerating the Mississippi Delta, for example, which could help mitigate hurricane damage, among other things.

Parker began applying what he knows to Saturn's largest moon after a book on the outer planets and their satellites piqued his interest.

Scientists studying Titan, the second-largest moon in the solar system and the only one with an atmosphere, already had indications that methane there, like water on Earth, could change from liquid to solid to gas depending on the weather, so to speak. There were indications of methane oceans, rain and snow as well. Why not rivers?

Parker said Titan's much lower gravity means rivers there should have a lower acceleration rate, leading to channel slopes somewhat wider, deeper and less steep.

He said some differences could have a significant impact, however. Take ice. Water is unusual in that, when it freezes, it floats. Methane ice, on the other hand, might sink, affecting flows on Titan.

That "would make rivers do things completely different than on Earth," Parker said.