Riding the rapids on Mars.

Come one, come all, on a grand tour of a major Martian waterway! Ride the rapids in Maja Canyon, spend lazy days fishing in the lakes of Lunae Planum and Xanthe Terra. Why not take a relaxing swim in the waters of western Chryse Planitia?

Such a scenario might not have seemed farfetched during a brief period several billion years ago -- an era, some researchers believe, when water carved the now-dry canyons and channels that scar the Martian surface. To understand the nature of these proposed ancient waterways, Rene A. De Hon and Eric A. Pani of Northeast Louisiana University in Monroe focused on Maja Valles, a system of canyons and channels some 1,600 kilometers long.

The researchers used standard fluid-flow equations, accounting for the region's sloped and Martian gravity, to calculate how long it would take water collecting at Juvantae Chasm--an uphill canyon -- to reach the Chryse Planitia basin, where it emptied. Nowadays, notes De Hon, such a journey would span a mere 44 hours, thanks to the direct path apparently carved by the ancient flow. But the initial rush of water would have taken a far more circuitous and time-consuming route to its final destination. Water would have temporarily collected in ponds, craters and depressions along the way until it spilled over onto adjacent regions.

De Hon and Pani calculate it would have taken some 430 Earth days for 62,000 cubic kilometers of water--the minimum amount believed held by the Juvantae Chasm canyon--to move through Maja Valles. Such a time scale appears long enough to have significantly eroded the Martian surface, they say.