Water May Flow On Mars

Scientists announced the best evidence yet that fluid streams down Martian slopes, according to the august 5 issue of science. While comparing images of mar's surface to detect subtle changes the team found dark streaks on steep inclines that seem to grow in size during warm season and fade in cold ones. "We soon realized they were different fro; slope streaks that had been observed before" says team member Lujendra Ojha of the university of Arizona in Tucson.

Called recurring slope linae (RSL); these marking extend downward from bedrock outcrops and other rocky areas. The features are about 1.6 to 16 feet (0.5 to 5 meters) wide and hundreds of feet long.

The discovery team, led by Alfred McEwen of the University of Arizona, found seven sites: some contain more than 1.000 RSLs, and all are in mid-southern latitudes on steeps slopes facing the equator. The team observed these features over multiple Martian seasons and found that they grow as the peak surface temperature tops 250 Kelvin's (-10° Fahrenheit). This isn't warm enough for pure liquid water to exist, but salts can lower water's melting point by 70 K (pure water's melting point is 273 K, or 32° F).salts also reduce the evaporation rate.

While McEwen and colleagues think briny water is the best guess of what causes these RSLs, they don't see the chemical signature of water in the features. They also aren't sure what the source of the liquid is.