New NASA Photos Point to Water on Mars

New clues are emerging about the mysterious streaks that appear on Mars' surface during warm weather, though scientists still can't say for sure that they're caused by flowing water.

The marks, known as recurring slope lineae (RSL), snake down some crater walls and other inclines when the mercury rises on the Red Planet. New research finds seasonal changes in iron minerals at RSL sites, suggesting that brines containing an iron antifreeze may flow there from time to time — but direct evidence of water remains elusive.

"We still don't have a smoking gun for existence of water in RSL, although we're not sure how this process would take place without water," Lujendra Ojha, a graduate student at Georgia Tech in Atlanta, lead author of two recent RSL studies, said in a statement. (Ojha discovered the RSL in 2011, while an undergraduate at the University of Arizona.)