Dark, narrow streaks on Martian slopes such as these at Hale Crater are believed to be formed by seasonal flow of water.  The streaks are roughly the length of a football field. Photo courtesy of: NASA/JPL-Caltech/Univ. of Arizona.

Scientists reported this morning that there is compelling evidence that liquid water exists on the surface of present-day Mars. The announcement was made based on new findings from NASA’s Mars Reconnaissance Orbiter (MRO) .Using an imaging spectrometer on MRO, researchers detected signatures of hydrated minerals on slopes where streaks are seen on the planet. These darkish streaks appear to ebb and flow over time, darkening and appearing to flow down steep slopes during warm seasons, and then fading in cooler seasons. They appear in several locations on Mars when temperatures are above minus 10 degrees Fahrenheit (minus 23 Celsius), and disappear at colder times.

In a paper published in the journal Nature Geoscience, Dr.Alfred S. McEwen, a professor of planetary geology at the University of Arizona and the principal investigator of images from a high-resolution camera on NASA’s MRO, and his colleagues identified salts of a type known as perchlorates in readings from orbit. The new findings of hydrated salts on the slopes point to what that relationship may be to these dark features. The hydrated salts would lower the freezing point of a liquid brine, just as salt on roads here on Earth causes ice and snow to melt more rapidly. Some perchlorates have been shown to keep liquids from freezing even when conditions are as cold as minus 94 degrees Fahrenheit (minus 70 Celsius).

NASA’s approach to searching for life in the universe has been to "follow the water". In the past when water on Mars has been discussed it was usually in the context of ancient water or frozen water. Today’s announcement shows there is more to the story as some sort of briny water appears to be flowing on the surface of the Red Planet.