Thanks to robotic probes that have orbited and landed on Mars, scientists have known for some time that water once flowed on the Red Planet. However NASA announced on February 10, 2014 that the Mars Reconnaissance Orbiter and Mars Odyssey have picked up indications that near surface water is flowing on Mars currently.
“NASA spacecraft orbiting Mars have returned clues for understanding seasonal features that are the strongest indication of possible liquid water that may exist today on the Red Planet.
“The features are dark, finger-like markings that advance down some Martian slopes when temperatures rise. The new clues include corresponding seasonal changes in iron minerals on the same slopes and a survey of ground temperatures and other traits at active sites. These support a suggestion that brines with an iron-mineral antifreeze, such as ferric sulfate, may flow seasonally, though there are still other possible explanations.
“Researchers call these dark flows ‘recurring slope lineae.’ As a result, RSL has become one of the hottest acronyms at meetings of Mars scientists.”
Thus far none of the instruments being carried on space probes orbiting Mars has picked up water flow happening in real time. But the changes in the Martian landscape suggest water.
“One possible explanation for these changes is a sorting of grain sizes, such as removal of fine dust from the surface, which could result from either a wet process or dry one. Two other possible explanations are an increase in the more-oxidized (ferric) component of the minerals, or an overall darkening due to moisture. Either of these would point to water, even though no water was directly detected. The spectral observations might miss the presence of water, because the dark flows are much narrower than the area of ground sampled with each CRISM reading. Also, the orbital observations have been made only in afternoons and could miss morning moisture.
“The leading hypothesis for these features is the flow of near-surface water, kept liquid by salts depressing the freezing point of pure water.”
The possibility of near surface water on Mars has obvious implications, not only for the understanding of the Red Planet’s geology, but for the possibility of microbial life near its surface.