Salty liquid water on Mars?

At yesterday’s NASA press conference, new evidence was presented for possible liquid water on Mars now, not just ice, which is widespread, and not just water from millions or billions of years ago. This has been discussed before as a distinct possibility, although this time the scientists involved seem more confident about this conclusion.

Streaks in Newton crater. Credit: NASA/JPL-Caltech/Univ. of Arizona

The new findings come from the Mars Reconnaissance Orbiter and its high-resolution camera system, HiRISE – long, narrow dark streaks emanating from bedrock on the rims of craters such as Newton crater or other slopes, in the mid-latitude regions of the southern hemisphere. They appear on slopes facing north toward the equator, during the Martian spring/summer, then fade and stop during the winter. Some locations have more than 1,000 individual flows. Their appearance, location and behaviour suggest liquid salty (briny) water as the most likely cause according to the scientists. The temperatures are too warm for carbon dioxide frost, but suitable for water during these relatively short periods. Salty water, or brines, would be be a better fit than pure liquid water, due to temperature fluctuations, but still water nonetheless.

Other dark streaks have been seen previously, but they don’t share the same characteristics as these ones, according to the scientists. So could there be different causes for different types of streaks? One problem that has caused skepticsm is the fact that the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) on MRO has so far not been able to definitively detect traces of water in the streak areas. According to Alfred McEwen, principal investigator for HiRISE, the relatively small amounts of water may dry/sublimate too quickly (which any type of water would do in the thin atmosphere regardless of temperature) or, as mentioned in the press conference, CRISM can’t resolve the streaks clearly enough with the resolution available, so confirming them would require subsequent observations and tests. Given the seasonal nature only during times of warmer temperatures, it seems clear that some kind of liquid or gas is involved, as opposed to dry landslides or dust devils as has been seem many times before in other locations. But is it water? Only further study will answer that question.

See all the HiRISE animated gif images here, the Science magazine article here and the Science magazine abstract here.