Astronomers see possibility of water on Mars - USA Today (blog)

An explanation for dark lines that appear on the steep slopes of Martian hills in the spring and summer could suggest some interesting possibilities for life, exobiologists say.

The lines might be briny water melting out of frozen, frosty slushes, researchers suggest in a paper in this week's edition of the journal Science.

The lines aren't large, just 1.5 to 15 foot wide channels that snake down steep hillsides in the middle latitudes of Mars' southern hemisphere. But astronomers say images from the Mars Reconnaissance Orbiter High Resolution Imaging Science Experiment "show them to appear and incrementally grow during warm seasons and fade in cold seasons," the paper says

The temperatures in those areas during the Martian spring and summers can reach between 10 and 80 degrees, could be enough to allow frozen water to thaw and dampen the rocks and sand around it.

The lines, which can be quite long, are between 1.5 and 15 feet across.vThe authors suggest three possibilities to explain them:

- water migration, which would require "ample pure water"

- geothermally heated water

- brines whose freezing point is depressed because of their salt concentration

Brines make the most sense, they say.

The presence of brines is the most realistic scenario for Mars, requiring modest quantities of water and no geothermal heat. Furthermore, the brine model exhibits a dependence of discharge on season and favors equator-facing slopes in the middle to high latitudes.

The presence of any kind of liquid water on a reoccurring basis on Mars could mean life, even if very primitive, could gain a foothold there.

The evidence presented is good, says Dirk Möhlmann, a physics professor who studies water in the solar system at the Planetary Research Institute in Berlin, Germany.

It's possible that these liquid, cold brines could play the same role that water plays on Earth, Möhlmann suggests. Organisms that make use of them would be limited to times when they were liquid enough to aid in life, meaning there would be "diurnal and seasonal periods of active life, if it would exist there, possibly repetitively followed by hibernation phases in between. Note that best conditions for liquefaction are on Mars given during night and morning hours. So, organisms may take up water during cold night and have their metabolic process over the warmer daytime hours."