Alfred McEwen: Possibility of flowing salty water on Mars
On August 4, 2011, NASA announced that the planet Mars might have flowing water – possibly salt water – on its surface during its spring and summer months. The data are not conclusive, but they are “suggestive,” according to researchers. EarthSky spoke with planetary geologist Alfred McEwen, principle investigator of the High Resolution Imaging Science Experiment on the NASA’s Mars Reconnaissance Orbiter. This instrument revealed the possibility of flowing water during the warmest months on Mars. He said:
What we found are very interesting current phenomenon, flows, on steep slopes that are very particular about when and where and how they form. And we think we can explain this with the flow of salty water. And we haven’t been able to come up with any plausible alternative explanation.
The evidence comes from satellite images combined with 3-D computer modeling. The images reveal flows that appear in the planet’s spring and summer on a steep slope inside a large Martian crater called Newton crater.
Thousands of dark, finger-like features have been seen to appear and extend down some Martian slopes during late spring through summer on the Red Planet. The features fade in winter, and return the following spring. A report about the recurring flows was published in the August 4, 2011 edition of the journal Science.
Repeated observations have tracked the seasonal changes in these recurring features on several steep slopes in the middle latitudes of Mars’ southern hemisphere.
McEwen said in a press release:
The best explanation for these observations so far is the flow of briny water.
He told EarthSky:
These flows, if it’s salty water, salty water can be very different from fresh water. It can be thicker, gooier stuff, depending on the salt concentrations. We don’t really know. And the flows may actually be debris flows with a little bit of water mixed with the overlying dirt….So it isn’t necessarily a stream of water. It could be more like moving debris flows.
Fresh-looking gullies suggest slope movements in geologically recent times, perhaps aided by water. Purported droplets of brine also appeared on struts of the Phoenix Mars lander. If further study of the recurring dark flows supports evidence of brines, these could be the first known Martian locations with liquid water.
Some aspects of the observations still puzzle researchers, but flows of liquid brine fit the features’ characteristics better than alternate hypotheses. Saltiness lowers the freezing temperature of water. Sites with active flows get warm enough, even in the shallow subsurface, to sustain liquid water that is about as salty as Earth’s oceans, while pure water would freeze at the observed temperatures. Mars Reconnaissance Orbiter Project Scientist Richard Zurek of NASA’s Jet Propulsion Laboratory said:
These dark lineations are different from other types of features on Martian slopes. Repeated observations show they extend ever farther downhill with time during the warm season.
Liquid water on the desert surface of the planet Mars is a holy grail among space scientists, because water is critical for life as we know it. The results announced today are the closest scientists have come to finding evidence of liquid water on the planet’s surface today.
The image above shows locations on Mars where salt or water – mostly in frozen form – has been detected in the past. Plus, the blue squares mark locations of the type of feature reported today (August 4, 2011). The blue coloration at the top and bottom of the map – corresponding to high latitudes north and south on Mars – indicates higher concentrations of water ice.
The white squares in the northern hemisphere mark locations of small fresh impact craters that exposed water ice close to the surface.
The red squares mark the locations of salt deposits that could have resulted from evaporation of salty water.
The recurring dark features on Mars related to today’s announcement (blue squares) are only about 0.5 to 5 yards or meters wide, with lengths up to hundreds of yards. Some of those locations display more than 1,000 individual flows. While gullies are abundant on cold, pole-facing slopes, these dark flows are on warmer, equator-facing slopes.
More research, said McEwen, is needed to verify whether the satellite images show water flow on Mars. And if there’s water, he said, there could be life. He added:
The most important thing to me is that we’re still discovering new things about Mars that are surprising. We have a lot to learn yet. It’s a big planet. It’s a complex world.
Bottom line: NASA announced on August 4, 2011 yet more evidence of liquid water on our neighboring planet Mars. The evidence is suggestive, but not conclusive, that there is salty water flowing on Mars today during the warm spring and summer months. Mars Reconnaissance Orbiter obtained the images with the High Resolution Imaging Science Experiment (HiRISE). The images show thousands of dark, finger-like features that appear and extend down some Martian slopes during late spring through summer on the Red Planet. The features fade in winter, and return the following spring.