NASA scientists think they can now tie dark streaks seen on the surface of Mars to periodic flows of liquid water.
For a long time, scientists have thought these streaks come from a salty brine that’s solid in the winter but melts in the springtime, streaming downhill. But since the streaks are only 5 meters wide at most, the satellites couldn’t get a clear enough look to analyze their composition.
Data from a NASA’s Mars Reconnaissance Orbiter (MRO) shows the features, which appear on slopes, to be associated with salt deposits.
Crucially, such salts could alter the freezing and vaporization points of water in Mars’s sparse air, keeping it in a fluid state long enough to move.
The study is published in today’s Nature Geoscience.
There are implications for the existence of life on the planet today, because any liquid water raises the possibility that microbes could also be present. And for future astronauts on Mars, the identification of water supplies near the surface would make it easier for them to “live off the land”.
Researchers have long wondered whether liquid water might occasionally flow across the surface today.
It is not a simple proposition, because the temperatures are usually well below zero Celsius and the atmospheric pressure is so low that any liquid H2O will rapidly boil.
The observation over the past 15 years of gullies and surface streaks that appear to change with the seasons has heightened the speculation.
Dr. Lujendra Ojha has now presented new data from the MRO that seems to solve the conundrum.
MRO has an instrument called Crism that can determine the chemistry of surface materials.
It has looked at four locations where dark streaks are seen to come and go during Martian summer months.
Crism finds these “recurring slope lineae” (RSL) to be covered with salts.
They are salts – magnesium perchlorate, chlorate and chloride – that can drop the freezing point of water by 80 degrees and its vaporization rate by a factor of 10.
The combination allows briny water to stay stable long enough to trickle down hillsides and crater walls.
Quite where the water is coming from to make the streaks is still unclear, however. The locations studied by MRO are equatorial, and any stored water in this region of Mars, perhaps in the form of ice, is thought to exist only at great depth.
One possibility is that the salts actually pull the water out of the atmosphere. The Curiosity rover has found some strong pointers to this mechanism. But again, it is not known whether there is a sufficient supply in the air to facilitate a decent flow.
Another theory is that local aquifers are breaking up to the surface, but this does not really fit with streaks that appear from the tops of peaks.
It is conceivable that streaks are being formed from different sources in different parts of Mars.
The findings strongly suggest that the brine hypothesis is correct—in which case, it would mean there’s liquid water on Mars, at least seasonally. That’s great news for scientists who still think life could be lurking on Mars.
The potential for life on Mars is still a long shot, but worth looking into, the authors write.
“The detection described here warrants further astrobiological characterization and exploration of these unique regions on Mars.”
NASA’s old Opportunity rover on Mars has just made what may be one of its most significant discoveries to date.
Nine-year-old Opportunity rover has identified rock laden with what scientists believe to be clay minerals.
Their presence is an indication that the rock, dubbed Esperance, has been altered at some point in the past through prolonged contact with water.
Opportunity has seen a clay-bearing outcrop before but scientists say this is by far the best example to date.
“It’s very rich,” said Steve Squyres, the rover’s principal investigator.
“We’ve been discovering evidence for water on Mars since we first landed back in 2004. What’s different here?
“If you look at all of the water-related discoveries that have been made by Opportunity, the vast majority of them point to water that was a very low pH – it was acid.
“We run around talking about water on Mars. In fact, what Opportunity has mostly discovered, or found evidence for, was sulphuric acid.
“Clay minerals only tend to form at a more neutral pH. This is water you could drink. This is water that was much more favorable for things like pre-biotic chemistry – the kind of chemistry that could lead to the origin of life.”
Opportunity Mars rover discovers Esperance rock with signs of water
Prof. Steve Squyres, who is affiliated to Cornell University, Ithaca, New York, said he was inclined to put Esperance in his personal top five discoveries made on Mars by Opportunity and her twin rover, Spirit, which stopped working in 2011.
The clays are aluminium-rich, possibly of the type montmorillonite. However, because Opportunity’s X-ray spectrometer can only discern the atomic elements in a rock, and not their mineralogical arrangement, no-one can say for sure.
Nonetheless, the mere occurrence of clays is further proof that the Red Planet was much warmer and wetter billions of years ago; a very different place to the cold, desiccated world it has become.
And these results complement nicely those of NASA’s newer rover Curiosity, which has also identified clays at its landing site almost half-way around the planet’s equator.
The old robot made its find at a location called Cape York, which is sited on the rim of a 22 km-wide crater known as Endurance.
Mission managers have now commanded it to start moving along the ridge to a destination dubbed Solander Point.
There is an expectation that Opportunity will find a deeper stack of rocks at the new location to follow up the Esperance water story.
“Maybe [we can] try to reconstruct the actual depositional environment of these materials and whether they were lacustrine – that is, formed by a lake – or fluvial (river) or an alluvial fan (network of streams), or whatever,” said deputy principal investigator Ray Arvidson, of Washington University, St Louis.
Opportunity is now operating well beyond its expected lifetime.
When it landed at Eagle Crater in January 2004, NASA hoped to get at least 90 working Martian days (sols) from the machine. Remarkably, it continues to roll beyond 3,300 sols.
It has an “arthritic” robotic arm, its solar panels are losing efficiency, and it drives backwards to save wear on its locomotion system.
Opportunity is also now having to contend with glitchy flash memory. But NASA is determined to keep pushing the vehicle for as long as possible.
“Remember, the rover continues in a very hostile environment on Mars,” said John Callas, NASA’s Opportunity project manager.
“The rover could have a catastrophic failure at any moment. So, each day is a gift.”
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