Na Marsu je tekoucí voda, což zároveň zvyšuje pravděpodobnost existence života na rudé planetě. Předpoklad, že na Marsu je přítomna voda i v tekoucím skupenství, dnes potvrdili vědci z NASA. Soudí tak z kanálů vytvořených na úbočích hor a sezónně proměnlivé přítomnosti minerálů soli.
New findings from NASA’s Mars Reconnaissance Orbiter (MRO) provide the strongest evidence yet that liquid water flows intermittently on present-day Mars.
Using an imaging spectrometer on MRO, researchers detected signatures of hydrated minerals on slopes where mysterious streaks are seen on the Red Planet. These darkish streaks appear to ebb and flow over time. They darken and appear to flow down steep slopes during warm seasons, and then fade in cooler seasons. They appear in several locations on Mars when temperatures are above minus 10 degrees Fahrenheit (minus 23 Celsius), and disappear at colder times.
“Our quest on Mars has been to ‘follow the water,’ in our search for life in the universe, and now we have convincing science that validates what we’ve long suspected,” said John Grunsfeld, astronaut and associate administrator of NASA’s Science Mission Directorate in Washington. “This is a significant development, as it appears to confirm that water — albeit briny — is flowing today on the surface of Mars.”
These downhill flows, known as recurring slope lineae (RSL), often have been described as possibly related to liquid water. The new findings of hydrated salts on the slopes point to what that relationship may be to these dark features. The hydrated salts would lower the freezing point of a liquid brine, just as salt on roads here on Earth causes ice and snow to melt more rapidly. Scientists say it’s likely a shallow subsurface flow, with enough water wicking to the surface to explain the darkening.
„We found the hydrated salts only when the seasonal features were widest, which suggests that either the dark streaks themselves or a process that forms them is the source of the hydration. In either case, the detection of hydrated salts on these slopes means that water plays a vital role in the formation of these streaks,“ said Lujendra Ojha of the Georgia Institute of Technology (Georgia Tech) in Atlanta, lead author of a report on these findings published Sept. 28 by Nature Geoscience.
Ojha first noticed these puzzling features as a University of Arizona undergraduate student in 2010, using images from the MRO’s High Resolution Imaging Science Experiment (HiRISE). HiRISE observations now have documented RSL at dozens of sites on Mars. The new study pairs HiRISE observations with mineral mapping by MRO’s Compact Reconnaissance Imaging Spectrometer for Mars (CRISM).
The spectrometer observations show signatures of hydrated salts at multiple RSL locations, but only when the dark features were relatively wide. When the researchers looked at the same locations and RSL weren’t as extensive, they detected no hydrated salt.
Ojha and his co-authors interpret the spectral signatures as caused by hydrated minerals called perchlorates. The hydrated salts most consistent with the chemical signatures are likely a mixture of magnesium perchlorate, magnesium chlorate and sodium perchlorate. Some perchlorates have been shown to keep liquids from freezing even when conditions are as cold as minus 94 degrees Fahrenheit (minus 70 Celsius). On Earth, naturally produced perchlorates are concentrated in deserts, and some types of perchlorates can be used as rocket propellant.
Perchlorates have previously been seen on Mars. NASA’s Phoenix lander and Curiosity rover both found them in the planet’s soil, and some scientists believe that the Viking missions in the 1970s measured signatures of these salts. However, this study of RSL detected perchlorates, now in hydrated form, in different areas than those explored by the landers. This also is the first time perchlorates have been identified from orbit.
MRO has been examining Mars since 2006 with its six science instruments.
„The ability of MRO to observe for multiple Mars years with a payload able to see the fine detail of these features has enabled findings such as these: first identifying the puzzling seasonal streaks and now making a big step towards explaining what they are,“ said Rich Zurek, MRO project scientist at NASA’s Jet Propulsion Laboratory (JPL) in Pasadena, California.
For Ojha, the new findings are more proof that the mysterious lines he first saw darkening Martian slopes five years ago are, indeed, present-day water.
„When most people talk about water on Mars, they’re usually talking about ancient water or frozen water,“ he said. „Now we know there’s more to the story. This is the first spectral detection that unambiguously supports our liquid water-formation hypotheses for RSL.“
The discovery is the latest of many breakthroughs by NASA’s Mars missions.
“It took multiple spacecraft over several years to solve this mystery, and now we know there is liquid water on the surface of this cold, desert planet,” said Michael Meyer, lead scientist for NASA’s Mars Exploration Program at the agency’s headquarters in Washington. “It seems that the more we study Mars, the more we learn how life could be supported and where there are resources to support life in the future.”
There are eight co-authors of the Nature Geoscience paper, including Mary Beth Wilhelm at NASA’s Ames Research Center in Moffett Field, California and Georgia Tech; CRISM Principal Investigator Scott Murchie of the Johns Hopkins University Applied Physics Laboratory in Laurel, Maryland; and HiRISE Principal Investigator Alfred McEwen of the University of Arizona Lunar and Planetary Laboratory in Tucson, Arizona. Others are at Georgia Tech, the Southwest Research Institute in Boulder, Colorado, and Laboratoire de Planétologie et Géodynamique in Nantes, France.
The agency’s Jet Propulsion Laboratory (JPL) in Pasadena, California manages the Mars Reconnaissance Orbiter Project for NASA’s Science Mission Directorate, Washington. Lockheed Martin built the orbiter and collaborates with JPL to operate it.
More information about NASA’s journey to Mars is available online at:
For more information about the Mars Reconnaissance Orbiter, visit:
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Water flows on Mars, before our very eyes (New Scientist)
Liquid water has flowed on the surface of Mars within the past five years, suggest images by the now lost Mars Global Surveyor (MGS). The results appear to boost the chances that Mars could harbour life.
In 1999, MGS spotted gullies carved on the sides of Martian slopes. Thousands of gullies have been imaged since then, most recently by the Mars Reconnaissance Orbiter (MRO) (see Stunning snaps from the best camera ever sent to Mars).
The gullies appear to have formed sometime in the past several hundred thousand years, since impact craters have not accumulated on top of them. But exactly how long ago material flowed through them has not been clear.
Now, new flows have appeared in two of the gullies monitored by MGS, showing that they have been active within the past several years. The research was led by Michael Malin of Malin Space Science Systems in San Diego, California, US. That company operates the Mars Orbiter Camera on MGS, which acquired the images.
One gully on a crater wall that was imaged in 2001 was found to have filled with light-coloured material when it was re-imaged in 2005. A similar new light-coloured deposit appears in a 2004 image of crater gullies previously imaged in 1999.
The researchers suggest the deposits were made by liquid water flowing out from beneath the surface. The researchers estimate that each flow would have involved 5 to 10 swimming pools’ worth of water.
It would have been similar to a flash flood in the desert, says team member Ken Edgett of Malin Space Science Systems. “If you were there and this thing was coming down the slope, you’d probably want to get out of the way,” he says.
Any liquid water exposed to Mars’s atmosphere would quickly freeze, but Malin’s team says even if the exterior of the flow rapidly freezes, water could continue flowing much farther inside this ice shell, developing into a thick mixture of ice and sediment that would eventually freeze completely.
In Mars’s thin atmosphere, ice left on the surface would quickly sublimate, changing from a solid to a gas, and disappear. But water vapour diffusing out from deeper in the mixture of ice and sediment could repeatedly coat the surface with frost, maintaining its light colour long enough for MGS to spot it, the researchers say.
Alternatively, salt deposited from salty water or sediment placed there by water flow may be responsible for the light colour.
MGS team member Phil Christensen of Arizona State University in Tempe, US, who was not involved in this study, says he is convinced that the gullies were formed by the action of liquid water.
“It says something is actively going on today in at least some of these gullies and one intriguing possibility is that water was released,” he told New Scientist.
“I think they make a pretty good case that these aren’t simply dust avalanches or some wind-related process,” he says. He adds that the sublimating carbon dioxide scenario is even less likely, because temperatures in the regions where the gullies are found – between 30° and 60° from the equator – are too high for the gas to get frozen in the first place.
Allan Treiman of the Lunar and Planetary Institute in Houston, Texas, US, agrees that something flowed recently to make the observed changes.
But he is not convinced that water was involved. “There is no direct evidence of water in the images – only that something flowed downhill. My money is on sand and dust, because there’s lots and lots of sand and dust on Mars.”
Streaks on slopes have been observed before and interpreted as the result of dust avalanches. But these appear to be a separate phenomenon from the new light-coloured gully deposits, the researchers say.
Newly formed dust streaks have been observed, but are always dark. The dust streaks are also usually observed in areas where the surface clearly has a thick coating that could be dust, unlike the two craters in question. And dust streaks have never been observed on the same slopes where gullies carve into the surface.
The formation of new gullies has been observed before also, but these were on the sides of sand dunes, and were more clearly related to avalanching sand (see Landslips, impacts and eroding ice revealed on Mars).
If the deposits are the result of liquid water flow, the source of the water is not clear. Malin’s team suggests it comes from underground aquifers, perhaps kept liquid at low temperatures with the help of high salt concentrations.
Christensen says it could result from the removal of dust from a hypothetical layer of snow, which would then melt when exposed to sunlight.
The SHARAD radar on MRO is potentially capable of detecting any underground pockets of water that the flows might have come from, Malin says. “We’re hopeful that as SHARAD flies of over these locations it may be able to detect these subsurface aquifers,” he says.
The new evidence that liquid water may flow on Mars today boosts the chances that life could be present, Christensen says. “I believe that we have found places on Mars where you could take terrestrial life forms that live on snow or in aquifers and put them there and they would survive,” he says.
Malin’s team also reports in the same study the formation on Mars of 20 new craters between 2 and 150 metres across since 1999, confirming the previously estimated rate of crater formation and reinforcing the view that crater-free areas of Mars must truly be young or recently modified.
The discovery may be one of the last from MGS, which went silent shortly before its 10th launch anniversary in early November, and has not been heard from since (see Europe joins hunt for missing Mars probe).
Journal reference: Science (vol 314, p 1573)
By David Shiga
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