It was a search hundreds of years old. On Monday, NASA announced what so many have sought for so long – a groundbreaking discovery by the Mars Reconnaissance Orbiter (MRO) of definitive evidence of recent salt water flows on Mars. The discovery confirms long-held suspicions and mounting evidence from MRO and places Mars into a category of a planet that until now only had one occupant – planets with current water flow activity.
Mars Reconnaissance Orbiter’s storied history:
MRO, one of two missions considered as part of the 2003 Mars launch window opportunity, was designed to be a permanent orbiting presence at Mars with a suite of instruments performing detailed, round-the-clock, yearly observation of the Martian surface.
With an initial mission duration of two Earth years, one Martian year, from November 2006 to November 2008, MRO was launched from the Cape Canaveral Air Force Station, Florida, atop an Atlas V rocket on 12 August 2005.
After a seven and a half month journey from Earth, MRO arrived at Mars for orbital insertion operations on 10 March 2006.
A 27 minute engine burn slowed MRO from 2,900 to 1,900 m/s, allowing it to be captured by Mars’ gravity in a highly elliptical polar orbit with an initial orbital period of 35.5 hours.
MRO then spent the first five months of its tenure at Mars in an aerobraking orbit to continuously lower and circularize its orbit for shorter periods.
Aerobraking and orbit circularization maneuvers were completed on 30 August 2006 followed by two September firings of MRO’s thrusters to fine-tune its near-circular orbit to 250 x 316 km above the Martian surface with an orbital period of 112 minutes.
By 2009, radar measurements obtained from MRO allowed scientists to accurately measure the northern polar ice cap of Mars and determine its volume of water ice at 821,000 cubic km, approximately 30% of the Greenland ice sheet on Earth.
Furthermore in 2009, information from MRO led to the discovery that some craters on Mars had been recently excavated with relatively pure water ice.
Captured by the Compact Imaging Spectrometer onboard MRO, the new craters were found to have been formed by ice after it was exposed to the surface environments and sublimated away.
A total of five of these craters were identified in various locations around the planet via information from MRO.
Moreover, information gathered by MRO has suggested that features called Lobate Debris Aprons (LDAs) contain large amounts of water ice due to their convex topography and gentle slopes, suggesting flow away from the steep source cliff.
These LDAs were further shown to have surface lineation just as rock glaciers on Earth.
That, coupled by strong reflections from the top and base of the LDAs suggested – though it was never confirmed – that pure water ice made up part of the formation.
Additionally, MRO provided data triangulated between itself, the Mars Global Surveyor, and Mars Odyssey regarding widespread deposits of chloride minerals.
On Earth, places with chloride minerals have supported life in the past and have preserved traces of ancient life.
But MRO’s greatest find came on its 2,125th solar day of operation at Mars – 4 August 2011 – when NASA announced that MRO had detected what appeared to be evidence of flowing salty water on the surface of Mars.
The potential discovery was made when MRO photographed dark, finger-like features extending down the side of some Martian slopes.
The finger-like features were observed to have faded away in winter and returned the following spring – observations possible due to the nature of MRO’s constant observational campaigns.
In fact, it would be these exact finger-like structures and the study of additional data from MRO that would lead to today’s announcement of the confirmation that liquid salty water flows are indeed present on current-day Mars.
Water on Mars:
The new findings from 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, 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), have often 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.
“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,” said Lujendra Ojha, lead author of a report on these findings published Sept. 28 by Nature Geoscience.
“In either case, the detection of hydrated salts on these slopes means that water plays a vital role in the formation of these streaks.”
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.
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 where 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.
NASA’s Phoenix lander and Curiosity rover both found perchlorates 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.
“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 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. 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.
“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.”
While the historic nature of this discovery cannot be understated, the confirmed presence of present-day liquid flowing water on the surface of Mars continues to lend evidence to the hypothesis that Mars was once a habitable planet that could have harbored life.
Moreover, the discovery holds potentially significant implications for current-day life on Mars. For on Earth, where there’s liquid water, there’s life.
The presence of not only water ice at the Martian poles but flowing, briny water on other areas of the planet under certain conditions holds great significance for future human exploration and the use of in-situ resources that may be vital to any human exploration of Mars.
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