June 23, 2010

Questions Remain About Water On Mars

It was ten years ago that NASA announced the discovery of photographs revealing gullies on the surface of Mars, something that suggested water might still be flowing on the surface of the planet.  

The breakthrough was followed by years of additional discoveries that pointed to the presence of water on the red planet.

But a decade later, there is still no conclusive proof that such water exists.  However, the search for evidence, along with the many revelations that have emerged along the way, has altered our perception of the planet.

"We are definitely on the path to exploring the habitability of Mars "” what it's been like in the past and even potentially now," said Michael Meyer, lead scientist for NASA's Mars Exploration Program, in an interview with Space.com.

Ten years ago, researchers reviewing data from NASA's Mars Global Surveyor spacecraft discovered what appeared to be gullies formed by flowing water, along with mud deposits and debris the flows may have left behind. At the time, scientists noticed that certain features of the gullies appeared so recent that they might still be in a formation stage.

NASA announced the findings in June 2000, and the research was published in that month's issue of the journal Science.

Evidence is plentiful that water once formed massive oceans in the distant past on Mars, sculpting valleys and other features that are clearly visible on the planet's surface today.

Yet, the potential presence of liquid water on the surface of Mars today is puzzling, because it could not exist there due to sub-zero temperatures and the sparse atmosphere. This conundrum has caused a contentious debate over the idea of whether or not water could flow on the surface.

Just last year, scientists suggested that semi-solid blobs of salty water observed on the legs of NASA's Phoenix Mars Lander were water, while others on the same team suggested the globs might have been frost instead.

However, there was no doubt that water ice was present near the site of the Phoenix lander that touched down in the Martian arctic.  Indeed, water ice has been discovered at the planet's poles inside craters and lying beneath the surface across large areas of the planet's mid-latitude regions. 

But scientists still question when water last existed on the surface of Mars.

"There's been no smoking gun evidence yet as to whether liquid water has been on the surface of Mars in the recent past," Meyer said.

One of the most significant challenges about proving whether or not water still flows on the Martian surface is that "where we have seen gullies also tends to be where we don't want to land spacecraft," he said.

"The hope is that orbiter missions can catch something in the act involving liquid water near the surface today," he explained.

"We do suspect there's liquid water in the subsurface "” it's just depends on how deep you have to go."

Europe's Mars Express spacecraft has been using ground-penetrating radar to search for unseen pockets of ice and liquid water. NASA's impressive Mars Reconnaissance Orbiter has also been searching for evidence of the history of water on Mars.

Despite the current debate, the past ten years have given scientists near certainty that there was once large quantities of water on Mars, and that there is much frozen water that remains hidden there today.

"We've gone from suspecting there was water on Mars once upon a time to deciding there definitely was water, and not only that there was water, but lots of water," said Meyer.

"Now with the Mars Reconnaissance Orbiter, we've found frozen water even at mid-latitudes, so the inventory of water on Mars is looking better and better as we learn more."

The importance of water on Mars derives from the critical importance of water to life here on Earth.

"How much water has been on Mars, how long we think it was there and how many places might have had it makes a difference in how habitable we think it might have been," Meyer said.

While scientists continue to search for water on Mars, "in many ways we are moving beyond specifically looking for water on Mars and more at what the consequences of water might be "” for example, minerals formed in the presence of water, particularly maybe organic matter, which might have preserved what went on in early Mars," Meyer told Space.com.

The entire effort is centered on determining whether or not life does, or ever did, exist on the planet.

"Currently we're holding landing site workshops for the Mars Science Laboratory, which is set to launch next year, for specific places to go to look at such minerals," he said.


Image Caption: This image taken by Mars Global Surveyor spans a region about 1,500 m (4,921 ft) across, showing gullies on the walls of Newton Basin in Sirenum Terra. Similar channels on Earth are formed by flowing water, but on Mars the temperature is normally too cold and the atmosphere too thin to sustain liquid water. Nevertheless, many scientists hypothesize that liquid groundwater can sometimes surface on Mars, erode gullies and channels, and pool at the bottom before freezing and evaporating. Credit: Malin Space Science Systems, MGS, JPL, NASA


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