NASA rover Opportunity finds signs Mars once had fresh water
Source: Reuters
(Reuters) - NASA's decade-old Mars rover, Opportunity, has found evidence that life-friendly fresh water once pooled on the red planet's surface, reinforcing similar discoveries made by newcomer Curiosity on the other side of the planet, scientists said on Thursday.
Opportunity, along with its now-defunct twin, Spirit, landed 10 years ago for concurrent 90-day missions to look for clues of the past existence of water.
Both rovers did so, confirming evidence collected by orbiting spacecraft that Mars, the planet believed to be most like Earth in the solar system, was not always the cold, dry desert that appears today.
In August 2012, Curiosity, equipped with an onboard chemistry lab, arrived for follow-up investigations to determine if Mars had other ingredients essential for supporting life.
Read more: http://www.reuters.com/article/2014/01/23/us-space-mars-idUSBREA0M24P20140123
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stay liquid. So they are speculating that liquid water formed, but that probably only occurs on some special days and/or with the help of salts. But I'm not aware of a direct sighting.
http://www.exploremars.org/water-is-flowing-on-mars-right-now
Since June 2000, many hypotheses have been discussed at scientific meetings, in the scientific journals and elsewhere. The original June 2000 hypothesis held that the fluid was liquid water (either pure, salty, acidic, etc.) that came to the surface where slopes intersected conduits of groundwater. Such slopes include crater walls, valley walls, hills, massifs and crater central peaks. Later investigators explored the possibility that rather than liquid groundwater, the source was ground ice, which, under some climate conditions, melted to produce liquid runoff. Still others noted that thick mantles covered a fraction of the gully-bearing slopes, suggesting that the mantles were ancient, dust-covered snow or ice packs that might melt at the base to make liquid water runoff. Water was not the only fluid considered by various colleagues; carbon dioxide can be fluid at some pressures and temperatures. Fluid carbon dioxide was also proposed as a candidate fluidizing agent. Even dry mass movement, or land sliding, of unconsolidated granular material can exhibit some fluid-like behavior. Such mass movements were considered as an explanation for the gullies.
http://www.nasa.gov/mission_pages/mars/images/pia09031.html
