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Images taken of the Phoenix Lander's leg on mission days 8, 31, and 44 show what scientists believe to be droplets of saline mud containing liquid water. Scientists believe that perchlorates in the soil act as antifreeze, keeping the water liquid. If so, the images would mark the first discovery of liquid water on Mars.  (Source: NASA/JPL-Caltech//University of Arizona/Max Planck Institute )
New photographs provide perhaps the most compelling evidence to date that there is liquid water on Mars

Mars has been the subject of intense interest of late.  Recent discoveries have shown the Martian atmosphere to contain methane, which comes primarily from biological sources, indicating that perhaps the planet once held life.  Further images of Martian glaciers provided more evidence that liquid water and ice may be flowing on the planet.

Now perhaps the most compelling photographic evidence to date of liquid water on Mars has been taken by the Phoenix Lander.  The Phoenix Lander is a NASA probe launched in 2007, which touched down early last year and has since been tasked with searching for signs of life on the planet.

The new photos were "self portraits" of the lander's leg.  What appears to be liquid droplets form on the leg and in time lapse images appear to glide across the surface, occasionally merging like water droplets. 

Phoenix co-investigator Nilton Renno of the University of Michigan has released a paper, which states that the droplets appear to be saline mud, containing water.  He believes the mud splashed up onto the lander when it touched down.  He says that the local sediments contain perchlorates, salts which can essentially act as antifreeze, potentially explaining how water could be staying liquid in the frigid Martian arctic region.

Other instruments on the Phoenix Lander failed to show signs of water in the local soil.  Furthermore, the pictures are relatively low resolution.  However, Professor Renno believes the droplet behavior points conclusively to water.  He states, "As it cooled down toward the end of the mission and we're seeing the formation of frost everywhere, the drops almost disappear.  This is consistent with [liquid] drops freezing and losing water to the atmosphere as it gets colder."

He cites features of one of the largest droplets, 0.4 inch (a centimeter) wide, which was imaged dripping down the leg, as further evidence.  The drop darkens before it drips, which is consistent with water, which is less reflective in its liquid form.  He describes, "Before it drips it becomes dark, and that's consistent with ice melting."

Nicholas Tosca, a geochemist at Harvard University, not involved with the study, spoke with National Geographic and said that the perchlorates found in the soil could indeed allow water in the area.  He says that perchlorate-containing droplets could stay liquid until -94 degrees Fahrenheit (-70 degrees Celsius), around the coldest temperature experienced by the lander at the time the images were taken.

He said that the strongly fluctuating polar temperatures would likely lead to cycles of freezing and melting.  This is consistent with Professor Renno's belief that the droplets liquefied during the day and froze at night.

Professor Tosca says the new findings are pretty strong evidence of liquid water on Mars, which would make the prospects of human inhabitation much more promising.  However, he says that the evidence does not provide any further support to theories about life on Mars due to the toxic nature of the perchlorate compounds in the soil.  He states, "If you make the case that life could have started on Mars and could be hiding out somewhere it's not likely to be in this cold, salty water."





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