Strange globs seen on the landing strut of the Phoenix Mars lander could be the first proof that modern Mars hosts liquid water, a new paper reports.
Images from the robotic craft show what appear to be liquid droplets growing, merging, and dripping on the lander's leg over the course of a Martian month.
Phoenix landed near Mars's north pole last May, and several "self portraits" taken to assess the craft's health show material spattered on the legs.
This substance is probably saline mud that splashed up as the craft landed, study leader and Phoenix co-investigator Nilton Renno of the University of Michigan told National Geographic News.
Salt in the mud then absorbed water vapor from the atmosphere, forming the watery drops, Renno said.
The water can stay liquid even in the frigid Martian arctic because it contains a high amount of perchlorates, a salt "with properties like the antifreeze used to melt snow here in Michigan," said Renno, who will present the work next month at the 40th Lunar and Planetary Science Conference.
Finding liquid water under these conditions carries possible implications for Mars's habitability, the scientists say.
Dripping And Shrinkage
Renno admits that the images showing droplets are not high enough resolution to examine small details.
He also notes that instruments on board Phoenix meant to look for liquid water near the surface didn't find anything.
But he and his team are convinced that what they are seeing matches the behavior of liquid water.
"As it cooled down toward the end of the mission and we're seeing the formation of frost everywhere, the drops almost disappear," he said.
"This is consistent with drops freezing and losing water to the atmosphere as it gets colder."
What's more, the images suggest one of the largest globs started to drip down the lander's leg when it got bigger than about 0.4 inch (a centimeter) wide.
"Before it drips it becomes dark, and that's consistent with ice melting," said Renno, referring to the fact that ice is more reflective than liquid water.
It's certainly possible that liquid water could exist at least fleetingly on the Martian surface, said Nicholas Tosca, a geochemist at Harvard University who was not involved in the study.
With perchlorate present, Tosca agrees Mars could support liquid water even down to -94 degrees Fahrenheit (-70 degrees Celsius)â€”close to the lowest possible temperature around the lander's legs at the time the images were taken.
But daily temperatures fluctuate greatly on Mars, so even very salty water would probably go through cycles of freezing and melting. Liquids therefore wouldn't be present for very long periods of time, he said.
Study leader Renno thinks that the drops seen on Phoenix were liquid during the warmest part of the day but partially froze at night.
Overall, Tosca said, the paper makes a plausible case for liquid water on Mars, "but the nature of the water â€¦ doesn't bode well for life."
(Read more about Tosca's findings that water on early Mars would have been too toxic for life.)
Even if a layer of liquid does persist deep under Mars's surface, it wouldn't be very hospitable, he said.
"If you make the case that life could have started on Mars and could be hiding out somewhere," Tosca said, "it's not likely to be in this cold, salty water."