Several photographs taken by NASA’s Phoenix Mars spacecraft show what look like water droplets clinging to one of its landing struts.

Some of the scientists working on the mission are asserting that that is exactly what they were. They contend that there are pockets of liquid water just under the Martian surface even though the temperatures in the northern plains never warmed above minus 15 degrees Fahrenheit during the six months of Phoenix’s operations last year.

The scientists believe that salts may have lowered the freezing temperature of the Martian water droplets to perhaps minus 90 degrees, or more than 120 degrees colder than the usual freezing temperature of 32 degrees for pure water.

Nilton O. Renno, a professor of atmospheric, oceanic and space sciences at the University of Michigan who proposed the hypothesis, was careful to say, “This is not a proof.”