The dark narrow streaks on Martian surface, discovered by NASA’s Mars Reconnaissance Orbiter, may have been formed by the flow of salty liquid water.
Norbert Schorghofer, a senior scientist at Planetary Science Institute, United States, explains that the dark streaks— called recurring slope lineae (RSL)—which appear seasonably are caused by briny water flowing for a few days annually. Seasonal flows on warm Martian slopes occur during the warmest months.
"The presence of liquid water on Mars' present-day surface therefore points to environment[s] that are more habitable than previously thought," study lead author Lujendra Ojha, of the Georgia Institute of Technology in Atlanta, told Space.com via email.
The team noted that liquid water is difficult to come by on the Red Planet, because ice rapidly dissipates into the atmosphere long before it reaches its melting point.
This is because the atmospheric pressure on Mars lies near the triple point pressure of water molecules (H2O), the minimum pressure necessary for liquid water to exist, they said.
"Mars has plenty of cold ice-rich regions and plenty of warm ice-free regions, but icy regions where the temperature rises above the melting point are a sweet spot that is nearly impossible to find," said
"That sweet spot is where liquid water would form," Schorghofer said.
In the study, published in The Astrophysical Journal, the researchers explained that a boulder sitting on the surface of Mars at mid-latitudes casts a shadow in winter.
The continually shadowed area behind the boulder is very cold, so cold that water ice accumulates in winter, they said.
When the Sun rises again in spring, the ice suddenly heats up.
In detailed model calculations, the researchers noted that the temperature rises from minus 128 degrees Celsius in the morning to minus 10 degrees Celsius at noon, a huge change over a quarter of a day.
Over such a short time, not all of the frost is lost to the atmosphere, according to the researchers.
Salt depresses the melting point of H2O, so on salt-rich ground, water ice will melt at minus 10 degrees Celsius, according to the researchers.
Brines, or salty water, will form until all of the ice has either turned to liquid or vapour, they said.
Next Mars year, the same process repeats, the researchers noted.
The shadowed areas behind the boulders are so cold in winter that not only water frost but also carbon dioxide ice builds up, they said.
(With inputs from PTI)