The quest to confirm the existence of liquids on Mars has been ongoing for decades; it was known to host water billions of years ago and water is has been found to exist there in the form of ice, but the latest images from NASA's Mars Reconnaissance Orbiter (MRO) indicate that water may not only be present, but running down the Martian hills.
Newly released photographs from a variety of different locations across the southern latitudes of the Red Planet show dark streaks, known as ”recurring slope lineae” or RSL, that appear to course down inclines in the same manner as flowing liquid.
“The flow of water, even briny water, anywhere on Mars today would be a major discovery, impacting our understanding of present climate change on Mars and possibly indicating potential habitats for life near the surface on modern Mars,” Mars Reconnaissance Orbiter Project Scientist Richard Zurek said in the release.
Chemical evidence reveals that the streaks become more prominent during the Martian warm season, and recede as temperatures plummet, in much the same way as water levels might fluctuate in response to changes in temperature.
"Normally when you come up with something new in science, there's always a controversy" said Lujendra Ojha, a graduate student at the Georgia Institute of Technology in Atlanta and the lead author of the paper reporting the new results in the journal Geophysical Research Letters. Ojha said of the dark streaks: "no one has come out with a hypothesis that can explain these features without water. It's a very hard thing to explain without water."
In a study published in the journal Science in 2011, a team led by Lujendra Ojha revealed evidence based on data from the HiRISE camera aboard NASA's Mars Reconnaissance Orbiter that indicated the dark streaks were possible saltwater flows on Mars. It was originally thought that these RSIs could be attributed to landslides of thawing ice or accumulated rocks and sediment, but there is a distinct possibility that they show the release of water breaking through the surface and flowing down the slopes.
Whilst the presence of water has yet to be determined, evidence obtained from MRO's Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) has shown iron residues on the slopes where RSIs appear. CRISM works by assessing the way that different substances absorb light at distinct wavelengths, and Ojha's team found light absorption characteristics that were consistent with iron-containing substances. This could indicate that the water could contain an iron sulfate mixture - ferric sulfate - that acts as a form of "anti-freeze" preventing the water from freezing in the intensely cold Martian temperatures.
The light absorption readings fluctuated according to the seasons, said Ojha:
“Just like the RSL themselves, the strength of the spectral signatures varies according to the seasons. They’re stronger when it’s warmer and less significant when it’s colder,” he explained. "Something in these areas is actually causing the spectroscopic signature to fluctuate as well,"
He believes that water provides the best explanation for this, with flowing water being released from underground, and then evaporating during the course of the Martian day leaving only the residue behind. Other non-liquid causes are possible, however, such as variations in the Martian atmosphere the accumulation of particles.
"We still don't have a smoking gun for existence of water in RSL, although we're not sure how this process would take place without water," Ojha said in a statement from NASA.
The potential for "Life on Mars" increases with every new discovery. If underground water sources do exist on Mars, then what else could be lurking beneath the surface of the Red Planet?
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