Nov. 20 (UPI) -- New research undermines evidence used to suggest water still flows on present day Mars.
Water was once abundant on Mars. That water is not mostly gone, but some studies have suggested Martian slopes still host the occasional flow. However, new analysis of these flow signatures suggest the dark streaks are caused by moving grains and dust.
The narrow, dark lines along downward-sloping features on Mars' surface are known as Recurring Slope Lineae. Previous surveys of the lines suggest RSL expand slowly and fade after periods of inactivity. They're seasonal and become most apparent during Mars' warmer months.
The lines look similar to those formed by water running down a dirt embankment on Earth, leading some scientists to believe the lines are formed by liquid water flows.
But new HiRISE images suggest the lines are more likely formed by sand and dust grains moving downslope.
"We've thought of RSL as possible liquid water flows, but the slopes are more like what we expect for dry sand," Colin Dundas, scientist at the U.S. Geological Survey, said in a news release. "This new understanding of RSL supports other evidence that shows that Mars today is very dry."
Researchers determined that the RSL terminals are nearly identical to those of sand dune slopes. Additionally, scientists calculated that large amounts of water would need to be present to form RSL -- an unlikely reality.
If water was responsible for the lines, their length would correspond with the height of the slope from which they originated. But analysis of RSL showed the lines all terminate at the same slope, regardless of their length.
The slope at which the lines terminate is similar to the angle of repose for sand, the steepest angle at which sand can be piled without beginning to collapse.
Researchers shared their analysis in a paper published Monday in the journal Nature Geoscience.
Their findings conform with the popular hypothesis that Mars is mostly devoid of liquid water.