The streaks, technically dubbed Recurring Slope Lineae (RSL), are mostly found on rocky slopes in the dark regions of Mars. Scientists thought that maybe the warm summers allowed this salty water to flow.
Speaking about this research, US Geological Survey's Colin Dundas explains, "We've thought of RSL [recurring slope lineae] as possible liquid water flows, but the slopes are more like what we expect for dry sand".
The appearance and growth of these features resemble seeping liquid water, but how they form remains unclear, and this research demonstrated that the RSL flows seen by HiRISE are likely moving granular material like sand and dust. "This new understanding of RSL supports other evidence that shows that Mars today is very dry", said Dundas, lead author of the study published in the journal Nature Geoscience.
Although the fact that the RSL come and go with Martian seasons was originally attributed to the potential involvement of liquid water, high-res images captured by the Mars Reconnaissance Orbiter found evidence that they are caused by the movement of sand and dust.
An Atlas Centaur Rocket launch of Surveyor 1 | NASA | Wikimedia
Monday's news throws cold water on 2015 research that indicated these recurring slope lines were signs of water now on Mars.
These features have evoked fascination and controversy since their 2011 discovery, as possible markers for unexpected liquid water or brine on an otherwise dry planet. Each RSL ends in slopes which had "angle of response" similar to sand dunes on Mars and Earth. RSL served as compelling evidence of water on Mars. Liquid water would have readily extended to less steep slopes. It supports earlier theories that surface of modern Mars which had been exposed to cold, thin atmosphere, lacks flowing water. Dundas and coauthors examined 151 RSL features at 10 sites.
The NASA and other space agencies including private aerospace companies like SpaceX and Lockheed Martin have planned for their manned Mars mission from 2024.
"RSL probably form by some mechanism that is unique to the environment of Mars", McEwen says, "so they represent an opportunity to learn about how Mars behaves, which is important for future surface exploration". "There may be a small amount of liquid water involved. but this is pointing to a relatively dry mechanism".