Not good news for Mars life. From ScienceDaily:
Dark features previously proposed as evidence for significant liquid water flowing on Mars have now been identified as granular flows, where sand and dust move rather than liquid water, according to a new article. These findings indicate that present-day Mars may not have a significant volume of liquid water. The water-restricted conditions that exist on Mars would make it difficult for Earth-like life to exist near the surface.
Scientists from the USGS, the University of Arizona, Durham University (England) and the Planetary Science Institute analyzed narrow, down-slope trending surface features on Mars that are darker than their surroundings, called Recurring Slope Lineae, or RSL. These RSL features grow incrementally, fade when inactive and recur annually during the warmest time of year on Mars. RSL are mostly found on steep rocky slopes in dark regions of Mars, such as the southern mid-latitudes, Valles Marineris near the equator, and in Acidalia Planitia on the northern plains. 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.
“We’ve thought of RSL as possible liquid water flows, but the slopes are more like what we expect for dry sand,” said USGS scientist and lead author Colin Dundas. “This new understanding of RSL supports other evidence that shows that Mars today is very dry.” Paper. (paywall) – Colin M. Dundas, Alfred S. McEwen, Matthew Chojnacki, Moses P. Milazzo, Shane Byrne, Jim N. McElwaine, Anna Urso. Granular flows at recurring slope lineae on Mars indicate a limited role for liquid water. Nature Geoscience, 2017; DOI: 10.1038/s41561-017-0012-5 More.
Mars is so close to Earth that it benefits from some features that enable life on Earth. Dashed hopes for Mars probably reduce the chances for similar exoplanets in galactic habitable zones.
See also: Was evidence for liquid water on Mars really discovered last year? Doubts surface.
New focus on deciding where to look “Become the microbe”?
Ancient water on Mars, not to be confused with the present day: