NASA | JPL-Caltech | Mars Reconnaissance Orbiter | 2016 July 07
[img3="Blue dots on this map indicate sites of recurring slope lineae (RSL) in part of the Valles Marineris canyon network. RSL are seasonal dark streaks that may be indicators of liquid water. The area mapped here has the highest density of known RSL on Mars. Image Credit: NASA/JPL-Caltech/Univ. of Arizona"]http://photojournal.jpl.nasa.gov/jpeg/PIA20756.jpg[/img3][hr][/hr]Puzzles persist about possible water at seasonally dark streaks on Martian slopes, according to a new study of thousands of such features in the Red Planet's largest canyon system.
The study published today investigated thousands of these warm-season features in the Valles Marineris region near Mars' equator. Some of the sites displaying the seasonal flows are canyon ridges and isolated peaks, ground shapes that make it hard to explain the streaks as resulting from underground water directly reaching the surface. It is highly unlikely that shallow ground ice would be present as a source for seasonal melting, given the warm temperatures in the equatorial canyons.
Water pulled from the atmosphere by salts, or mechanisms with no flowing water involved, remain possible explanations for the features at these sites.
These features are called recurring slope lineae, or RSL, a mouthful chosen to describe them without implying how they form. Since their discovery in 2011, Martian RSL have become one of the hottest topics in planetary exploration, the strongest evidence for any liquid water on the surface of modern Mars, even if transient. They appear as dark lines extending downslope during a warm season, then fading away during colder parts of the year, then repeating the progression in a following year. Water, in the form of hydrated salts, was confirmed at some RSL sites last year, including in Valles Marineris. ...
Geologic Context of Recurring Slope Lineae in Melas and Coprates Chasmata, Mars - Matthew Chojnacki et al
- Journal of Geophysical Research: Planets (online 07 July 2016) DOI: 10.1002/2015JE004991
