Slope Streaks Or RSL?

Image Credit: NASA/JPL-Caltech/Univ. of Arizona

December 20, 2016 – This image shows a region where there are many slope streaks, typically dark features on slopes in the equatorial regions on Mars. The streaks may extend for tens of meters in length and gradually fade away with time as new ones form. The most common hypothesis is that they are generated by dust avalanches that regularly occur on steep slopes exposing fresh dark materials from underneath the brighter dust.

There are many types of slope streaks but one of the most recent and significant findings using HiRISE was the discovery of a new type of streak called “recurring slope lineae,” or RSL for short. Recent studies suggest that RSL may form through the flow of briny (extremely salty) liquid water that can be stable on the surface of Mars even under current climatic conditions for a limited time in summer when it is relatively warm.

How can scientists distinguish between conventional slope streaks like the ones seen here and RSL? There are many criteria. For instance, RSL are usually smaller in size than regular slope streaks. However, one of the most important conditions is seasonal behavior, since RSL appear to be active only in summer while regular slope streaks can be active anytime of the year.

This site is monitored regularly by HiRISE scientists because of the high density of slope streaks and their different sizes and orientations. A time-lapse sequence (below) shows that a new slope streak has formed in the period since April 2016 (and it is darker in comparison to the others indicating its freshness). However, this period corresponds mainly to the autumn season in this part of Mars — and there were not any major changes in the summer season. This suggests that the feature that developed is a regular slope streak like others in the area.

A time-lapse sequence shows that a new slope streak has formed on Mars. Image Credit: NASA/JPL-Caltech/Univ. of Arizona

The University of Arizona, Tucson, operates HiRISE, which was built by Ball Aerospace & Technologies Corp., Boulder, Colorado. NASA’s Jet Propulsion Laboratory, a division of Caltech in Pasadena, California, manages the Mars Reconnaissance Orbiter Project for NASA’s Science Mission Directorate, Washington. The Mars Reconnaissance Orbiter, built by Lockheed Martin Space Systems in Littleton, Colorado, has been orbiting Mars since 2006.