The recurring slope lineae (RSL) are long features present in some slopes near the equator of planet Mars. Previously, it was thought that they were caused by water. However, scientists suggest that this might not be the only explanation for the presence of these formations.
Scientists discovered the RSL in 2011, while they were studying the images captured by the Mars Reconnaissance Orbiter (MRO) of NASA. Some of them suggested that the features were caused by flows of briny water. Thus, they could be the sign of an environment which could support life. They presented this idea in 2015, when they also announced that MRO found traces of salt water.
New explanation for the presence of RSL
However, this is not the only possible explanation. Some researchers suggest that RSL are the product of seasonal carbon dioxide frost. Others think that they might be traces of sand and dried dirt. A new study published on March 20th in the Nature Geoscience journal defends the latter explanation.
The study was performed by a team of scientists led by Frédéric Schmidt, from Paris-Sud University in France. They used numerical simulations to model the flow of RSL. Their models provided an interesting discovery.
Results showed that sunlight caused a “thermal creep” effect which could trigger landslides on these slopes. Thus, the heat from the sun causes the material in the RSL to move and destabilize. This is what causes the landslides. Also, the team suggested that boulders might be the main triggers of the landslides.
More evidence in favor of the dry avalanche hypothesis
Their model of the flows was accurate, as it matched with most of the RSL observed on the Garni Crater on Mars. But this modelled type of prediction is not the only evidence in favor of dry avalanches as a cause of RSL.
Scientists say that they could not identify a source of water for RSL. Condensation in the equator area of the planet was also unlikely, and the underground water-ice supplies were not stable. Also, the shape and the color of the RSL does not indicate wetness.
“We interpret the relative darker albedo appearance of the RSL as an effect of the sorting of the grains during the flow. Finer grains could also be ejected during the flow. The fading is then due to the finer aeolian [wind] grain deposition from the atmosphere.”
However, scientists need to do more research and tests until they can establish a clear explanation for the presence of recurring slope lineae on Mars.
Image Source: Wikimedia Commons