NASA's Mars Reconnaissance Orbiter has transmitted further measurements of curious seasonal marks on the surface of Mars. They could be the most compelling evidence yet of flowing water existing on the Red Planet in the present day.
The features themselves are called recurring slope lineae (RSL) and take the form of dark finger-like lines progressing down the Martian slopes. The flows are not found all around the planet, and only seem to occur during the hotter seasons. It has also been observed that the features are more prevalent some years than they are in others, and this in turn makes them more difficult to predict and sample.
The observations sent back by the orbiter show seasonal variations in iron minerals on slopes where RSL appear. Researchers such as Lujendra Ojha, a graduate student at the Georgia Institute of Technology, Atlanta, are currently searching for minerals left in the wake of these RSLs via spectral analysis, in an attempt to further understand the features.
Unfortunately there were no elements of the spectral analysis which pointed to the presence of water or salts in RSL, but revealed instead a higher than normal concentration of ferric and ferrous minerals.
However, these results may not necessarily preclude the presence of water in an RSL. The area of ground covered by the spectral analysis is much greater than the relatively thin strips of land that comprise the dark flows. It has therefore been postulated that the method of analyzing the features is not entirely adequate. Another factor compromising the effectiveness of the results is that the observations are only made in afternoons, and therefore could fail to detect any morning moisture traces.
Regarding the composition of the RSLs, Ojha stated that "We still don't have a smoking gun for existence of water in RSL, although we're not sure how this process would take place without water." Despite the lack of evidence in the spectral analysis, the current leading theory on the RSLs is a flow of water beneath the surface bleeding up to cause the patterns.
"The flow of water, even briny water, anywhere on Mars today would be a major discovery, impacting our understanding of present climate change on Mars and possibly indicating potential habitats for life near the surface on modern Mars," said Richard Zurek, a project scientist for the Reconnaissance Orbiter Project.