In an announcement made this morning, NASA stated that the Mars Reconnaissance Orbiter (MRO) has detected "the strongest evidence yet" of liquid water on the fourth planet from the Sun. 

The new evidence emerged from data collected by an imaging spectrometer mounted on the spacecraft, which was launched in 2005 and has been orbiting Mars since 2006. According to the announcement, "researchers detected signatures of hydrated minerals on slopes where mysterious streaks are seen on the Red Planet." The signatures appear to corroborate existing hypotheses.

Known as recurring slop lineae (RSL), the streaks seem to ebb and flow, apparently in accord with seasonal fluctuations. Previously suggested as an indicator of the presence of water, the discovery of hydrated salts further validates this idea.

The salts – likely a mixture of magnesium perchlorate, magnesium chlorate, and sodium perchlorate – would help lower the freezing point of what is likely a subsurface flow that occasionally breaches the surface.

Lujendra Ojha, the lead author of the report, first identified the RSL streaks when he was an undergraduate student analyzing images from the MRO's High Resolution Imaging Science Experiment. The findings emerged after pairing those images with "mineral mapping by MRO’s Compact Reconnaissance Imaging Spectrometer for Mars."

"When most people talk about water on Mars, they're usually talking about ancient water or frozen water," Ojha states in the announcement. "Now we know there’s more to the story. This is the first spectral detection that unambiguously supports our liquid water-formation hypotheses for RSL."