The Curiosity rover has found more evidence that Mars was once a wet planet in the form of a kind of rock that usually forms out of drying mud. After spotting a pattern of cracks that usually forms when mud dries, the Curiosity team had the rover backtrack to a location called Squid Cove. The mud in this cove is believed to have dried approximately three billion years ago, forming Squid Cove’s current mudstone formations. Mudstone is a type of sedimentary rock that forms from drying mud with sediment mixed in.
Curiosity’s Mastcam spotted a pattern of polygons measuring about ½ to 1 inch across and outlined by ridges. The cracks may have filled with sediment and mud that were delivered by wind activity and dried. Layers of rock, sediment and mud formed over these sediment-filled cracks and provided enough pressure to turn the material in the cracks into rock. Then the overlaying material eroded away, revealing the sediment-filled cracks as a series of ridges. The results are evidence of a dry period in between wetter periods that may have included lakes.
Like We Really Need More Evidence of Water, Right?
LOL, right. This isn’t even the first time that Curiosity has discovered evidence of past water activity on Mars. It has found mudstone above its current location at Squid Cove and additional evidence of ancient lakes in the area while exploring older rock layers. This is simply proof that the lake may have partially or completely dried out and then refilled at some point in the distant past.
Could There Still Be Water?
The short answer is, “Yes.” The long answer is that Curiosity recently discovered evidence of an underground reservoir of liquid water under Gale Crater. Previous evidence had pointed to the idea that any water remaining on Mars would be in the form of permafrost mixed into the Martian regolith.
The liquid water under the surface is probably mixed with a type of salt called calcium perchlorate, which lowers the freezing temperature of water. The resulting brine is probably too salty to safely drink without distilling out the salt first. If Mars had conditions friendlier toward life, such as less radiation, a thicker atmosphere and warmer temperatures, some halophiles may be able to survive in the brine. However, any life on Mars is believed to have died out one billion years ago.
Much of Mars’ ancient water is believed to have evaporated when it began losing its atmosphere. Signs of ancient water activity remain in geological structures like the mudstones in Squid Cove.