Eaten away by ‘vog’: Acid fog eroding rocks on Mars

The planet Mars showing showing Terra Meridiani is seen in an undated NASA image. © Greg Shirah
Scientists believe they have figured out why rocks on Mars are eroding. They say an acidic fog created by volcanic eruptions on the red planet is the probable culprit.

Planetary scientist Shoshanna Cole came up with the theory after studying a 100-acre area on Husband Hill in the Columbia Hills of the Gusev Crater on Mars using data gathered by a number of instruments on the 2003 Mars Exploration Rover Spirit.

She found that acidic vapors released by eruptions may have been responsible for eating away rocks on the Watchtower Class outcrops on the Cumberland Ridge and Husband Hill summit.

“The special thing about Watchtower Class is that it’s very widespread and we see it in different locations. As far as we can tell, it is part of the ground there,” which means that these rocks record environments that existed on Mars billions of years ago, Cole said in a press release submitted by the Geological Society of America.

She combined data from previous studies of the red planet and found some interesting patterns emerging. The Mars Exploration Rover Sprit had closely examined the Watchtower Class rocks at a dozen locations spanning 200 meters across the Cumberland Ridge and the Husband Hill summit.

Cole found that the chemical composition of the rocks was the same, but they looked different. Some had lost their structure and become less crystalline and more amorphous.

“So we can see the agglomerations progress in size from west to east and the iron changes in the same way,” Cole said. “It was super cool.”

The fact that the rocks had the same composition indicated to Cole that they had once been identical. “That makes us think that they were made of the same stuff when they started out. Then something happened to make them different from each other,” the scientist added.

She believes that the rocks were exposed to acidic water vapor from volcanic eruptions, which is similar to the corrosive volcanic smog or “vog” that poses dangers in Hawaii.

“When the Martian ‘vog’ landed on the surface of the rocks it dissolved some minerals, forming a gel. Then the water evaporated, leaving behind a cementing agent that resulted in the agglomerations,” Cole mentioned.

“So nothing is being added or taken away, but it was changed,” Cole said. “This would have happened in tiny amounts over a very long time. There’s even one place where you see the cementing agent healing a fracture. It’s pretty awesome. I was pretty happy when I found that one.”

The findings were presented at the Geological Society of America’s annual meeting, which took place in Baltimore.