The London fog might be bad — but at least the country isn’t being eaten away by an acidic vapour that is spewing out of its volcanoes.
That is what is happening on Mars, where a fog is gradually eating away the rocks that cover its surface.
Nasa’s Spirit Rover has spotted strange rock formations on Mars’s Gusev Crater that seem to indicate that an acidic vapour is gradually wearing them down.
On the planet’s Cumberland Ridge, rocky outcrops have been seen with small bumps or agglomerations, which are thought to be a consequence of minerals inside of them losing their structure.
Instruments on the rover also revealed that something had reacted with iron in the rocks to varying degrees.
In other respects, the composition of the rocks was identical.
Planetary scientist Dr Shoshanna Cole, from Ithaca College, New York, said: "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."
Dr Cole believes the rocks were exposed to acidic water vapour from volcanic eruptions similar to the corrosive "vog" in Hawaii.
When the Martian vog touched the surface of the rocks, it dissolved away some of the minerals, forming a gel, according to the theory. Then the water evaporated leaving the agglomerations behind.
"Nothing is being added or taken away, but it was changed," Dr Cole added. "This would have happened in tiny amounts over a very long time."
The more altered rocks, with larger agglomerations, were found in shadier spots on steep slopes facing away from the sun.
Previous laboratory experiments had shown that when Martian basalt rocks are exposed to sulphuric and hydrochloric acids, they lose their crystalline structure in just the same way.
The findings were presented at the Geological Society of America's annual meeting in Baltimore.
Additional reporting by Press Association
