Prof Stolper compared the signatures with a catalogue containing thousands of Earth rocks, and determined the nearest match to be an igneous type, the formation of which he likened to the production of colonial apple jack liquor.

BBC: Nasa's Curiosity rover finds 'unusual rock'

Holt, whose great-grandfather invented the first track-type tractor (which led to the formation of Caterpillar), came to the rescue in 1996.

FORBES: Magazine Article

Holt, whose great-grandfather invented the first track-type tractor (which led to the formation of Caterpillar (nyse: CAT - news - people )), came to the rescue in 1996.

FORBES: It's How You Play the Game

Another issue is that a second type of pollutant, aerosols such as the minute sulphate particles that form when sulphurous fuel is burned, promote the formation of clouds.

ECONOMIST: Changing science