There is, however, another way to answer this giant question. In 1989, Prof Pillingers team found organic material, typical of that left by the remains of living things on Earth, in a meteorite called EETA79001. This is one of a relatively small number of rocks fewer than 100 that chemical analysis reveals must have been blasted off the surface of the Red Planet by an asteroid impact and then subsequently fallen to Earth.
The Open University team stopped short of saying they had discovered life on Mars but, in 1996, Everett Gibson and his colleagues at Nasa announced that they believed that they had discovered a fossil no bigger than a nanometre in another meteorite, known as ALH84001, which had fallen to Earth roughly 13,000 years ago. Other researchers, studying the data collected by Americas Viking landers, which touched down in 1976, concluded that life signs had been detected then, too.
Sceptics and there are many remain convinced that inorganic processes could have produced the same data and features that have been interpreted by some as signs of microbial life. But how can we even tell these rocks came from Mars?
Well, a few days ago, I found myself back at the Open University, to test another Martian meteorite, which we will offer as a prize to readers of New Scientist in the next issue. I bought it from Luc Labenne, a well-known collector based in France. It was a piece of a rock that crashed into the desert in Algeria, hence the designation NWA2975 .
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