GREEN bulging eyes, three heads and putrid breath? Nobody knows what life on Mars may have been like, if it existed at all, but scientists are determined to find out. Last month, the European Space Agency began work on the design of a Mars rover that will look for signs of life, and NASA has similar plans in the offing. If you believe in panspermia, however, you may already have an inkling of what to expect.
Panspermia is the idea that life on planets such as Earth and Mars was seeded from space. In the 19th century, it was championed by two of the greatest physicists of the day: William Thomson (Lord Kelvin) in England and Hermann von Helmholtz in Germany. They claimed that the “seeds” of life were spread from star to star. This theory of “cosmic panspermia” was idle speculation until the work of the Swedish Nobel prize-winning chemist Svante Arrhenius at the beginning of the 20th century.
Arrhenius tested the idea by seeing whether bacterial spores and plant seeds could survive the conditions thought to exist in interstellar space. He got botanists to expose them to a near-vacuum and temperatures as low as -196 °C, the boiling point of liquid nitrogen. On reheating, they came back to life. Nowadays, we know that bacteria can also survive the intense ultraviolet and cosmic radiation of interstellar space. As Arrhenius was the first to recognise, bacteria have quite “unearthly” properties.
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“Bacteria have some quite ‘unearthly’ properties”
According to Charles Darwin, the traits of a living organism are those that ensure its survival in the environment in which it has evolved. Two modern-day champions of panspermia, Chandra Wickramasinghe and the late Fred Hoyle, have argued that the ability to survive in space is evidence that bacteria must have originated in space.
According to Wickramasinghe and Hoyle, interstellar gas clouds are vast repositories of desiccated bacteria. When these clouds shrink under gravity to form star systems, bacteria survive inside comets. As a comet falls towards its sun and the heat boils off its surface ices, the bacteria escape into space to be swept up by planets. These bacteria, in turn, rise to the top of planetary atmospheres and get blown by sunlight into interstellar space.
Panspermia explains another puzzle: how life got started so quickly after the Earth’s birth, given that it has proved impossible to recreate in the laboratory.
Recently Max Wallis and Wickramasinghe have argued that, even if life somehow started on Earth, collisions of the planet with comets and asteroids would lead to the dispersal of terrestrial life across a large volume of the galaxy. Consequently, many millions of nascent planetary systems will be infected with Earth life and, by the same token, Earth will be infected with life from elsewhere. Perhaps our Mars rovers, instead of finding new kinds of life, will simply reacquaint us with long-lost friends.
