Today we were greeted with an announcement, which, if validated, will have profound implications for the search for extraterrestrial life on other planets and moons in the Universe.

Researchers in the US have discovered a bacterium that uses arsenic instead of phosphorous in its basic biochemistry. To date, all living organisms – from whales to fungi to the simplest micro-organisms – use just six elements in their fundamental chemical make-up: hydrogen, oxygen, carbon, nitrogen, sulphur and phosphorous. Arsenic is chemically similar to phosphorous, but usually when used instead of phosphorous, it can disrupt metabolic pathways causing cell damage and death. This new bacterium, GFAJ-1, has found a way to use the element successfully in arsenic rich environments, proving that life is even more tenacious and adaptive than we could have imagined.

GFAJ-1 is not a totally different life-form. It’s DNA is based on conventional DNA and so it is tied in some way to all other known organisms on this planet. However the door is now opened, just slightly, to the possibility of a “shadow biosphere” – living organisms that are completely different to any known lifeform in this world. Such a discovery would be monumental. It is almost certain to be an area of feverish research in the coming years.

While we are some way off finding life on other planets, the discovery provides us with more evidence that living organisms may exist in worlds very different to our own. Saturn’s moon Titan, for instance, has a carbon rich environment; but its temperature is far lower than any place on Earth. Earth-bound organisms, because of their basic chemistry, would perish in such a world. Creatures with a different biochemistry, however, might find a way to survive on Titan, hence the importance of the announcement today.

The research is likely to be challenged robustly in the coming months and years, but if validated, it will provide new lines of investigation for scientists interested in making the discovery of the century – the finding of truly alien lifeforms.

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