CUTTING EDGE

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Hunting for life, but not as we know it

Ammonia could be as important on other worlds as oxygen is on ours

Prof Lewis Dartnell is an astrobiologist at the University of Westminster

Over the coming years, as astronomers use spectroscopy to read the atmospheres of Earthsized, habitable planets, detecting the presence of one gas will be an important discovery: oxygen. On Earth, oxygen is released by life – specifically, by organisms using sunlight for energy.

Oxygen is a very reactive gas. Early in Earth's α history any oxygen released into the atmosphere was rapidly removed. It reacted with rocks, or was destroyed by photochemical reactions driven by ultraviolet rays in sunlight. Such processes are known as 'sinks', and oxygen only started to accumulate in Earth's atmosphere once its production had overwhelmed these sinks. An oxygen-rich atmosphere is thought to be a sign of flourishing life on a world, which is why astronomers would be so excited about discovering one on an exoplanet.