Extraterrestrial life ‘could be much, much rarer than we thought’, new study suggests

Rob Waugh
The 'habitable zone' might not be as habitable as we all thought (Photo digital Illustration by NASA/NASA via Getty Images)

The reason that radio telescopes on Earth have never tuned in to a message from E.T. could be a rather depressing one - there might be far fewer aliens out there than we thought.

Researchers at UC Riverside have discovered that many supposedly ‘habitable’ planets might be toxic gas-shrouded hell worlds unable to support life.

It’s all to do with the ‘habitable zone’ used to locate ‘livable’ planets, - which might be far less livable than we thought.

The researchers write, in research published in the Astrophysical Journal, that the ‘safe zone’ is often half the size researchers previously imagined (and in some cases, doesn’t exist at all).

The find could have important implications for the search for life off Earth (including in nearby Proxima Centauri, the researchers write).

Professor Timothy Lyons of UC Riverside says, ‘This is the first time the physiological limits of life on Earth have been considered to predict the distribution of complex life elsewhere in the universe.’

‘Imagine a ‘habitable zone for complex life’ defined as a safe zone where it would be plausible to support rich ecosystems like we find on Earth today.

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‘Our results indicate that complex ecosystems like ours cannot exist in most regions of the habitable zone as traditionally defined.

The researchers found that some planets would have to have toxic levels of carbon dioxide.

Lead author Edward Schwieterman said, ‘To sustain liquid water at the outer edge of the conventional habitable zone, a planet would need tens of thousands of times more carbon dioxide than Earth has today.

‘That’s far beyond the levels known to be toxic to human and animal life on Earth.’

No safe zone at all exists for certain stars, including two of the sun’s nearest neighbors, Proxima Centauri and TRAPPIST-1.

The type and intensity of ultraviolet radiation that these cooler, dimmer stars emit can lead to high concentrations of carbon monoxide, another deadly gas.

The new study concludes that carbon dioxide toxicity alone restricts simple animal life to no more than half of the traditional habitable zone.

For humans and other higher order animals, which are more sensitive, the safe zone shrinks to less than one third of that area.