HUMANITY’S search for aliens has hit a hurdle after scientists admitted to a major mistake in how they look for habitable planets.
It turns out half the planets that we thought could harbour life are in fact dead worlds enveloped by suffocating toxic gases.
We pick out potential alien worlds based on whether or not they’re in a star’s “habitable zone”.
This is a safe zone where a planet is just the right temperature to hold liquid water – too close to the star and it’ll evaporate, too far and it’ll freeze.
But researchers at the University of California, Riverside, say our estimates of stars’ habitable zones have been far too generous.
Taking into account levels of toxic gases like carbon monoxide and dioxide, more than half the planets in a star’s habitable zone wouldn’t be able to host complex life, experts found.
“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,” said lead scientist Professor Timothy Lyons.
“Our results indicate that complex ecosystems like ours cannot exist in most regions of the habitable zone as traditionally defined.”
Experts used computer models to look at the climate on a variety of planets.
Worlds too far from their star need carbon dioxide – a potent greenhouse gas – to trap in heat and maintain temperatures above freezing.
But according to the calculations, planets on the edge of habitable zones would need toxic levels of carbon dioxide to hit the right temperature to grow life.
“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,” said team member and Nasa scientist Dr Edward Schwieterman.
“That’s far beyond the levels known to be toxic to human and animal life on Earth.”
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 intelligent animals, which are more sensitive, the safe zone shrinks to less than one third of that area.
What is a habitable zone?
Here’s everything you need to know…
- The habitable zone is the area around a star where it is not too hot and not too cold for liquid water to exist on the surface of surrounding planets.
- Imagine if Earth was where Pluto is. The Sun would be barely visible (about the size of a pea) and Earth’s ocean and much of its atmosphere would freeze.
- On the other hand, if Earth took Mercury’s place, it would be too close to the Sun and its water would form a steam atmosphere, quickly boiling off.
- The distance Earth orbits the Sun is just right for water to remain a liquid. This distance from a star is called the habitable zone, or the Goldilocks zone.
- Rocky exoplanets found in the habitable zones of their stars, are more likely targets for detecting liquid water on their surfaces.
- Why is liquid water so important? Life on Earth started in water, and water is a necessary ingredient for life (as we know it).
But all hope isn’t lost just yet – the team reckon their results will actually help in our hunt for ET, as it narrows down our options when it comes to pick which planets to explore.
“Our discoveries provide one way to decide which of these myriad planets we should observe in more detail,” said team member Christopher Reinhard.
The research was published in The Astrophysical Journal.
In other ET news, Nasa reckons we’re on course to find alien life “within the next few decades”.
Aliens may be hiding on a ‘freezing, shadowy world’ just six light years from Earth, scientists claim.
And experts think aliens will ‘probably fire space LASERS’ at us – rather than visiting from Super Earth planets.
Do you think Nasa will discover alien life within your lifetime? Let us know in the comments!
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