Alien worlds are less hospitable to complex life than scientists thought

New research suggests the conditions necessary for complex life forms may be even rarer than planetary scientists previously thought. Researchers determined the buildup of toxic gases in the atmosphere makes most exoplanets uninhabitable.

Planetary scientists classify alien planets as being "habitable" or in the "habitable zone" if they're close enough to their host star to keep some of their water liquid, or unfrozen, but not so close it all evaporates away.

According to a new study published Monday in the Astrophysical Journal, the simple habitability definition is perfectly fine for basic life forms, like microbes, but not for more complex organisms.

When scientists accounted for the likely levels of toxic gases in the atmospheres of so-called habitable planets, they found only a small percentage could host complex life forms.

"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," Timothy Lyons, a professor of biogeochemistry at the University of California, Riverside, said in a news release.

Scientists used simulations to study climate and chemistry dynamics in the atmospheres of several different planets. First, scientists focused on CO2. For planets on the outer edge of the habitable zone, carbon dioxide is necessary to keep the planet warm enough to host liquid water. But models showed the amount of CO2 necessary to do so would be well above the threshold considered safe for plants and animals.

When accounting for CO2 alone, scientists determined only half of the universe's known habitable zones could actually host complex life. Researchers were able to eliminate entire star systems by considering the presence of carbon monoxide. Cooler, dimmer stars like Proxima Centauri and TRAPPIST-1 produce a lot of ultraviolet radiation, which triggers the production of carbon monoxide in the atmosphere. Small amounts of carbon monoxide can prevent the movement of oxygen throughout an animal's circulatory system -- proving deadly. On Earth, the sun's powerful rays drive chemical reactions that destroy carbon monoxide.

With the database of so-called habitable planets getting bigger and bigger, scientists need to begin narrowing their focus.

"Our discoveries provide one way to decide which of these myriad planets we should observe in more detail," said Christopher Reinhard, a former UCR graduate student now an assistant professor at the Georgia Institute of Technology. "We could identify otherwise habitable planets with carbon dioxide or carbon monoxide levels that are likely too high to support complex life."

Related Links
Lands Beyond Beyond - extra solar planets - news and science
Life Beyond Earth

Tweet

Thanks for being there;
We need your help. The SpaceDaily news network continues to grow but revenues have never been harder to maintain.

With the rise of Ad Blockers, and Facebook - our traditional revenue sources via quality network advertising continues to decline. And unlike so many other news sites, we don't have a paywall - with those annoying usernames and passwords.

Our news coverage takes time and effort to publish 365 days a year.

If you find our news sites informative and useful then please consider becoming a regular supporter or for now make a one off contribution.

SpaceDaily Monthly Supporter
$5+ Billed Monthly

paypal only

SpaceDaily Contributor
$5 Billed Once

credit card or paypal

Exomoons may be home to extra-terrestrial life
Lincoln UK (SPX) Jun 06, 2019
Moons orbiting planets outside our solar system could offer another clue about the pool of worlds that may be home to extra-terrestrial life, according to an astrophysicist at the University of Lincoln. Exoplanets are planets outside our solar system and up to this point nearly 4,000 have been discovered. Only a small proportion of these are likely to be able to sustain life, existing in what is known as the habitable zone. But some planets, especially large gas giants, may harbour moons which con ... read more