June 12, 2019
Astronomers Reveal Why Planets That Support Alien Life Could Be Rarer Than We Once Thought

Scientists have long been pondering the question of whether there are other planets in the universe that have the ingredients necessary to support alien life. While there have been multiple studies over the years hinting at this possibility, new research suggests that previous estimates of the number of planets capable of sustaining extraterrestrial life may have been way too optimistic.

In a study published this week in The Astrophysical Journal and cited by USA Today, a team of astronomers revealed that it is impossible for "complex" ecosystems like the ones found on Earth to exist in majority of the "traditionally defined" habitable zone, or parts of the universe with planets that could allow liquid water to form. While it was explained that such a zone could plausibly allow advanced forms of life to thrive, the researchers noted that most planets within it have rich concentrations of toxic gases in their atmospheres, thus preventing them from supporting complex life.

Regarding planets in the habitable zone, the researchers pointed out that these worlds could — in theory — support some forms of alien life. However, these forms of life only include "basic" creatures like single-celled microbes, as opposed to different species of animals that may range from "simple" sponges to humans.

The methodologies used to come up with the findings were detailed in a separate Newsweek report, which explained that the researchers made use of computer modeling to simulate a range of conditions on multiple planets within the habitable zone. The results of these simulations revealed that most of the planets analyzed would require "substantially more" carbon dioxide than the already high levels found in Earth's atmosphere in order to keep temperatures warm enough for complex life to survive.

All in all, there are about 4,000 planets that have been considered by scientists to be potentially habitable. However, the study suggests that only a third of these planets might be capable of supporting humans and other complex life forms.

"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," read a statement from NASA's Edward Schwieterman, lead author on the new study.
"That's far beyond the levels known to be toxic to human and animal life on Earth."
As further noted by Schwieterman, his team's study proves that Earth is a "rare and special" planet, given that it's the only known planet in the universe that is capable of supporting human life. He added that the research "only enhances the case" for protecting our planet from a variety of threats.

According to the New York Post, the new research "puts a further damper" on the potential of finding advanced alien life in nearby worlds, as it also explained how TRAPPIST-1, Proxima Centauri, and other stars are among those that have enough ultraviolet radiation to result in high atmospheric concentrations of carbon monoxide -- another gas widely considered to be dangerous to complex life.