The Closest Earth-Like Exoplanet May Not Be Habitable After All

Wednesday, 13 December 2017 - 11:16AM
Space
Astronomy
Alien Life
Wednesday, 13 December 2017 - 11:16AM
The Closest Earth-Like Exoplanet May Not Be Habitable After All
In 1961, the famous Drake Equation strung together seven variables to give an estimate of how many detectable alien civilizations are out there, but one variable in particular has been causing scientists some major trouble: the average number of planets that can potentially support life.

To figure that out, we have to take a step back and figure out what separates habitable planets from blasted, irradiated hellscapes.

Previously, being a small, rocky planet with the potential for water orbiting in a star's "habitable zone" was considered enough, but recent papers authored by scientists at Princeton examining Proxima Centauri b, the closest "habitable" exoplanet, have a much gloomier outlook: it turns out that solar (or stellar) wind may be a much bigger threat to life-supporting planets than we ever imagined.

Solar wind consists of streams of charged particles radiating from a star. Here's a short video explaining how they work:



The Earth is relatively well-protected from solar wind by its magnetic field, which keeps our atmosphere intact, but other planets can have their entire atmospheres ripped apart by solar winds, especially if their star is younger and more volatile:

Opening quote
"Traditional definition and climate models of the habitable zone consider only the surface temperature," lead author Chuanfei Dong of Princeton University said in a statement. "But the stellar wind can significantly contribute to the long-term erosion and atmospheric loss of many exoplanets, so the climate models tell only part of the story."
Closing quote


This may be the case for Proxima Centauri b, which is about four light-years away from Earth—relatively close for an exoplanet. Proxima b is rocky and the right distance from its star, but Dong's team's research into solar wind made it clear that any chance to support life on the planet (and others like it) could have evaporated with its atmosphere long ago. This means that not only does a planet need water, a friendly atmosphere, and a good temperature, but it also needs to hold onto those traits for billions of years:

Opening quote
"Our results indicate that [Proxima Centauri b] and similar exoplanets are generally not capable of supporting an atmosphere over sufficiently long timescales when the stellar wind pressure is high," Dong said.
Closing quote


It's not time to give up hope, however—at least we know that bacterial life could potentially survive for millions of years even in the face of hardcore radiation, extreme temperatures, and a thin atmosphere.

When it comes to back-up Earths, however, finding a good fallback planet might take longer than we thought.
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