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Could life thrive on hydrogen-rich alien worlds?

Life can thrive in a 100% hydrogen atmosphere, according to a new study. The finding could completely change our understanding of how (and where) life might exist in the universe. 

For the study, a team of researchers led by Sara Seager, an astrophysicist and planetary scientist at the Massachusetts Institute of Technology (MIT), conducted experiments with the bacteria Escherichia coli, or E. Coli, and yeast. They put these species in a 100% hydrogen atmosphere. And, incredibly, the microbes survived, showing how life can live in such an extreme atmosphere. (For contrast, hydrogen makes up less than one part per million of Earth's atmosphere, which consists of mostly nitrogen.)

"I want to push astronomers to think more broadly about what kind of planets might be habitable," Seager told Space.com in an email. "Biologists, if they ever thought of hydrogen-rich atmospheres, would think it's fine for life to survive, because hydrogen is not known to be toxic to life" she said. However, she noted, astronomers "are not aware that life can survive in hydrogen-dominated atmospheres, so our work was to give a clear and concise experimental evidence that it is so."

So, Seager explained, researchers might consider studying exoplanets— or planets outside the solar system — that they otherwise wouldn't target in the search for alien worlds that could potentially support life. Additionally, because hydrogen-heavy atmospheres are usually larger and more extended from their planet's surface, they could be easier to spot with some observing techniques, she added. 

Studying microbes

The microbes that Seager and her team studied in the lab grew more slowly in the 100% hydrogen atmosphere than they would in a "normal" Earth environment, Seager said. "A few times more slowly for E. Coli and a few hundred times more slowly for yeast," she said. However, she added that "this isn't too surprising, because without oxygen the microbes have to get all their food from fermentation, and that just doesn't yield as much energy."

While this experiment showed how life can survive in a pure hydrogen atmosphere, scientists don't expect to find exoplanets with atmospheres made up of 100% hydrogen. Still, they do expect to find some exoplanets with hydrogen-dominated atmospheres, Seager said. 

Looking to the stars

These findings are especially important to the search for life because, although they haven't found them yet, astronomers think that there are likely large, rocky exoplanets with thin, hydrogen-rich atmospheres, Seager said. 

"We don't know any planets like that — yet," Seager said. "Theory says they should exist … However, Jupiter, Saturn, Uranus, Neptune, giant exoplanets [and] mini Neptunes all have H2 [Hydrogen] and He [Helium] dominated atmospheres — though no one thinks life is there."

Going forward, knowing that life can survive in hydrogen, researchers could expand their observations of far-off exoplanets and their atmospheres. They could expand their gaze to look for such planets they might have otherwise overlooked while making observations with existing technology. Additionally, when tools like NASA's James Webb Space Telescope launch to space (the space telescope is currently set to launch in March 2021), they will be able to get even better observations. 

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