Microorganisms can thrive in a 100% hydrogen atmosphere

Simulated Image of an Earth-like Exoplanet

Simulated Image of an Earth-like Exoplanet

"We're trying to expand people's view of what should be considered a habitable planet", says exoplanet astronomer Sara Seager of MIT (SN: 10/4/19). A final set of bottles was left with Earth air.

Global researchers have found microorganisms can survive and grow in an atmosphere of 100 per cent hydrogen - suggesting life could potentially thrive in more environments than previously thought. The molecular hydrogen persisted in the atmosphere for hundreds of millions of years up to the Great Oxidation Event.

Seager and her team studied two microbes' tolerance to 100 percent hydrogen environments: the first was the bacteria Escherichia coli, and the second, yeast.

During the study, the researchers observed that microbes could withstand and flourish in an atmosphere that is rich in hydrogen. In order to maintain a hydrogen-only atmosphere, these exoplanets would either have to be colder than Earth, have stronger gravity at their surface, or have a way to replenish the hydrogen in their atmosphere-and it's hard to say what effects any of these changes would have on life. They incubated the microorganisms in four bottles with different gas concentrations: one with regular air, one with 100 per cent hydrogen, one with 100 per cent helium, and one with 20 per cent carbon dioxide and 80 per cent nitrogen.

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Hydrogen is much lighter than oxygen or nitrogen, so a hydrogen world's atmosphere would extend much further out from the planet's rocky surface, making them easier to spot and easier to study than smaller, Earth-like exoplanets, especially when next generation telescopes like NASA's upcoming James Webb Space Telescope come online. These important findings suggest that life might appear in a variety of extraplanetary environments that scientists previously discounted.

Billions of years ago, Earth had very small amounts of hydrogen in its primordial atmosphere, up to about 0.1%. Hikers attempting to hike to the summit run out of air, due to the fact that the density of all atmospheres drop off exponentially with height, and based on the dropping off distance for our nitrogen- and oxygen-dominated atmosphere.

Scientists would love to know whether there's life elsewhere in the universe, and part of answering that question is determining what an inhabited exoplanet would look like to our telescopes here on Earth. The astrophysicist visualizes hydrogen-dense minerals and oceans, as all life needs liquid to survive. "But it doesn't necessarily have to be a different world".

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