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Life in a hydrogen-rich atmosphere

The exoplanet K2-18b, about 124 light-years from Earth, is a kind of mini-Neptune, as astronomers discovered this past year. It is seven to ten times heavier than Earth and its radius is 2.7 times larger. K2-18b orbits its host star, a red dwarf, once every 33 days. Thus, it is located in its star’s habitable zone.

For astronomers, however, it has one other special noteworthy feature: hydrogen, helium, and water vapor have been detected in its atmosphere. In the media, K2-18b has even been described as “Earth 2.0,” which it very definitively is not. The researchers who studied it in 2019 described it at the time as “very likely more harmful to life” than Earth.

Hydrogen in the atmosphere is not generally considered especially friendly to life: it is very reactive; any available oxygen molecules would be immediately converted to water, thus ruling out any sort of breathing as we know it. But does that mean we should write off K2-18b as a candidate for extraterrestrial life? That would be a premature conclusion according to scientists. As an experiment, they tested how life might function in a hydrogen-rich atmosphere in a laboratory.

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Blown to dust: the first exoplanet visible in a telescope is no more

In 2008, researchers looking at images from the Hubble Space Telescope found a bright spot moving around the star Fomalhaut located 25 light-years from Earth. At 400 million years old, Fomalhaut is still relatively young. The star, twice as heavy as the Sun and 17 times brighter, is also circled by a dust disk that the researchers identified as a remnant from planetary formation.

Fomalhaut b was thus the first exoplanet detected through direct, optical imaging, not just indirectly through star crossings or wobbling patterns of movements by its star. In 2015, the approximately Jupiter-sized planet was even given its own name, Dagon. However, over time, astronomers noticed a few strange things. For one, the planet appeared significantly brighter than it should have been. Its orbit also appeared to be very eccentric, with an orbital period of 2000 years and its distance to its star varying between 49 and 290 astronomical units.

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