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Existential dread time: One day Earth's oceans will boil. This exoplanet might reveal when

LP 890-9c gives us a glimpse into our world's far future, astronomer tells El Reg

Astronomers are hoping to observe a super-Earth exoplanet with the James Webb Telescope to see if they can predict Earth's future as the Sun expands.

Discovered in 2022, LP 890-9c orbits a red dwarf star, located about 100 light years away, and is 37 per cent bigger than Earth. Red dwarves are cooler than our own G-class sun, so LP 890-9c orbits at just four million miles (6.4 million kilometers) from its Sun. Yet boffins think it might host liquid water.

If it does, that would place the planet in the habitable zone – a region that is sufficiently distant from a Sun to allow life to emerge, but not so hot that life can't survive or oceans boil away.

The latter fate befell Earth's hellish neighbor Venus, which lies outside the habitable zone of our solar system.

"[LP 890-9c] is fascinating because it is just at the edge of the habitable zone, at the inner edge, so closer to the Sun than the Earth, but not as close as Venus," Lisa Kaltenegger, assistant professor of astronomy at Cornell University, told The Register.

Kaltenegger is part of a team of researchers trying to figure out the limits of the habitable zone around a star. "It is exactly where a planet should still be a hot Earth but could have started on its path to water-loss and Venus-like conditions already. How hot does a planet have to get to bleed all its life-giving water to space? We don't know for sure, so this planet could help us solve that mystery," she added.

In a paper published in the Monthly Notices of the Royal Astronomical Society, the team developed different models for the planet's climate. Options include a wet and mild world like Earth, a steamy greenhouse world with a runaway greenhouse effect, or hot and barren like Venus. 

The models outline the different spectra that scopes like the Webb could observe by examining starlight filtered through the exoplanet's atmosphere. "Our research shows that the planet would look very different to a telescope if it was still a hot but habitable Earth, or if it is bleeding all its water to space, or if it is already a desolate, inhospitable Venus," Kaltenegger explained. 

The researchers plan to submit a proposal to observe LP 890-9c using the JWST. Studying the object would not only help confirm whether liquid water might exist on an exoplanet and if it might be habitable, but could also reveal what conditions might be like on Earth one day as the Sun ages and expands.

"The Sun, like every star, gets more luminous with time, so in about a half [a billion] to one billion years, it should get so hot on Earth that our oceans start to evaporate if we don't manage to reduce the sunlight hitting the Earth. But how hot is too hot? We think the energy from the star that hits LP 890-9c will make it hot, but not inhospitable yet," she hypothesized.

"If it is a habitable world, Earth might have more time than we thought before our oceans evaporate. If it is already an inhospitable world without water, then we might have less time than we thought. That is how the planet gives us a glimpse into Earth's far future." ®

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