Science

Four of seven Earth-sized exoplanets may have large quantities of water

Hubble telescope readings indicating watery planets of Trappist-1 — including three in zone — boosts hope for life

Four of seven worlds orbiting a star might bear huge amounts of water, scientists have shown, offering a boost.

39 light-years away from Earth, seven planets orbiting the small star called Trappist-1’s solar system was discovered with the announcement.

While scientists said all the planets could harbour some water, given the perfect atmosphere, three of the four outermost planets lie inside the star’s so-called “habitable zone” — the distance where temperatures are acceptable for liquid water to exist — making them the most likely candidates.

However, it remained unclear whether some of those planets were wet. Scientists say they’re a step closer to finding out.

“What we discovered tells us that probably the [three] inner planets aren’t good planets to look for life,” said Vincent Bourrier, first author of the study from the University of Geneva.

Writing in the Astronomical Journal, an international group of researchers and Bourrier reveal how they sought to compute whether water using the Hubble space telescope to research the degree of radiation could be born by the planets.

“Knowing how much energy is emitted by a star in the ultraviolet is quite important since it can strongly impact the atmospheres of these planets,” explained Bourrier, adding that the lower energies of ultraviolet radiation can split water molecules into hydrogen and oxygen, while higher energies can be absorbed by the gases, permitting them to escape into space.

They orbit a star called an dwarf.

The group fed the planets’ distances and information on the UV radiation of the star to computer models which took into account other factors, including its zone and the star’s radiation have changed over millennia.

The results show that over years but the planet might have dropped the equivalent of 20 times the quantity of water in the oceans of the Earth. But if water loss drops after the zone is entered by a world, the four planets might have dropped less than three times the water in the oceans of Earth over years.

But the calculations assume that the planets begin with including that work on the density of these planets is required to work out how much water they formed with, an quantity of water, and the amount of water.

There’s more. “When the hydrogen flows it can form a extremely extended, comet-like tail round Earth,” stated Bourrier. “If you discover such a cloud escaping from the Trappist-1 planets, it might inform us on the existence of water which has been [lost] to the atmosphere.”

To research the possibility, the group looked in the UV radiation emitted by Trappist-1 as the next world out passed before the star — a dip in these radiation could have indicated the planet had a hydrogen “halo” absorbing energy. The observations were inconclusive.

Ignas Snellen explained the Trappist-1 system as exciting. “We’re all very eager to find out more about the probable climates on such planets, and specifically whether they could host liquid water,” he said.

However, while the study was welcomed by Snellen, he said that observations were crucial.

“Personally, I believe you could make all the calculations you would like, but ultimately we need dimensions,” he said.

Snellen added that the mystery could be solved, pointing out that the James Webb Space Telescope is set to launch and is expected to shed light on the planets’ atmospheres.

“If at least one of these planets prove to contain water it’ll be an enormous breakthrough,” said Snellen.

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