Twin planets orbiting a distant star may be half water

A pair of dual planets known as Kepler-138 c and d seem like water worlds, with steamy atmospheres and oceans that take up half their whole quantity

By Leah Crane

Two unusual planets 218 mild years away could also be fully lined in oceans 500 instances deeper than Earth’s. While there most likely isn’t life on these twin water worlds, known as Kepler-138 c and d, there could also be much more of them scattered all through the universe.

Both exoplanets orbit a star known as Kepler-138 and had been present in 2014. The observations on the time hinted that they had been pretty totally different worlds from each other however that they had been made largely of rock. Now, Caroline Piaulet on the University of Montreal and her colleagues have taken a brand new set of observations utilizing the Hubble and Spitzer area telescopes, in addition to the W. M. Keck Observatory in Hawaii, that point out in any other case.

While the star was beforehand thought to have solely three planets, these observations confirmed proof of a fourth world. Including that additional planet in simulations of the system revealed that Kepler-138 c and d are much more comparable than researchers initially thought. Each is a bit more than twice as large as Earth with about 1.5 instances Earth’s radius.

By plugging these new numbers into their fashions, the researchers discovered that as much as half of the quantity of every planet should be manufactured from one thing lighter than rock however heavier than the hydrogen and helium ubiquitous in gaseous worlds – the most certainly rationalization is water. “It can be other molecules that would have a similar density to water – methane or ammonia would be good alternatives – but the reason why we think it’s most likely water is that water is the most abundant of these alternatives in the universe,” says Piaulet.

However, regardless of its significance for all times, water doesn’t essentially make a planet liveable. Kepler-138 c and d are each comparatively near their star, so as an alternative of the icy shells that mark many of the water-laden worlds in our personal photo voltaic system, they most likely have dense atmospheres of steam. Beneath the environment, temperatures are anticipated to succeed in past 200°C and pressures could be at the very least 100 instances the floor strain on Earth – maybe as a lot as 1000’s of instances greater.

“These probably aren’t the best planets for life,” says Piaulet. “But the fact that these exist means that there could be planets with compositions like this, but just a tiny bit further from their host stars, and that opens the door to a completely new type of habitable world.”

Journal reference: Nature Astronomy, DOI: 10.1038/s41550-022-01835-4

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