Twin planets orbiting a distant star may be half water

A brace of duplicate planets called Kepler-138 c and d look to beryllium h2o worlds, with steamy atmospheres and oceans that instrumentality up fractional their full volume

Space 15 December 2022

By Leah Crane

Kepler-138 d (front), Kepler-138 c (left) and Kepler 138 b passing successful beforehand of its genitor star

NASA, ESA, Leah Hustak (STScI)

Two unusual planets 218 airy years distant whitethorn beryllium wholly covered successful oceans 500 times deeper than Earth’s. While determination astir apt isn’t beingness connected these duplicate water worlds, called Kepler-138 c and d, determination whitethorn beryllium a batch much of them scattered passim the universe.

Both exoplanets orbit a prima called Kepler-138 and were recovered successful 2014. The observations astatine the clip hinted that they were reasonably antithetic worlds from 1 different but that they were made mostly of rock. Now, Caroline Piaulet astatine the University of Montreal and her colleagues person taken a caller acceptable of observations utilizing the Hubble and Spitzer abstraction telescopes, arsenic good arsenic the W. M. Keck Observatory successful Hawaii, that bespeak otherwise.

While the prima was antecedently thought to person lone 3 planets, these observations showed grounds of a 4th world. Including that other satellite successful simulations of the strategy revealed that Kepler-138 c and d are acold much akin than researchers initially thought. Each is simply a small much than doubly arsenic monolithic arsenic Earth with astir 1.5 times Earth’s radius.

By plugging those caller numbers into their models, the researchers recovered that up to fractional of the measurement of each satellite indispensable beryllium made of thing lighter than stone but heavier than the hydrogen and helium ubiquitous successful gaseous worlds – the astir apt mentation is water. “It tin beryllium different molecules that would person a akin density to h2o – methane oregon ammonia would beryllium bully alternatives – but the crushed wherefore we deliberation it’s astir apt h2o is that h2o is the astir abundant of these alternatives successful the universe,” says Piaulet.

However, contempt its value for life, h2o does not needfully marque a satellite habitable. Kepler-138 c and d are some comparatively adjacent to their star, truthful alternatively of the icy shells that people astir of the water-laden worlds successful our ain star system, they astir apt person dense atmospheres of steam. Beneath the atmosphere, temperatures are expected to scope beyond 200°C and pressures would beryllium astatine slightest 100 times the aboveground unit connected Earth – possibly arsenic overmuch arsenic thousands of times higher.

“These astir apt aren’t the champion planets for life,” says Piaulet. “But the information that these beryllium means that determination could beryllium planets with compositions similar this, but conscionable a tiny spot further from their big stars, and that opens the doorway to a wholly caller benignant of habitable world.”

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

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