Utilizing knowledge from the NASA/ESA Hubble House Telescope and NASA’s retired Spitzer house telescope, astronomers have found that two exoplanets across the pink dwarf star Kepler-138 — Kepler-138c and Kepler-138d — might be composed largely of water.
Cross-section of the exoplanet Kepler-138d; just like the Earth, this exoplanet has an inside composed of metals and rocks (brown portion), however Kepler-138d additionally has a thick layer of high-pressure water in numerous varieties: supercritical and probably liquid water deep contained in the planet and an prolonged water vapor envelope (shades of blue) above it; these water layers make up greater than 50% of its quantity, or a depth of about 2,000 km. Picture credit score: Benoit Gougeon, Université de Montréal.
Kepler-138 is an M-dwarf star roughly 218 light-years away within the constellation of Lyra.
Often known as KOI-304 or TIC 159376971, the star is about 57% the mass and 54% the radius of the Solar.
Kepler-138 is dwelling to at the very least three exoplanets: Kepler-138b, Kepler-138c and Kepler-138d.
“We beforehand thought that planets that had been a bit bigger than Earth had been large balls of metallic and rock, like scaled-up variations of Earth, and that’s why we known as them super-Earths,” stated Université de Montréal’s Professor Björn Benneke.
“Nevertheless, now we have now proven that these two planets, Kepler-138c and Kepler-138d, are fairly totally different in nature: a giant fraction of their total quantity is probably going composed of water.”
“It’s the first time we observe planets that may be confidently recognized as water worlds, a sort of planet that was theorized by astronomers to exist for a very long time.”
With volumes greater than thrice that of Earth and much twice as large, Kepler-138c and Kepler-138d have a lot decrease densities than Earth.
That is shocking as a result of a lot of the planets simply barely larger than Earth which have been studied intimately up to now all gave the impression to be rocky worlds like ours.
“Think about bigger variations of Europa or Enceladus, the water-rich moons orbiting Jupiter and Saturn, however introduced a lot nearer to their star,” stated Université de Montréal Ph.D. pupil Caroline Piaulet.
“As a substitute of an icy floor, Kepler-138c and Kepler-138d would harbor massive water-vapor envelopes.”
The inventive idea exhibits the planetary system Kepler-138. Picture credit score: SETI Institute / Danielle Futselaar.
The astronomers warning the planets might not have oceans like these on Earth straight on the planet’s floor.
“The temperature in Kepler-138c’s and Kepler-138d’s atmospheres is probably going above the boiling level of water, and we count on a thick, dense environment made from steam on these planets,” Piaulet stated.
“Solely beneath that steam environment there might probably be liquid water at excessive stress, and even water in one other section that happens at excessive pressures, known as a supercritical fluid.”
The brand new observations additionally counsel the presence of a fourth planet within the Kepler-138 system.
Named Kepler-138e, the planet is small and farther from its star than the three others, taking 38 days to finish an orbit.
The alien world is within the liveable zone of its star, a temperate area the place a planet receives simply the correct amount of warmth from its cool star to be neither too scorching nor too chilly to permit the presence of liquid water.
The character of this extra planet, nevertheless, stays an open query as a result of it doesn’t appear to transit its host star.
“As our devices and strategies grow to be delicate sufficient to seek out and examine planets which can be farther from their stars, we’d begin discovering much more water worlds like Kepler-138c and Kepler-138d,” Professor Benneke stated.
The findings seem right this moment within the journal Nature Astronomy.
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Caroline Piaulet et al. Proof for the volatile-rich composition of a 1.5-Earth-radius planet. Nat Astron, revealed on-line December 15, 2022; doi: 10.1038/s41550-022-01835-4
