2024-01-25 22:00:17

The Hubble Space Telescope detected water vapor in the atmosphere of the smallest planet outside our Solar System, a “historic discovery” that brings astronomy one step closer to characterizing Earth-like planets.

The small exoplanet GJ 9827d, discovered in 2017 by the Kepler space telescope, is approximately twice the diameter of the Earth and orbits around a red dwarf star located 97 light years away in the constellation of Pisces, as reported this Thursday (01.25. 2024) in a statement from NASA and the European Space Agency (ESA).

Two possible classifications for the exoplanet

The team behind the discovery is examining two scenarios: either the planet is a “mini-Neptune” with a hydrogen-rich atmosphere mixed with water, or it is a hotter version of Jupiter’s moon Europa, which beneath its crust contains the twice as much water as Earth.

“The planet GJ 9827d might be half water and half rock. And there might be a lot of water vapor on top of some smaller rock body,” says Bjorn Benneke of the University of Montreal, co-leader of the research.

“Until now, we had not been able to directly detect the atmosphere of such a small planet. And now we are gradually entering this regime,” he added.

Work made possible thanks to Hubble

Over a three-year period, the Hubble telescope observed the planet for 11 transients, or events in which it crossed in front of its star.

During these motions, light from the star is filtered through the planet’s atmosphere, allowing astronomers to use Hubble’s instruments to analyze color patterns (wavelengths), which revealed the telltale signature of the molecules. of water.

An uninhabitable exoplanet

Even if GJ 9827d had a water-rich atmosphere, its Venus-like temperature of 425 degrees Celsius would make it an uninhabitable vapor world.

However, Hubble’s discovery paves the way for future studies of this and similar exoplanets, especially by the James Webb Space Telescope, which can use its high-resolution infrared images to search for more atmospheric molecules, such as carbon dioxide and methane. .

“Water on such a small planet is a historic discovery. “It brings us closer than ever to the characterization of worlds truly similar to Earth,” concludes Laura Kreidberg, from the Max Planck Institute for Astronomy (Germany).

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