The Hubble Space Telescope has observed that the smallest known planet outside the solar system contains water in its atmosphere, the American (NASA) and European (ESA) space agencies announced Thursday.
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“Water on such a small planet is a remarkable discovery,” said Laura Kreidberg of the Max Planck Institute for Astronomy in Germany, co-director of the research. “This brings us closer than ever before to describing truly Earth-like worlds.”
The planet in question, GJ 9827d, which has a diameter about twice that of Earth, is located in the constellation Pisces, 97 light-years or more than 900,000 billion kilometers away, according to a press release from NASA and ESA.
These officials believe the planet is either a “mini-Neptune” – with a hydrogen-rich, water-rich atmosphere – or a hotter version of Jupiter's moon Europa, which contains twice as much water as Earth beneath its crust.
“GJ 9827d could be half water and half rock,” explained Björn Benneke of the University of Montreal, who co-led the research. “There would be a lot of water vapor on smaller lumps of rock.”
“So far we have not been able to directly detect the atmosphere of such a small planet. And we are getting there gradually,” he added.
For three years, Hubble was able to analyze the wavelengths of colors in GJ 9827d's atmosphere as the light from the star around which it orbited was filtered through its atmosphere, and detect the presence of water molecules.
Although this planet has a water-rich atmosphere, its temperature of 425°C makes it uninhabitable.
However, this discovery paves the way for further studies of GJ 9827d and similar planets, particularly using the James Webb Space Telescope, which can use its high-resolution infrared images to search for other atmospheric molecules such as carbon dioxide and methane.