The US Space Agency (NASA) and the European Space Agency (ESA) announced Thursday that the Hubble Space Telescope has discovered water vapor in the atmosphere of the smallest known planet outside the solar system.

The presence of “water on such a small planet is a remarkable discovery,” said study co-director Laura Kreidberg, of the Max Planck Institute for Astronomy in Germany.

He considered that “this brings us closer and closer to discovering worlds that truly resemble Earth.”

The planet in question, GJ 9827d, which has a diameter almost twice that of Earth, is located in the constellation Pisces, 97 light-years away, or more than 900 thousand billion kilometers, according to a press release by the agencies.

NASA and the European Space Agency say the planet is a “mini-Neptune,” with a hydrogen-rich, water-filled atmosphere, or a hotter version of Jupiter’s moon Europa, which contains twice as much water as Earth does under its crust.

“GJ 9827d may be half water and half rock. There will be a lot of water vapor on small pieces of rock. Until now, we have not been able to detect it directly in the atmosphere,” explained Björn Beneke, from the University of Montreal, who also co-led the research. “The atmosphere is for such a small planet, but we're getting there slowly.”

For three years, Hubble analyzed the wavelengths of colors in GJ 9827d's atmosphere, as light from the orbiting star was filtered through its atmosphere to detect the presence of water molecules.

Although this planet has an atmosphere rich in water, its temperature of 425 degrees Celsius makes it uninhabitable.

However, this discovery paves the way for other studies of GJ 9827 and similar planets, particularly through the James Webb Space Telescope, which can use high-resolution infrared images to look for other atmospheric molecules, such as carbon dioxide and methane.