Hubble finds water vapor in the atmosphere of a small exoplanet

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Astronomers using the Hubble Space Telescope have discovered water molecules in the atmosphere of a small, extremely hot exoplanet 97 light-years from Earth.

The planet, called GJ 9827d, is about twice the diameter of Earth, and is the smallest exoplanet found to have water vapor in its atmosphere, according to a new study.

Water is essential for life as we know it, but the planet is unlikely to host any kind of life due to high temperatures that would turn the water-rich atmosphere into scorching steam.

Astronomers have yet to uncover the true nature of this unusual world's atmosphere, but this discovery paves the way for further research in their quest to understand the origins of planets outside our solar system.

The findings appeared in a report published Thursday in Astrophysical Journal Letters.

“Water on a planet this small is a historic discovery,” study co-author Laura Kreidberg, managing director of the Division of Exoplanetary Atmospheric Physics at the Max Planck Institute for Astronomy in Heidelberg, Germany, said in a statement. “It comes closer than ever to characterizing truly Earth-like worlds.”

However, the planet's temperature reaches 800°F (427°C), making it a steamy, inhospitable and hot world like Venus.

“This will be the first time we can directly show through atmospheric detection that these planets with water-rich atmospheres can actually exist around other stars,” said study co-author Björn Beneke, a professor at the University of Montreal's Trottier Research Institute. Exoplanets, in a statement. “This is an important step toward determining the prevalence and diversity of atmospheres on rocky planets.”

Currently, the research team cannot tell whether Hubble has captured traces of water vapor within a puffy, hydrogen-rich atmosphere or whether the planet has a water-rich atmosphere because the host star evaporated GJ 9827d's original hydrogen-helium atmosphere.

“Our observing program, led by principal investigator Ian Crosfield of (University of Kansas) in Lawrence, Kansas, was specifically designed with the goal of not only detecting molecules in the planet's atmosphere, but also actually looking for water vapor specifically.” “Either outcome would be exciting, whether water vapor is dominant or just a small species in a hydrogen-dominated atmosphere,” lead study author Pierre-Alexis Roy, a doctoral student at the Trottier Institute at the University of Montreal, said in a statement.

NASA's Kepler mission first discovered the planet orbiting a red dwarf star in the constellation Pisces in 2017. The exoplanet completes one orbit around its host star every 6.2 days.

Astronomers observed planet GJ 9827d during 11 transits, or the times the planet crossed in front of its star during orbit, over a period of three years. Filtering starlight through the planet's atmosphere helped astronomers measure the signature of water molecules.

“Until now, we have not been able to directly detect the atmosphere of a small planet like this. We are slowly getting into this system now,” Beinecke said. “At some point, as we study small planets, there has to be a transition where there is no more hydrogen.” “On these small worlds, they have an atmosphere similar to that of Venus (dominated by carbon dioxide).”

Understanding more about the planet's atmosphere could help astronomers classify exactly what type of world GJ 9827d is. Currently, the team has two possible theories.

The planet is likely a mini-Neptune, with a hydrogen-rich atmosphere and water vapor. If so, GJ 9827d likely formed at a greater distance from its host star than its current location, meaning the planet would have been cooler and water would have been present in the form of ice (similar to Neptune and Uranus, the more distant planets in our solar system). .

As the planet approached its star and was exposed to more stellar radiation, the hydrogen heated up and escaped, or is still escaping, according to the researchers.

Or astronomers suspect that GJ 9827d may be a warmer version of Jupiter's icy moon Europa, which has an ocean beneath a thick icy crust. Beneke said the planet may be half water and half rock.

Water is one of the most common molecules found throughout the universe, and for many years, astronomers have included the discovery of water as a larger part of the search for extraterrestrial life.

“Observing water is a gateway to finding other things,” study co-author Thomas Green, an astrophysicist at NASA's Ames Research Center in Silicon Valley, California, said in a statement. “This Hubble discovery opens the door for future study of these types of planets with the James Webb Space Telescope. With additional infrared observations, the James Webb Space Telescope can see much more, including carbon-bearing molecules such as carbon monoxide, carbon dioxide and methane. Once we have a total inventory of a planet's elements, we can compare them to the star it orbits and understand how it formed.

Astronomers have already observed GJ 9827d using the Webb telescope to look for water and other types of molecules, and that data will be shared in the future.

“We can't wait to see what this data reveals,” Kreidberg said. “We hope that we can now settle the matter of the Water Realms once and for all.”