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Astronomers using the Hubble Space Telescope have detected water molecules in the atmosphere of a small, blazing-hot exoplanet 97 light-years from Earth.
The planet, named 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 to life as we know it, but the planet is unlikely to host any form of life due to searing temperatures that would turn a water-rich atmosphere into scorching steam.
Astronomers have yet to discover the true nature of this world’s unusual atmosphere, but the revelation paves the way for further investigation as they try to understand the origins of planets outside our solar system.
The results appeared in a report published Thursday in The Astrophysical Journal Letters.
“Water on such a small planet is a remarkable discovery,” study author Laura Kreidberg, managing director of the exoplanet atmospheric physics department at the Max Planck Institute for Astronomy in Heidelberg, Germany, said in a statement. “It gets closer than ever to characterizing Earth-like worlds.”
But the planet reaches temperatures of 800 degrees Fahrenheit (427 degrees Celsius), making it a steamy, unheated world as hot as Venus.
“This was the first time we can show directly through atmospheric detection, that these planets with water-rich atmospheres can actually exist around other stars,” said study coauthor Björn Benneke, professor at the Trottier Research Institute of the University of Montreal. Exoplanets, in a statement. “This is an important step in determining the prevalence and diversity of atmospheres on the rocky planets.”
Currently, the research team cannot say whether Hubble picked up traces of water vapor within a puffy, hydrogen-rich atmosphere or whether the planet has a water-rich atmosphere because the host star has evaporated an underlying atmosphere of hydrogen and helium. GJ 9827d.
“Our observing program, led by principal investigator Ian Crossfield from (the University of Kansas) in Lawrence, Kansas, was specifically designed with the goal of not only detecting the molecules in the planet’s atmosphere, but specifically looking at water vapor,” said the t -lead study author Pierre-Alexis Roy, a doctoral student at the University of Montreal’s Trottier Institute, said in a statement. “Either result would be exciting, whether there is water vapor dominant or just a tiny species in a hydrogen dominant atmosphere.”
A planetary conflict
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 GJ 9827d during 11 transits, or times when the planet crossed in front of its star during its orbit, over three years. Starlight filtering 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 such a small planet. And we’re slowly getting into this regime now,” Benneke said. “At some point, as we study the smaller planets, there has to be a transition where these small worlds no longer have hydrogen, and have atmospheres more like Venus (which has dioxide carbon ahead of them).
A greater understanding of the planet’s atmosphere could help astronomers classify exactly what kind of world GJ 9827d is. Currently, the team has two possible theories.
The planet may be a mini-Neptune with a hydrogen-rich atmosphere containing water vapor. If so, it is likely that GJ 9827d formed further from its host star than its current location, meaning that the planet was colder and that water was present in the form of ice (like Neptune and Uranus, the most distant planets in our solar system) .
As the planet migrated closer to its star and was blasted with more intense radiation, the hydrogen heated up and escaped, or is still escaping, according to the researchers.
Alternatively, astronomers suspect that GJ 9827d could be a warmer version of Jupiter’s icy moon Europa, which has an ocean under a thick icy crust. The planet could be half water and half rock, Benneke said.
The search for water in space
Water is one of the most common molecules found throughout the universe, and for many years, astronomers have included the detection of water as a larger part of the search for life beyond Earth.
“Looking at water is a way to find other things,” study author Thomas Greene, an astrophysicist at NASA’s Ames Research Center in Silicon Valley, California, said in a statement. “This Hubble discovery opens the door to future study of these types of planets by the James Webb Space Telescope. JWST can see much more with additional infrared observations, including carbon molecules such as carbon monoxide, carbon dioxide, and methane. Once we get a complete inventory of the planet’s elements, we can compare those to the star it orbits and understand how it formed.”
Astronomers have already observed GJ 9827d with the Webb telescope to search for water and other types of molecules, and that data will be shared in the future.
“We can hardly wait to see what that data reveals,” Kreidberg said. “I hope we can solve the issue of water worlds once and for all.”
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