Using the Hubble Space Telescope, astronomers have discovered that the atmosphere of a relatively small planet outside the solar system is rich in water vapor. However, don’t plan a holiday to this destination yet. The planet’s surface is hot enough to melt lead, meaning it’s a steamy world inhospitable to life as we know it.
More specifically, the team behind this finding says that the extra-solar planet, or exoplanet, called GJ 9872d, exhibits Venus-like temperatures of 752 degrees Fahrenheit (400 degrees Celsius). But that doesn’t make this discovery any less exciting.
Although scientists have previously found water vapor in the atmospheres of many extrasolar planets, the Hubble Telescope observations of this hot and steamy world, called GJ 9827d, represent the smallest exoplanet around which this essential element for life has been found to date found it.
“The discovery of water on GJ 9827d is exciting because it is the smallest planet so far where we have detected an atmosphere,” Laura Kreidberg, team member and director of the Atmospheric Physics of Exoplanets department at the Max Planck Institute for Astronomy, told Space.com. “It comes closer than ever to characterizing truly Earth-like worlds.”
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GJ 9827d is about twice as wide as Earth and orbits a star called GJ 987, which is about 97 light-years away from us in the direction of the constellation Pisces. The planet is just one of three Earth-like worlds orbiting this star, which appears to be about 6 billion years old.
“This would be the first time that we can directly demonstrate through atmospheric detection that these planets with water-rich atmospheres can actually exist around other stars,” says Björn Benneke, team member and scientist at the Trottier Institute for Research on Exoplanets at the Université. de Montreal, said in a statement. “This is an important step toward determining the prevalence and diversity of atmospheres on rocky planets.”
However, an important question remains: what kind of planet is GJ 9872d?
“The nature of these small planets, between two and three times the size of Earth, is really uncertain,” Kreidberg said. “They could be true super-Earths, with a large rocky core and a light atmosphere on top, or they could be something completely different, like a water world composed mainly of water ice that has no analogue in our own solar system.”
Water world or hydrogen-rich mini-Neptune?
Hubble observed GJ 9827d for three years and watched as the world passed by, or passed through, the side of its star eleven times. Because chemical elements and compounds absorb light at characteristic wavelengths, a parent star’s light passing through a planet’s atmosphere carries fingerprints of the elements that make up the planet itself.
Currently, the astronomers behind this discovery are unsure whether Hubble detected a small amount of water in a puffy, hydrogen-rich atmosphere when it examined GJ 9872d – or whether the planet’s atmosphere is mostly water.
“Both results would be exciting whether water vapor is dominant or just a minor species in a hydrogen-dominant atmosphere,” said Pierre-Alexis Roy, lead researcher and scientist at the Trottier Institute for Research on Exoplanets at the Université de Montréal. in the statement.
If GJ 9872d spent its 6-billion-year life close to its parent star, intense radiation would have boiled away any primordial hydrogen present, leaving the small planet with an atmosphere dominated by water vapor. This seems to be supported by the fact that attempts to detect hydrogen around GJ 9872d have so far failed.
Alternatively, if GJ 9872d is still clinging to a hydrogen-rich envelope laced with water, it would be classified as a mini-Neptune, a type of planet that is less massive than Neptune but still resembles the solar system’s ice giant because it has a thick atmosphere. of hydrogen and helium.
On the other hand, the exoplanet could resemble a larger and hotter version of Jupiter’s moon Europa, which is believed to harbor twice as much water as Earth, sealed under a thick crust of ice. “The planet GJ 9827d could be half water and half rock. And there would be a lot of water vapor on top of a smaller rocky body,” Benneke said.
If GJ 9827d still has a thick atmosphere of water vapor, this would mean it was born further away from its star – where temperatures would have been lower – before migrating to the position we see today.
This migration would have resulted in the exoplanet being irradiated with more radiation from its parent star, potentially converting ice on GJ 9827d into liquid water and water vapor. Any hydrogen present would have heated up and eventually leaked from the planet’s atmosphere due to Earth’s relatively low gravity; this leakage could still be happening as astronomers observe the exoplanet today.
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“Until now we had not been able to directly detect the atmosphere of such a small planet. And now we are slowly entering this regime,” Benneke added. “At some point, as we study smaller planets, there should be a transition where there is no more hydrogen on these small worlds, and they have an atmosphere more like that of Venus, which is dominated by carbon dioxide.”
The study of GJ 9827d with Hubble has marked the planet as a prime target for a follow-up survey conducted with the James Webb Space Telescope (JWST). This work is already underway and the $10 billion telescope could reveal more details about this potential water world.
“GJ 9827d is being observed with JWST to learn more about the composition of the atmosphere and to look for additional molecules such as carbon dioxide,” Kreidberg concluded. “The sightings are ongoing and we will have more answers soon!
“Hopefully we can now settle the issue of the water worlds once and for all.”
The team’s research was published last year in The Astrophysical Journal Letters.