As of: January 30, 2024, 11:05 a.m
By: Lennart Schwenck
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A milestone in space research: Hubble discovers the smallest exoplanet with water vapor.
This stimulates research into the atmospheres again.
Washington, DC - Astronomers using the NASA/ESA Hubble Space Telescope have discovered the smallest exoplanet where water vapor has been detected in the atmosphere.
The European Space Agency (ESA) announced this in a press release on Friday (January 26).
The planet “GJ 9827d”, about twice the diameter of Earth, could serve as a model for water-rich atmospheres on planets in our galaxy.
“This would be the first time that we can directly show through atmospheric detection that these planets with water-rich atmospheres can actually exist around other stars,” said team member Björn Benneke from the Université de Montréal.
“This is an important step in determining the occurrence and diversity of atmospheres on rocky planets.”
Hubble's discovery opens the door for a closer study of the planet.
It is a good target for the NASA/ESA/CSA James Webb Space Telescope to search for other atmospheric molecules using infrared spectroscopy.
© Imago Images
Mysterious Atmosphere: The Search for Water Vapor and Remnants on GJ 9827d
It remains unclear for now whether Hubble spectroscopically measured low levels of water vapor in a dense, hydrogen-rich atmosphere.
It is also possible that the planet's atmosphere consists mostly of water left behind after an original hydrogen/helium atmosphere was vaporized by the star's radiation.
“Our observation program was specifically developed with the aim of not only detecting the molecules in the planet's atmosphere, but also specifically searching for water vapor.
“Both results would be exciting, regardless of whether water vapor is dominant or just a tiny species in a hydrogen-dominated atmosphere,” said lead author of the paper, Pierre-Alexis Roy of the Université de Montréal.
A look into the future: The challenges of atmospheric research on small exoplanets
“So far we have not been able to directly detect the atmosphere of such a small planet.
And we are now slowly getting into this area,” Benneke added.
“At some point, as we study smaller planets, there must be a transition where these small worlds no longer have hydrogen and have atmospheres more like Venus (which is dominated by carbon dioxide).”
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With a temperature of around 425 degrees Celsius, the planet would be a hostile, steamy world if its atmosphere consisted primarily of water vapor, similar to the conditions on Venus.
The mini planet GJ 9827d:
GJ 9827d was discovered in 2017 by NASA's Kepler Space Telescope.
It completes an orbit around a red dwarf star every 6.2 days.
The star GJ 9827 is located 97 light-years from Earth in the constellation Pisces.
Two future scenarios for GJ 9827d: A mini-Neptune or a water-rich rocky planet?
The research team currently has two scenarios open to them: Either the planet retains its hydrogen-rich shell, making it a mini-Neptune, or it could be a warmer version of Jupiter's moon Europa, with a crust-covered water mass twice as large as on Earth .
Björn explains: “GJ 9827d could be a mixture of water and rock, with potential water vapor on a smaller, rocky body.”
If GJ 9827d has a residual water-rich atmosphere, this suggests that it formed further away from its host star, where it is colder and water is present in the form of ice.
As it moved closer to the star, it received more radiation, causing the hydrogen to heat up and possibly escape.
The alternative theory is that the planet was formed near the hot star, with a trace of water in its atmosphere.
In May 2023, the James Webb telescope made similar headlines when it also discovered water vapor on the exoplanet GJ 486 b.
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