Hubble Uncovers Water Vapor in Small Exoplanet’s Atmosphere | NASA Goddard

Hubble Uncovers Water Vapor in Small Exoplanet’s Atmosphere | NASA Goddard

Astronomers using NASA’s Hubble Space Telescope have observed water vapor in the atmosphere of the smallest exoplanet ever detected. Located 97 light-years away, planet GJ 9827d is approximately twice the size of Earth. 

This finding raises the possibility of other planets with water-rich atmospheres in our galaxy. However, it remains uncertain whether the observed water vapor is in a hydrogen-rich atmosphere or if the planet's atmosphere is predominantly water.

Water on a planet this small is a landmark discovery, pushing us closer than ever to characterizing truly Earth-like worlds, and thanks to the Hubble Space Telescope we will be able to continue our search for more planets like our own.

Because the planet is as hot as Venus at roughly 425 degrees Celsius, it definitely would be an inhospitable, steamy world if the atmosphere were predominantly water vapor.

Science paper: 

https://esahubble.org/static/science_papers/heic2312/heic2312.pdf

At present the team is left with two possibilities. The planet is still clinging to a hydrogen-rich envelope laced with water, making it a mini-Neptune. Alternatively, it could be a warmer version of Jupiter’s moon Europa, which has twice as much water as Earth beneath its crust.

If the planet has a residual water-rich atmosphere, then it must have formed farther away from its host star, where the temperature is cold and water is available in the form of ice, than its present location. In this scenario, the planet would have then migrated closer to the star and received more radiation. The hydrogen was then heated and escaped, or is still in the process of escaping, the planet’s weak gravity. The alternative theory is that the planet formed close to the hot star, with a trace of water in its atmosphere.

The Hubble program observed the planet during 11 transits—events in which the planet crossed in front of its star—that were spaced out over three years. During transits, starlight is filtered through the planet’s atmosphere and carries the spectral fingerprint of water molecules. If there are clouds on the planet, they are low enough in the atmosphere that they do not completely hide Hubble’s view of the atmosphere, and Hubble is able to probe water vapor above the clouds.

Hubble’s discovery opens the door to studying the planet in more detail. It is a good target for the James Webb Space Telescope to do infrared spectroscopy to look for other atmospheric molecules.

GJ 9827d was discovered by NASA’s Kepler Space Telescope in 2017. It completes an orbit around a red dwarf star every 6.2 days. The star, GJ 9827, lies 97 light-years from Earth in the constellation Pisces.

Credit: NASA's Goddard Space Flight Center (GSFC)

Paul Morris: Lead Producer 

Cassandra Morris: Voiceover

Duration: 2 minutes

Release Date: Jan. 25, 2024

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