In historic first, James Webb detects water surrounding a rare comet

The new observations provide further evidence that Earth's water was delivered by ancient space rocks.
Chris Young
An artist's impression of Comet 238P/Read.
An artist's impression of Comet 238P/Read.


The James Webb Space Telescope detected water around a rare comet in the main asteroid belt located between Jupiter and Mars.

The new observation marks another scientific breakthrough for Webb as it is the first time gas — here in the form of water vapor — has been observed surrounding a main belt asteroid.

The new discovery suggests that water may have been preserved as ice in the main asteroid belt during the early evolution of the Solar System.

Webb detects water around main asteroid belt comet

Scientists believe the space rock, called Comet 238P/Read, could provide key evidence for theories that suggest water was delivered to Earth by comets and asteroids.

"In the past, we've seen objects in the main belt with all the characteristics of comets, but only with this precise spectral data from the JWST can we say 'yes,' it's definitely water ice that is creating that effect," University of Maryland astronomer Michael Kelley, who led this research, explained in a press statement.

"With the JWST's observations of Comet Read, we can now demonstrate that water ice from the early solar system can be preserved in the asteroid belt," Kelley continued.

In historic first, James Webb detects water surrounding a rare comet
Comet 238P/Read captured by Webb's NIRCam (Near-Infrared Camera) instrument.

The observation, detailed in a new paper in the journal Nature, did also throw up another unexpected surprise. Though astronomers expected to detect carbon dioxide around Comet 238P/Read, none was present, and they aren't completely sure why — CO2 makes up roughly 10 percent of the volatile matter in comets.

"Being in the asteroid belt for a long time could do it  —  carbon dioxide vaporizes more easily than water ice and could percolate out over billions of years," Kelley said. Alternatively, the comet may have formed in a part of the Solar System devoid of CO2.

James Webb can help us better understand our "water-soaked world"

The new observation is another feather in the James Webb team's cap as it constitutes the first time gas has ever been confirmed in a main-belt comet. As opposed to asteroids, which are made of rocky material, comets are composed of ice and dust and are typically found in the far reaches of the Solar System.

However, astronomers have recently discovered comets relatively nearby in the main asteroid belt, making them a prime target for Webb.

"Our water-soaked world, teeming with life and unique in the universe as far as we know, is something of a mystery  —  we're not sure how all this water got here," research co-author and Webb Deputy Project Scientist for Planetary Science Stefanie Milam explained in the statement. "Understanding the history of water distribution in the solar system will help us to understand other planetary systems and if they could be on their way to hosting an Earth-like planet."

Next, the team aims to look beyond Comet 238P/Read to determine whether other comets have similar compositions. Webb, meanwhile, will continue to uncover the mysteries of the cosmos and shed new light on distant phenomena — such as the first asteroid belt observed beyond our solar system — that will help us better understand our place in the universe.

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