File:NASA’s Webb Finds Water, and a New Mystery, in Rare Main Belt Comet (52940498828).jpg

Webb confirmed the first detection of water vapor around a rare type of comet in the main asteroid belt. This suggests that water from the early solar system can be preserved in that region as ice — a breakthrough for studying the origins of water on Earth.

The comet, Comet Read, is called a main belt comet. This is a fairly new classification, and Comet Read was actually one of the original 3 comets to establish this category. Unlike most comets, found beyond the orbit of Neptune in the Kuiper Belt or the Oort Cloud, main belt comets reside in the asteroid belt between Mars and Jupiter. And unlike asteroids, they periodically display a halo and tail.

Comets get their distinctive halos and tails from frozen material vaporizing as they approach the Sun. Although comet-like objects were previously seen in the main belt, Webb has brought us the first definitive proof that water ice is creating that effect.

The successful detection of water came with another puzzle: Comet Read had no detectable carbon dioxide. (Carbon dioxide usually makes up 10% of a comet's volatile material.) Scientists theorize its carbon dioxide got lost over time due to the main belt's relatively warm temperatures, or it formed in an area where no carbon dioxide was available.

We don’t quite know how water got to Earth. According to the science team, understanding the history of water distribution in our solar system will in turn help us understand other planetary systems — and if they could be on their way to hosting an Earth-like planet.

Read more about these findings: go.nasa.gov/3W8Nd02

In this image: This graphic presentation of spectral data highlights a key similarity and difference between observations of Comet 238P/Read by the NIRSpec (Near-Infrared Spectrograph) instrument on NASA’s James Webb Space Telescope in 2022 and observations of Comet 103P/Hartley 2 by NASA’s Deep Impact mission in 2010. Both show a distinct peak in the region of the spectrum associated with water. Finding this in Comet Read was a significant accomplishment for Webb, as it is in a different class of comets than Jupiter-family comets like Hartley 2, and this marks the first time that a gas has been confirmed in such a main belt comet. However, Comet Read did not show the characteristic, expected bump indicating the presence of carbon dioxide. Credits: NASA, ESA, CSA, and J. Olmsted (STScI)