File:Comet Spectra Comparison (2023-123).jpg

English: 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.

Though it is only one example, the water detection in Comet Read is evidence that water from the early solar system can be preserved in the asteroid belt, where it is much warmer than the more distant regions where most comets reside. Comet Read had more in store for scientists, though, when further down the spectrum Comet Read did not show the characteristic, expected bump indicating the presence of carbon dioxide. Comet Hartley 2’s spectrum provides an example of what was anticipated. Carbon dioxide is typically 10 percent of the material in a comet that sublimates near the Sun, producing the characteristic coma and tail of a comet.

Future Webb observations of main belt comets will be necessary to begin understanding whether Comet Read is unique in its lack of carbon dioxide, or if this is a previously-unknown feature of comets in the asteroid belt.