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James Webb telescope finds water around a comet in the main asteroid belt

The discovery also creates a new mystery.

NASA, ESA

The James Webb Space Telescope just made its second breakthrough observation in as many weeks. Researchers have used the observatory's near-infrared camera to detect the first known instance of water vapor around a comet in the main asteroid belt, also known as a main belt comet. Scientists had thought comets could preserve water ice so relatively close to the Sun, but didn't have firm evidence until now. They generally expected comets to sit in the Kuiper Belt or Oort Cloud, both of which are far enough away from the Sun that ice could last.

The findings have created a new riddle, however. While carbon dioxide normally represents 10 percent of the potentially vaporized material in a comet, Webb's instruments didn't detect any in Read. The research group speculates that the CO2 either dissipated over billions of years, or that Read formed in a comparatively balmy part of the Solar System that didn't have CO2.

Read was one of the first bodies used to establish the main belt comet category. The Webb telescope is the first equipment powerful enough to study these comets in detail.

More observations will be needed to understand if Read's lack of CO2 is a fluke or shared by other main belt comets. Whether it is or not, team member Stefanie Milam suggests a sample collection mission might be helpful in learning more about comets like this. It would certainly be more practical than other missions — the Kuiper Belt starts roughly at the edge of Neptune's orbit, while the Oort Cloud is roughly two light-years away.