NASA’s James Webb Space Telescope has made another long-sought scientific breakthrough possible, this time for solar system scientists studying the origins of Earth’s abundant water. Using Webb’s NIRSpec (Near-Infrared Spectrograph) instrument, astronomers have confirmed for the first time gas specifically, water vapor around a comet in the main asteroid belt, suggesting that water ice from the primordial solar system may be preserved in the region.
However, the successful detection of water comes with a new conundrum: unlike other comets, comet 238P/Read had no detectable carbon dioxide.
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,” said Stefanie Milam, Webb associate scientist for planetary science. and co-author of the study reporting the finding.
“Understanding the history of water distribution in the Solar System will help us understand other planetary systems and whether they might be on their way to host Earth-like planets,” she added.
Comet Read is a main-belt comet an object that resides in the main asteroid belt but that regularly displays a comet-like halo, or coma, and tail. Main belt comets are themselves a fairly new classification, and Comet Read was one of the original three comets used to establish the category.
Previously, comets were understood to reside in the Kuiper belt and Oort cloud, beyond the orbit of Neptune, where their ices could be preserved further from the Sun. The frozen material that evaporates as they approach the Sun gives comets their characteristic coma and streaming tail, distinguishing them from asteroids.
Scientists have long speculated that water ice might be preserved in the warmer asteroid belt, inside Jupiter’s orbit, but definitive proof was elusive—until Webb.
“In the past we have seen objects in the main belt with all the characteristics of comets, but only with these precise spectral data from Webb can we say yes, it is definitely water ice that is creating this effect,” explained astronomer Michael Kelley. from the University of Maryland, lead author of the study.
“With Webb’s observations of Comet Read, we can now show that water ice from the early solar system can be preserved in the asteroid belt,” Kelley said.
The bigger surprise was the lack of carbon dioxide. Carbon dioxide typically makes up about 10 percent of the volatile material in a comet, which can be easily vaporized by the sun’s heat. The scientific team presents two possible explanations for the lack of carbon dioxide. One possibility is that Comet Read had carbon dioxide when it formed, but lost it due to high temperatures.
“Being in the asteroid belt for a long time could do that carbon dioxide evaporates more easily than water ice and could seep out for billions of years,” Kelley said. Alternatively, he says, Comet Read may have formed in a particularly warm pocket of the solar system where no carbon dioxide was available.
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