Webb finds water, and a new mystery, in a rare main belt comet
(Nanowerk News) NASA’s James Webb Space Telescope has enabled another long-sought scientific breakthrough, 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 gas – specifically water vapor – around comets in the main asteroid belt for the first time, suggesting that water ice from the ancient solar system could be preserved in the region. However, the success of water detection came with a new conundrum: unlike other comets, Comet 238P/Read had no detectable carbon dioxide.
“Our water-filled 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’s deputy project scientist for planetary science and co-author. in the study that reported the finding (“Spectroscopic identification of water emission from main belt comets”). “Understanding the history of water distribution in the solar system will help us understand other planetary systems, and if they could host Earth-like planets,” he added.
Comet Read is a main belt comet – an object that is in the main asteroid belt but periodically displays a halo, or coma, and a comet-like tail. Main belt comets are themselves a fairly new classification, and Comet Read was one of the three original comets used to define the category. Prior to that, comets were known to reside in the Kuiper Belt and Oort Cloud, beyond the orbit of Neptune, where their ice could be preserved farther from the Sun. This frozen material that vaporizes as it approaches the Sun is what gives comets the characteristic flowing coma and tail that distinguishes them from asteroids. Scientists have long speculated that water ice could be preserved in the warmer asteroid belt, within Jupiter’s orbit, but definitive proof has been elusive – until Webb.
“In the past, we have seen objects in the main belt with all the characteristics of comets, but only with this precise spectral data from Webb can we say yes, it must be water ice creating that effect,” explained astronomer Michael Kelley. from the University of Maryland, the study’s lead author.
“With Webb’s observations of Comet Read, we can now show that water ice from the early solar system could be preserved in the asteroid belt,” said Kelley.
The missing carbon dioxide was an even bigger surprise. Typically, carbon dioxide makes up about 10 percent of the volatile matter in comets that can be easily vaporized by the sun’s heat. The science team presents two possible explanations for the carbon dioxide deficiency. One possibility is that Comet Read had carbon dioxide when it formed but has lost it due to warm temperatures.
“Being in the asteroid belt for a long time can do the trick – carbon dioxide evaporates more easily than water ice, and can seep out over billions of years,” Kelley said. Or, he says, Comet Read might have formed in a very warm pocket of the solar system, where there was no available carbon dioxide.
The next step is to take research beyond Comet Read to see how other main belt comets compare, said astronomer Heidi Hammel of the Association of Universities for Research in Astronomy (AURA), lead Webb’s Guaranteed Time Observations of solar system objects and study co-author. “These objects in the asteroid belt are small and dim, and with Webb we can finally see what is happening to them and draw some conclusions. Do other main belt comets also lack carbon dioxide? Either way, it would be nice to know,” said Hammel.
Milam’s co-author envisions the possibility of bringing the research closer to home. “Now that Webb has confirmed that water is preserved as close to the asteroid belt, it will be very exciting to follow up this discovery with a sample collection mission, and learn what else main belt comets can tell us.”
