2023-05-15 18:00:00
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NASA’s James Webb Space Telescope has enabled another long-awaited scientific breakthrough, this time for solar system scientists studying the origins of Earth’s abundance of water. Using Webb’s Near Infrared Spectrograph (NIRSpec) instrument, astronomers have confirmed for the first time the existence of gas—specifically, water vapor—around a comet in the main asteroid belt. indicating that water ice from the primordial solar system may be preserved in that region. However, with the successful detection of water comes a new puzzle: Unlike other comets, Comet 238P/Read had no detectable carbon dioxide.
“Our water-soaked world, teeming with life and, as far as we know, unique in the universe, is somewhat of a mystery: We’re not sure where all this water came from,” said Stefanie Milam, Webb Telescope Associate Project 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 hosting an Earth-like planet,” she added.
Comet Read is a main-belt comet, an object that resides in the main asteroid belt but periodically displays a halo, or coma, and a comet-like tail. The main belt comets themselves are a fairly new classification, and Comet Read was one of the original three comets used to establish this category. Before then, comets were understood to reside in the Kuiper belt and Oort cloud, beyond Neptune’s orbit, where their ices might be preserved farther from the Sun. Frozen material vaporizing as It is the fact that comets are approaching the Sun that gives these objects their characteristic coma and floating tail, differentiating them from asteroids. Scientists have long speculated that water ice might be preserved in the warmer asteroid belt, within Jupiter’s orbit, but definitive proof was difficult to come by, until the arrival of the Webb telescope.
This illustration of Comet 238P/Read shows the comet’s sublimation in the main belt: its water ice vaporizes as its orbit approaches the Sun. This is significant, as sublimation is what distinguishes comets from comets. asteroids and creates their characteristic tail and nebulous halo, or coma. The detection of water vapor in Comet Read by the James Webb Space Telescope is an important landmark in the study of main-belt comets and in the broader investigation of the origin of Earth’s abundant water.
Credits: NASA, ESA
“In the past, we have seen main belt objects that have all the characteristics of comets, but only with these precise spectral data from Webb can we say that yes, it is definitely water ice that is creating that effect,” explained astronomer Michael Kelley, of the University of Maryland, lead author of the study.
“With the Webb telescope observations of Comet Read, we can now show that water ice from the early Solar System may be preserved in the asteroid belt,” Kelley said.
The absence of carbon dioxide was a bigger surprise. Typically, carbon dioxide makes up about 10 percent of a comet’s volatile material that can easily be vaporized in the Sun’s heat. The science team offers two possible explanations for the lack of carbon dioxide. 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 could cause this: Carbon dioxide vaporizes more easily than water ice and would have seeped in for billions of years,” Kelley said. Another option, she said, is that Comet Read would have formed in a particularly hot pocket of the solar system, where carbon dioxide was not available.
This image of Comet 238P/Read was taken with the Near Infrared Camera (NIRCam) instrument aboard NASA’s James Webb Space Telescope on September 8, 2022. It shows the hazy halo, called the coma, and the tail, which are characteristic of comets, unlike asteroids. The coma and dust tail are the result of vaporization of the ice as the Sun heats the main body of the comet.
Credits: NASA, ESA, CSA, M. Kelley (University of Maryland). Image processing: H. Hsieh (Planetary Sciences Institute), A. Pagan (STScI)
The next step is to take the investigation beyond Comet Read to see how it compares to other main-belt comets, says astronomer Heidi Hammel of the Association of Universities for Research in Astronomy (AURA). head of Webb’s Guaranteed Time Observations program for solar system objects and co-author of the study. “These asteroid belt objects are small and faint, 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’s going to be exciting to find out,” Hammel said.
Co-author Milam envisions the possibilities of bringing research even closer to our planet. “Now that Webb has confirmed that there is preserved water as close as the asteroid belt, it would be exciting to follow up on this discovery with a sample-collection mission and learn what else main-belt comets can tell us.”
The study was published in the journal Nature.
The James Webb Space Telescope is the world’s premier space science observatory. Webb will solve the mysteries of our solar system, see beyond distant worlds around other stars, and explore the mysterious structures and origins of our universe and our place in it. Webb is an international program run by NASA with its partners: ESA (European Space Agency) and the Canadian Space Agency (CSA).
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