A story of two detections is the most recent finding made by the James Webb Space Telescope.
When solar system researchers went on an asteroid belt treasure hunt using NASA's James Webb Space Telescope, what they didn't uncover turned out to be just as important as what they found. If a spectrum of potential chemical compounds serves as a guide for what to search for, the presence of water vapor on Comet Read is indicated by the symbol X, providing a long-sought solution to the question of how liquid water on Earth, and subsequently life, originally formed. However, although being present in all other comets, carbon dioxide was absent from the chart. Therefore, in addition to continuing their research into the origins of ancient water in the solar system, scientists will also be looking for solutions in the nearby universe to an unexpected new question.
Illustration showing the intricate, cratered surface of a comet's stony, potato-shaped mass in close-up. Glowing rays show water ice being vaporized by the heat of the Sun and are projected from the stony surface like sunshine through clouds.
Another long-awaited scientific discovery has now been made thanks to NASA's James Webb Space Telescope, this time by solar system researchers looking into the origins of Earth's copious water. Astronomers have discovered gas - especially water vapor - surrounding a comet in the main asteroid belt for the first time using Webb's NIRSpec (Near-Infrared Spectrograph) instrument, proving that water ice from the early solar system may be maintained there. The discovery of water, however, raises a brand-new conundrum: Comet 238P/Read contained no measurable carbon dioxide, unlike previous comets.
"Our water-soaked world, teeming with life and, as far as we know, unique in the universe, is something of a mystery - we're not sure how all this water got here," said Stefanie Milam, Webb deputy project scientist for planetary science and a co-author on the article describing the finding. We can better comprehend other planetary systems and determine if they may eventually include an Earth-like planet by understanding the history of water distribution in the solar system, she continued.
A main-belt comet is an object that lies in the main asteroid belt but that sometimes exhibits a halo or coma, and tail like a comet. Comet Read is one such object. Comet Read was one of the initial three comets used to define the category of main belt comets, which is itself a relatively recent categorization. Prior to then, it was thought that comets lived in the Kuiper Belt and Oort Cloud, past Neptune's orbit, where their ice could be kept further from the Sun. Comets are distinguished from asteroids by their unique coma and streaming tails, which are caused by frozen material that vaporizes when they approach the Sun. Prior to Webb, concrete evidence for the long-held theory that water ice may be retained in the warmer asteroid belt within Jupiter's orbit remained elusive.
"In the past, we've 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's definitely water ice that is creating that effect," said the lead author of the study Michael Kelley of the University of Maryland.
We can now show that water ice from the early solar system can be retained in the asteroid belt, Kelley added, thanks to Webb's studies of Comet Read.
More shockingly, carbon dioxide was lacking. About 10% of a comet's volatile material, which is easily vaporized by the Sun's heat, is typically carbon dioxide. The scientific team offers two theories for why there isn't any carbon dioxide. One explanation is that Comet Read once included carbon dioxide but has now lost it due to heated temperatures.
Carbon dioxide vaporizes more quickly than water ice and may trickle out over billions of years, according to Kelley. "Being in the asteroid belt for a long time could do it," Kelley added. As an alternative, he suggested that Comet Read may have originated in a region of the solar system that was extremely warm and devoid of carbon dioxide.
According to scientist Heidi Hammel of the Association of Universities for Research in Astronomy (AURA), lead for Webb's Guaranteed Time Observations for solar system objects and co-author of the paper, the next step is expanding the research beyond Comet Read to examine how other main belt comets compare. These tiny, elusive objects in the asteroid belt may now be seen by Webb, allowing us to make inferences about them. Do other comets in the main belt lack carbon dioxide as well? In either case, finding out will be interesting, according to Hammel.
Milam, a co-author, considers how the study may be used locally. "It would be fascinating to follow up on this discovery with a sample collection mission, and learn what else the main belt comets can tell us now that Webb has confirmed there is water preserved as close as the asteroid belt."
