May 15, 2023
The James Webb Space Telescope, a collaboration between NASA, ESA, and CSA, has made a groundbreaking discovery for Solar System scientists investigating the origins of water that has made life on Earth possible. The Webb telescope's Near-Infrared Spectrograph (NIRSpec) instrument has confirmed the presence of gas, specifically water vapor, around Comet 238P/Read, located in the main asteroid belt. This discovery proves that water from the primordial Solar System can be preserved as ice in that region, opening up a new area of investigation for scientists.
Comet Read is a main belt comet, which periodically displays a halo, or coma, and tail like a comet, but resides in the main asteroid belt. Main belt comets are a relatively new classification, and Comet Read was one of the original three comets used to establish the category. Before this, comets were believed to originate in the Kuiper Belt and Oort Cloud, beyond the orbit of Neptune, where their ices could be preserved farther from the Sun. Comets are differentiated from asteroids by the frozen material that vaporizes as they approach the Sun, giving them their distinctive coma and streaming tail.
Scientists have long speculated that water ice could be preserved in the warmer asteroid belt inside the orbit of Jupiter, but definitive proof was elusive until the Webb telescope's recent observations. The discovery of water vapor in Comet Read now confirms that water ice from the early Solar System can indeed be preserved in the asteroid belt.
This discovery has opened up a new area of investigation for scientists who have long been puzzled by how water, which is essential for life, came to Earth. Stefanie Milam, Webb Deputy Project Scientist for Planetary Science and a co-author on the study reporting the finding, said, “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.”
Understanding the history of water distribution in the Solar System can help scientists understand other planetary systems and whether they could host an Earth-like planet. This discovery could pave the way for more in-depth investigations into the formation and evolution of the Solar System and potentially even other planetary systems.
The absence of carbon dioxide was another surprise in the observations of Comet Read. Typically, carbon dioxide makes up about 10 percent of the volatile material in a comet that can be easily vaporized by the Sun's heat. However, Comet Read had no detectable carbon dioxide, and scientists have put forward two possible explanations for this. One possibility is that Comet Read did have carbon dioxide when it formed, but it has since been lost due to warm temperatures. The second possibility is that Comet Read may have formed in a particularly warm pocket of the Solar System where no carbon dioxide was available.
Michael Kelley, lead author of the study and an astronomer at the University of Maryland, said, "Being in the asteroid belt for a long time could do it – carbon dioxide vaporizes more easily than water ice and could percolate out over billions of years." Regardless of the reason, this discovery is significant for scientists, and further investigations into other main belt comets are necessary to understand the full picture.
Heidi Hammel, lead for Webb’s Guaranteed Time Observations for Solar System objects and co-author of the study, said, "These objects in the asteroid belt are small and faint, and with Webb, we can finally see what is going on with them and draw some conclusions. Do other main belt comets also lack carbon dioxide? Either way, it will be exciting to find out."
The study, published in the journal Nature, concludes that this discovery could lead to further investigations, such as sample collection missions, to learn more about main belt comets and what they can tell us about the Solar System