This artist’s concept of Comet 238P/Read shows the main belt comet sublimating—its water ice vaporizing as its orbit approaches the Sun. This is significant, as the sublimation is what distinguishes comets from asteroids, creating their distinctive tail and hazy halo, or coma. The James Webb Space Telescope’s detection of water vapor at Comet Read is a major benchmark in the study of main belt comets, and in the broader investigation of the origin of Earth’s abundant water.
“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 deputy project scientist for planetary science and a co-author on the study reporting the finding. “Understanding the history of water distribution in the solar system will help us to understand other planetary systems, and if they could 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 which periodically displays a halo, or coma, and tail like a comet. Main belt comets themselves are a fairly new classification, and Comet Read was one of the original three comets used to establish the category. Before that, comets were understood to reside in the Kuiper Belt and Oort Cloud, beyond the orbit of Neptune, where their ices could be preserved farther from the Sun. Frozen material that vaporizes as they approach the Sun is what gives comets their distinctive coma and streaming tail, differentiating them from asteroids. 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 Webb.
“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,” explained astronomer Michael Kelley of the University of Maryland, lead author of the study.
“With Webb’s observations of Comet Read, we can now demonstrate that water ice from the early solar system can be preserved in the asteroid belt,” Kelley said.
The missing carbon dioxide was a bigger surprise. 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. The science team presents two possible explanations for the lack of carbon dioxide. One possibility is that Comet Read had carbon dioxide when it formed but has lost that because of warm temperatures.
“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,” Kelley said. Alternatively, he said, Comet Read may have formed in a particularly warm pocket of the solar system, where no carbon dioxide was available.
This image of Comet 238P/Read was captured by the NIRCam (Near-Infrared Camera) instrument on NASA’s James Webb Space Telescope on September 8, 2022. It displays the hazy halo, called the coma, and tail that are characteristic of comets, as opposed to asteroids. The dusty coma and tail result from the vaporization of ices as the Sun warms the main body of the comet.
Credits: NASA, ESA, CSA, M. Kelley (University of Maryland). Image processing: H. Hsieh (Planetary Science Institute), A. Pagan (STScI)
The next step is taking the research beyond Comet Read to see how other main belt comets compare, says astronomer 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 study. “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,” Hammel said.
Co-author Milam imagines the possibilities of bringing the research even closer to home. “Now that Webb has confirmed there is water preserved as close as the asteroid belt, 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.”
The study is published in the journal Nature.
THE JAMES WEBB SPACE TELESCOPE MAY HAVE SPOTTED A BABY GALAXY MERGER
New JWST images reveal that one of the most distant objects ever observed is actually two baby galaxies on a possible collision course.
The massive gravity of galaxy cluster MACS0647 acts as a cosmic lens to bend and magnify light from the more distant MACS0647-JD system. It also triply lensed the JD system, causing its image to appear in three separate locations. These images, which are highlighted with white boxes, are marked JD1, JD2, and JD3; zoomed-in views are shown in the panels at right.
Science: NASA / ESA / CSA / Dan Coe (STScI) / Rebecca Larson (UT) / Yu-Yang Hsiao (JHU); Image processing: Alyssa Pagan (STScI)
Big galaxies like the Milky Way — a spiral disk 100,000 light years across containing some 200 billion stars — are thought to come from the celestial meet-and-greets of the first galaxies, which were originally little more than tiny clumps of stars. Now, the James Webb Space Telescope (JWST) has imaged two baby galaxies that existed just 430 million years after the Big Bang, each only hundreds of light-years across. Astronomers think they might be merging, shedding light on galaxy growth in the early universe.
“Most galaxies today will have been through several merger events,” says Tiger Yu-Yang Hsiao, (Johns Hopkins University), who led the study. “So [mergers] are key to studying the formation and evolution of galaxies today. Our target is from such an early time, right at the very beginning of this process. There is much we can learn from it.”
MACS0647–JD (MACS-JD) is an extremely distant object first observed about 10 years ago. At the time, it was considered to be the most distant galaxy ever observed, and it is still one of the earliest things we can study in detail with JWST.
Generally speaking, galaxies from the dawn of time are too faint and too far away to see. The reason we can see MACS-JD is because its light has been triply lensed, magnified and distorted by a massive galaxy cluster lying in front of it from our point of view. The cluster warps spacetime, splitting the light into three images of the same system. The images are magnified by factors of eight, five, and two, so they appear brighter than other galaxies at similar distances.
Hsiao’s JWST observations of MAC-JD verified previous conclusions about its distance, size, and physical properties — but with a surprising twist. What was once seen as a single object now appears to be two baby galaxies, labeled A and B. A is brighter and larger with very recent star formation and no dust, while B looks older and has a little bit of dust. Their differing star formation histories suggest they formed farther apart, only coming together recently.
“The researchers did a very good job approaching this problem, but there is a lot of uncertainty,” says Andrea Ferrara (Scuola Normale Superiore, Italy), who was not part of the study. He suggests that while a merger is a possibility, it’s also possible that one of the galaxies is a satellite of the other. Alternatively, the two components might be part of the same galaxy.
“We do expect that galaxies at this very high redshift are in the assembly process,” he notes, but he adds that additional data about the galaxies’ motions would help clarify their relationship.
Hsiao’s team based this study, posted on the arXiv and accepted to Astrophysical Journal Letters, solely on JWST images. Upcoming spectroscopic observations, also with JWST, should tell us how A and B are moving with respect to each other. If they are both part of the same galaxy, the difference between their velocities would be relatively small; if they are actually two merging galaxies, there would be a larger discrepancy. Besides shedding light on the objects’ motions, spectra will also tell us more about the chemical properties of these tiny, highly magnified galaxies observed in the early universe.
JWST Will Hunt for Dead Solar Systems—And Much More—In Its Second Year of Science
White dwarfs, Earth-sized exoplanets, early galaxies and even Saturn’s moon Enceladus are on the agenda for JWST’s second year in space, but exomoons and others miss out
Where do you point the world’s most powerful space telescope? It’s not an easy question. The James Webb Space Telescope (JWST), launched in December 2021, has amazed astronomers since it began sending back its first science data in July 2022. It has seen galaxies breathtakingly close to the dawn of time, probed the atmospheres of exoplanets in unprecedented detail and provided stunning new views of worlds in our solar system. But it’s just getting started. Last week on May 10 astronomers learned if their proposals for the telescope’s second year of science were successful. Competition was fierce, and while there were plenty of winners and some incredible science set to be conducted, there were many more who missed out on JWST’s “Cycle 2,” which starts next month. “There was an extraordinary response from the science community,” says Nancy Levenson, interim director of the Space Telescope Science Institute (STScI) in Maryland, which runs JWST.
In total, astronomers submitted about 1,600 proposals to STScI for observing time on the NASA-led JWST. But only 249 were selected—meaning that JWST has an “oversubscription” of nearly 7 to 1, similar to that for the Hubble Space Telescope. To minimize the chance of bias, the process of selecting JWST’s programs is completely anonymous, with hundreds of astronomers from multiple subfields involved in the decision process. That said, there were clear winners and losers. Some astronomers, such as Nathan Adams of the University of Manchester in England, put forward multiple proposals that were rejected. “We had four proposals, and none of them got time,” Adams says. “Obviously we’re a bit disappointed.” Others, such as Mary Anne Limbach of Texas A&M University, were much more successful. Limbach had three proposals approved. “We’re excited about the time we got,” she says.
Limbach’s proposals are focused on white dwarfs, the remnant Earth-sized cores left behind after stars such as our sun swell into red giants and expel their outer layers. After this dramatic event, it’s thought these stellar corpses can still harbor intact planets—potentially offering us the chance to study them and learn more about the fate likely to befall Earth in five billion years when our sun enters its red giant phase. Limbach will attempt to confirm two suspected white dwarf worlds but will also search for up to a half dozen more elsewhere in the sky. “JWST can see if any of these nearby white dwarfs look brighter than they should be,” she says. “If they do, that could be an indicator there’s a planet there. JWST is really the only observatory capable of confirming them.”
A dominant area of JWST’s Cycle 1, which had about 1,200 proposals, was hunting for the earliest known galaxies in the universe, which were formed just a few hundred million years after the big bang. The same is true for Cycle 2, with both galaxies and exoplanets getting the most telescope time. An accepted proposal from Daniel Eisenstein of Harvard University is hoping to push JWST to its limits by hunting for galaxies perhaps up to just 200 million years post-big bang. Distances to faraway galaxies are measured in redshift—the degree to which light we see from a galaxy has been shifted to the red end of the spectrum by the universe’s expansion. Eisenstein will hunt for galaxies beyond redshift 15, farther than any others conclusively seen. “We don’t yet have a convincing case of a galaxy beyond redshift 15,” he says. “It’s really exciting to be able to continue the search that started in this first year.”
Rohan Naidu of the Massachusetts Institute of Technology will also be scouring the distant universe, but not for those highest-redshift galaxies. Instead, his program, which he co-leads with Jorryt Matthee of the Swiss Federal Institute of Technology in Zurich (ETH Zurich), will be using a giant cluster of galaxies called Abell 2744 to gravitationally magnify the light of some smaller objects up to 750 million years after the big bang. The goal is to look for clumps of primordial gas, which could contain clusters of Population III stars—the first stellar generation thought to have lit up the universe. These long-theorized objects have yet to be directly seen but are expected to be composed almost entirely of pure hydrogen and helium—which should allow them to be enormous, each weighing in hundreds of times heavier than our sun. “We’re really pushing JWST to the hilt,” Naidu says. “We’ll get back some very promising regions that might be hosting these clusters.”
A key target of interest for JWST’s Cycle 1 was the TRAPPIST-1 system, an arrangement of seven Earth-sized worlds—some of which might be habitable—around a red dwarf star about 40 light-years from Earth. While three TRAPPIST-1 programs were selected in Cycle 1, however, only one has been selected this time, led by Michaël Gillon of the University of Liège in Belgium. He will hunt for atmospheres on TRAPPIST-1b and c, the two innermost planets of the system. Early studies of TRAPPIST-1b suggest it has no atmosphere, but Gillon says his technique—measuring the temperature difference between the day and night side of the planet—will tell us for sure. That could have important implications for TRAPPIST-1’s other more temperate worlds that might conceivably support life. “If we can demonstrate that one of these two planets has an atmosphere, we will be in a very good position to ask for an ambitious program on JWST to dig into the other planets,” he says.
Closer to home, Christopher Glein of the Southwest Research Institute (SWRI) in Texas will use JWST to probe Saturn’s moon Enceladus, which may harbor a habitable ocean beneath its icy surface. Observations from NASA’s Cassini spacecraft, which orbited Saturn from 2004 to 2017, showed that the moon occasionally ejects water from this ocean via a plume at its south pole. While no spacecraft currently orbits Saturn, JWST is the next best thing. Incredibly, it will be able to “look for evidence of ocean chemistry” on the surface of Enceladus, Glein says. It will even be sensitive to certain substances, such as ammonia and various organic molecules, that could tell scientists about the habitability of the moon’s hidden ocean. In 2040 Enceladus’s south pole will enter a long winter of darkness that will last until 2055, making a potential future landing there to hunt for life difficult. Glein, however, is hoping to show with JWST that the moon’s polar plume is depositing frozen sea spray all across the surface, perhaps all the way up to the sunlit equator, where a landing could be more feasible. “JWST can act as a bridge between the Cassini era and a lander on Enceladus,” he says.
Not all areas of research were so lucky. David Kipping of Columbia University submitted two proposals to use JWST to hunt for moons orbiting exoplanets, known as exomoons. JWST “is the first machine humanity has ever built that is actually capable of doing this experiment,” Kipping says. But both proposals were rejected. “We’re definitely disappointed,” he says. “We really felt like this was a slam-dunk argument.”
JWST should be able to find exomoons down to the size of Europa, Kipping says, but even if it can’t, the results “would be pretty profound.” A failure to turn up an expected population of exomoons “would mean the models we use in our solar system aren’t universal,” he says, and could be a clue that our local abundance of lunar satellites is a bizarre deviation from cosmic norms. Time is of the essence, considering JWST is the only telescope now or for the foreseeable future that can look for exomoons. “JWST could last ten years, maybe longer,” Kipping notes. “If we never look for exomoons with it, we would really regret it. That would be such a shame.”
Levenson knows there will be some disappointment from the programs that were not selected. “There are lots of great ideas that we are not going to be able to observe during this cycle,” she says. For those that missed out, the deadline to try again and apply for Cycle 3 is October. “We have to keep trying,” Kipping says. “JWST is not going to be there forever.” For those lucky few that did make the cut, there are scientific riches to be had. “There’s this whole range of science that JWST is just great for,” says Levenson. “We’re definitely not done yet.”
Quelle: SCIENTIFIC AMERICAN
James Webb telescope discovers gargantuan geyser on Saturn's moon, blasting water hundreds of miles into space