2023-05-08 18:00:00
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Astronomers used NASA’s James Webb Space Telescope to image the warm dust surrounding a nearby young star, called Fomalhaut, in order to study the first asteroid belt seen outside our solar system in infrared light. But to your surprise, these dust structures are much more complex than the Kuiper and asteroid dust belts in our solar system. Roughly speaking, there are three nested belts that extend to a distance of 23 billion kilometers (14 billion miles) from the star; that’s 150 times the distance from Earth to the Sun. The scale of the outermost belt is almost twice the scale of the Kuiper belt of our solar system, made up of small celestial bodies and cold dust beyond Neptune. The inner Fomalhaut belts—never seen before—were first revealed by Webb.
The belts surround this hot young star, which can be seen with the naked eye as the brightest star in the southern hemisphere constellation Pez Austral. Dust belts are the remnants of larger body collisions, analogous to asteroids and comets, and are often described as “rubble disks.” “I would describe Fomalhaut as the archetypal debris disk found elsewhere in our galaxy, because it has components similar to those found in our own planetary system,” said András Gáspár, of the University of Arizona in Tucson and lead author of a new scientific paper describing these results. “By looking at the patterns in these rings, we can start to make a little sketch of what a planetary system might look like, if we could indeed take an image deep enough to see the possible planets.”
The Hubble Space Telescope and Herschel Space Observatory, as well as the Atacama Large Millimeter/submillimeter Array (ALMA), have previously taken sharp images of the outermost belt. However, none of them found any structure inside. The inner belts have been resolved in infrared light for the first time by Webb. “What Webb is really outstanding at is that he allows us to physically resolve the thermal glow of dust in those inner regions. So we can see inner belts that we’ve never seen before,” said Schuyler Wolff, another member of the University of Arizona team.
This image of the dusty debris disk surrounding the young star Fomalhaut was obtained with Webb’s Mid-Infrared Instrument (MIRI). The image reveals three nested belts stretching out to a distance of 23 billion kilometers (14 billion miles) from the star. The inner belts—never seen before—were first revealed by Webb. The labels on the left indicate the individual characteristics. On the right, a large dust cloud stands out and the inset images show it at two infrared wavelengths: 23 and 25.5 microns.
Credit: NASA, ESA, CSA, A. Gáspár (University of Arizona). Image processing: A. Pagan (STScI)
Hubble, ALMA and Webb have teamed up to put together a holistic view of the debris disks around various stars. “With Hubble and ALMA, we were able to image a lot of Kuiper belt analogues, and we’ve learned a lot about how outer disks form and evolve,” Wolff said. “But we need Webb to allow us to image a dozen asteroid belts elsewhere. It is possible to learn as much about the warm inner regions of these disks as Hubble and ALMA have taught us about the cooler outer regions.”
Most likely these belts are forged by gravitational forces produced by unseen planets. Similarly, within our solar system, Jupiter corrals the asteroid belt, the inner edge of the Kuiper belt is sculpted by Neptune, and the outer edge could be guided by as-yet-unseen bodies beyond it. As Webb images more systems, we will learn about the configuration of planets from him.
The Fomalhaut dust ring was discovered in 1983 in observations made by NASA’s Infrared Astronomy Satellite (IRAS). The existence of the ring has also been inferred from earlier, longer-wavelength observations using the submillimeter telescopes on Mauna Kea, Hawaii, NASA’s Spitzer Space Telescope, and the Caltech Submillimeter Observatory.
“The belts around Fomalhaut are kind of a mystery novel: where are the planets?” said George Rieke, another member of the team and US chief scientist for MIRI’s Mid-Infrared Instrument (MIRI). Webb, who made these observations. “I think it wouldn’t be too hasty to say that there probably is a really interesting planetary system around the star.”
“We definitely didn’t expect to find the more complex structure with the second intermediate belt and then the broader asteroid belt,” Wolff said. “That structure is very exciting because every time astronomers see a gap and rings in a disk, they say, ‘There might be a planet in there shaping the rings!'”
Webb also took images of what Gáspár calls “the big dust cloud,” which could be evidence of a collision occurring in the outer ring between two protoplanetary bodies. This is a different feature of a possible planet, first seen by Hubble in 2008 within the outer ring. Subsequent Hubble observations showed that by 2014 the object had disappeared. Perhaps a plausible interpretation is that this newly discovered feature, like the one above, is an expanding cloud of very fine dust particles from two icy bodies that collided and disintegrated.
The idea that protoplanetary disks exist around stars dates back to the late 18th century, when astronomers Immanuel Kant and Pierre-Simon Laplace separately developed the theory that the Sun and planets formed from a cloud of gas. in rotation that collapsed and flattened due to gravity. The debris disks develop later, after the formation of the planets and the dispersion of primordial gas in the systems occur. This debris shows that small bodies such as asteroids collide catastrophically and pulverize their surfaces creating huge clouds of dust and other debris. Observations of its dust provide unique clues to the structure of exoplanetary systems, reaching detail down to Earth-sized planets and even asteroids, which are too small to see individually.
The team’s results have been published in the scientific journal Nature Astronomy.
The James Webb Space Telescope is the world’s premier space science observatory. Fomalhaut’s observations used the Mid-Infrared Instrument (MIRI), which was contributed by NASA and ESA (European Space Agency). This instrument was designed and built by a nationally funded consortium of European Institutes (the European MIRI Consortium) and NASA’s Jet Propulsion Laboratory (JPL), in partnership with the University of Arizona. 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 and the Canadian Space Agency (CSA).
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