JWST Finds the Smallest Asteroids Ever Seen in the Main Belt

The JWST was never intended to find asteroids. It was built to probe some of our deepest, most demanding questions about the cosmos: how the first stars formed, how galaxies have evolved, how planets like ours take shape, and even how life originated. However, it’s first and foremost a powerful infrared telescope and its unrivalled infrared prowess is helping it contribute to another important goal: defending Earth from dangerous asteroids.

Humanity doesn’t want to share the dinosaurs’ fate. About 66 million years ago, the Chicxulub impact wiped them out. An asteroid 10 to 15 km (6 to 9 mi) wide struck Earth near the Yucatan Peninsula, ending the dinosaurs’ 165-million-year reign. Only avian dinosaurs survived.

With that haunting backdrop, there’s a growing effort to identify dangerous space rocks that could strike Earth. In 2005, the US Congress directed NASA to “establish a Near-Earth Object Survey Program to detect, track, catalogue, and characterize certain near-Earth asteroids and comets.” That effort has paid dividends, especially when it comes to large asteroids that pose an existential threat.

Finding the largest main-belt asteroids hasn’t been difficult. They practically announce their presence to our powerful telescopes. Large asteroids around 100 kilometres in diameter or greater are potentially devastating, but they tend to follow stable orbits in the main belt.

However, decameter-size impactors are more elusive. These are asteroids tens of meters in diameter, and their smaller masses mean they can more easily become part of the Near-Earth Object (NEO) population due to interactions in the main belt. While these aren’t civilization-ending size rocks, they can reach Earth more frequently and cause megaton-size explosions. They’re behind the Tunguska Event in 1908 and the Chelyabinsk explosion in 2013.

The JWST is helping scientists understand this population of space rocks, and new research illustrates how. It’s titled “JWST sighting of decametre main-belt asteroids and view on meteorite sources.” It’s published in Nature, and the co-lead authors are Julien de Wit and Artem Burdanov, both from the Department of Earth, Atmospheric, and Planetary Sciences at MIT.

“Asteroid discoveries are essential for planetary-defence efforts aiming to prevent impacts with Earth, including the more frequent megaton explosions from decametre impactors,” the authors write. “Although large asteroids (~100 kilometres) have remained in the main belt since their formation, small asteroids are commonly transported to the near-Earth object (NEO) population.” NEOs are objects whose closest approach to the Sun is less than 1.3 AU. This boundary includes objects that can come close enough to cross Earth’s orbit or can be potentially influenced by Earth’s gravity.

Most asteroids are detected with ground-based optical telescopes that sense the sunlight they reflect, which is their albedo. Relying on asteroids’ albedo measurements, though, is fraught with errors. For example, small objects with a high albedo can appear larger than large objects with a small albedo.

Asteroids also give off thermal emissions or infrared energy, and that’s where the JWST comes in. “With an exquisite sensitivity in that wavelength range and a large aperture, JWST is ideal for detecting the thermal emission of asteroids and revealing the smallest main-belt asteroids (MBAs),” the authors write in their paper.

According to the researchers, the JWST’s infrared measurements can constrain an object’s size to within 10% to 20%, while albedo measurements alone can be off by a factor of 3-4x. That’s a huge discrepancy that could lead to a risky misunderstanding of the main asteroid belt’s population.

Burdanov, de Wit, and their co-researchers developed a new way to detect decametre-size impactors with the JWST by using GPUs, Graphics Processing Units, and what the researchers call “synthetic tracking techniques.” These were initially developed to hunt for exoplanets, but the method is bearing fruit in the effort to catalogue asteroids. The researchers’ synthetic tracking method is designed to detect asteroids in data gathered from exoplanet observations. The JWST observed the TRAPPIST-1 star for more than 90 hours in 2022-23, and these results are based on that data.

“After applying our GPU-based framework for detecting asteroids in targeted exoplanet surveys, we were able to detect 8 known and 139 unknown asteroids,” the authors write. “The 139 new detections could not be attributed to any known asteroids.”

They range from the size of a bus to several stadiums wide. They’re the smallest objects ever detected in the main asteroid belt.

“We have been able to detect near-Earth objects down to 10 meters in size when they are really close to Earth,” said author Artem Burdanov in a press release. “We now have a way of spotting these small asteroids when they are much farther away, so we can do more precise orbital tracking, which is key for planetary defence.”

“For most astronomers, asteroids are sort of seen as the vermin of the sky, in the sense that they just cross your field of view and affect your data,” study co-author Julien de Wit said.

via GIPHY

de Wit explained the background of this research to Universe Today. Their interest in using the JWST in this way preceded the telescope’s launch.

De Wit and his co-researchers helped discover the TRAPPIST-1 system in 2016. In exoplanet science, objects like asteroids are considered noise that interferes with attempts to detect exoplanets. These asteroids are basically tossed aside in those efforts. In more recent years, astronomers pointed the JWST at the TRAPPIST-1 system and used its infrared capabilities to measure the temperature of the innermost planet and observe stellar flares. Those observations created what de Wit calls “bonus science.”

“Our main line of work relates to detecting and studying exoplanets like the TRAPPIST-1’s seven terrestrial gems,” de Wit explained. “But over the years, we’ve also been wanting to do more with all the astronomical data gathered by exoplanet surveys, and we started mining these fields of view for “bonus science.” One of them relates to detecting objects crossing the field of view, like asteroids. We perfected our methodology ahead of JWST, knowing that synthetic tracking combined with JWST’s unparalleled capabilities in the infrared (part of the wavelength range where these asteroids are the brightest) would change the game.”

These results are just a beginning. Every time the JWST is trained on something, it creates data. All of that data can be combed through to detect more asteroids and to try to understand what family they belong to. Decameter-size asteroids are likely the result of collisional cascades, and researchers would like to understand some of those relationships.

“There is a LOT more archival data to be used as done here. We are now gearing up to mine all of it,” de Wit explained, though it depends on funding. “This would allow us to study the 3D structure of the main belt and relate different sub-populations of these decameter asteroids to specific families of asteroids (and meteorites)!”

We’re expecting thousands of these asteroids in the existing MIR data!” said de Wit.

The discovery of the potentially dangerous asteroid 2024YR4 has focused peoples’ attention on the asteroid threat. It’s a NEO with a small chance of impacting Earth in 2032, though scientists caution against any panic. It’ll pass close to Earth again in 2028 and will be subjected to more precise observations and a reassessment of its risk.

Observing time with the JWST is a hot commodity. We asked the researchers if they’ll have an opportunity to use the space telescope to purposefully detect more asteroids.

“We did put forth a “catch me if you can” proposal with the intent of demonstrating JWST’s capabilities to detect decameter MBAs and then follow up on them to constrain their orbits as a “performance test” for planetary defence efforts,” de Wit said. He explained that “possible impactors often have their aphelion up in the main belt and constraining their orbit well can use observations all the way out there.” Their proposal is waiting for approval.

The 139 new asteroids detected in the main belt are bonus science. The team’s observation method had limitations and wasn’t dedicated to finding the smallest asteroid. However, there’s a lot more JWST data waiting to be mined, and with a more dedicated effort, de Wit and his co-researchers could detect many more.

“An observational setup that would allow for JWST to “drift” along the expected motion of smaller asteroids in the main belt while performing longer exposures would allow for asteroids below 10 meters to be detected,” de Wit told Universe Today.

“With an observational set up dedicated to detecting the smallest main-belt asteroids, we could go much smaller,” de Wit concluded.

The post JWST Finds the Smallest Asteroids Ever Seen in the Main Belt appeared first on Universe Today.

Source: https://www.universetoday.com/170834/jwst-finds-the-smallest-asteroids-ever-seen-in-the-main-belt/