Tiny Treasures: The Discovery of the Smallest Main-Belt Asteroids in JWST’s Insights

Back to Article List

Researchers at MIT have detected 138 near-Earth objects utilizing a standard astrophotography method.

Over the last two centuries, astronomers have recorded more than a million asteroids within the solar system’s primary belt, down to approximately a kilometer in diameter. However, it was difficult to detect smaller asteroids — until now, when a group of scientists employed data gathered from the James Webb Space Telescope (JWST) to identify tiny asteroids as diminutive as 33 feet (10 meters) wide — comparable in size to a school bus.

Decameter asteroids — which denote those measuring tens of meters — originate in the main asteroid belt located between Mars and Jupiter. Due to the fact that smaller asteroids are more vulnerable to solar radiation and thermal variations modifying their paths, they are more prone to escaping the belt and colliding with Earth approximately every few years. Upon impact, they can result in considerable devastation. For example, in Chelyabinsk, Russia, 2013, a roughly 60-foot-wide (18 meters) asteroid detonated mid-air, generating a shockwave that harmed thousands and damaged numerous structures. Detecting these objects at their source within the main belt could significantly enhance our capability to track potential dangers.

To uncover these asteroids, the team, directed by MIT planetary scientists Artem Burdanov and Julien de Wit, employed archival JWST data alongside novel processing algorithms. In a paper released in Nature on December 9, they announced the identification of 138 asteroids smaller than 328 feet in diameter (100 meters) — marking the smallest ever discovered in the main asteroid belt.

A change in strategy

Since 2016, de Wit and his group have been utilizing the Transiting Planets and Planetesimals Small Telescope (TRAPPIST) in Chile to deepen their understanding of the star TRAPPIST-1 and its multitude of exoplanets. Within this research area, objects such as asteroids are considered nuisances that scientists eliminate, alongside the “noise” produced by gas and dust between us and the primary target.

“For the majority of astronomers, asteroids are often perceived as the pests of the skies, as they merely traverse your field of view and interfere with your data,” remarked de Wit in an MIT news announcement.

Nonetheless, de Wit and Burdanov identified an opportunity. Rather than disregarding asteroids, they aimed to locate them via an image-processing method referred to as synthetic tracking. This technique employs multiple short exposures of a stable field of view and merges them while shifting them in different directions. If a faint object is moving across the field of view at the same speed and direction as the shift, stacking the adjusted images can expose it — as if the camera had been directly tracking the object to begin with.

As the object could be positioned anywhere within the field and moving in any direction, testing the extensive range of potential shifts is exceptionally computationally demanding. To handle all the data, the team developed software that leverages commercially available graphics cards, or graphics-processing units (GPUs). (Preceding software for synthetic tracking was originally designed for traditional — and slower — central processing units, or CPUs.)

The group experimented with this approach using infrared data from various ground-based telescopes, including the Search for habitable Planets EClipsing ULtra-cOOl Stars (SPECULOOS) project and the Antarctic Search for Transiting ExoPlanets (ASTEP). They chose to test the technique on telescopes that operate in infrared rather than visible light since main-belt asteroids are dark, yet they absorb radiation from the Sun, making them significantly easier to detect in infrared frequencies. This method acted as proof of concept, leading to the publication of their findings in two papers in 2023.

Detailed analysis

For the recent Nature study, the team utilized 93.5 hours of observations of TRAPPIST-1 from JWST. Given that the telescope did not adjust its field of view during its observing sessions, the data was perfectly suited for the synthetic tracking approach.

The total discovery of 138 decameter asteroids significantly exceeded the team’s expectations. A handful of these asteroids could potentially become near-Earth objects at some future point, while one is anticipated to evolve into a Trojan — an asteroid that orbits the Sun ahead of or behind Jupiter in its path, outside the main belt.

According to the paper, the researchers aim to ultimately utilize JWST’s observations of 15 to 20 exoplanet-hosting stars to locate hundreds more decameter-sized asteroids from the main belt.

The team asserts that the sheer quantity of decameter asteroids they uncovered indicates that they are discovering a previously unseen population — those asteroids resulting from larger asteroids colliding and fragmenting. “This is a completely new, uncharted territory we are exploring, thanks to modern technologies,” Burdanov stated in the MIT release. “It exemplifies what can be achieved in our field when we analyze our data from a different perspective. Sometimes there’s a significant reward, and this is one such instance.”