Describing something as being the size of a stadium may make it sound big, but that's a grain of sand as far as the enormity of our Solar System is concerned.
The James Webb Space Telescope has enabled astronomers to find the smallest asteroids ever discovered in the main asteroid belt between Mars and Jupiter.
It's discovered 138 new asteroids in the belt, ranging from the size of a stadium right down to as small as a bus.
This size range has not ever been observable with ground-based telescopes, astronomers say, and is a testament to the power of the James Webb Space Telescope.
The discovery
The asteroid belt is a ring of space rocks around the Sun, located between the orbits of Mars and Jupiter.
It's likely made up of material that was left over following the formation of our Sun: the same material out of which the planets formed.
As a result, asteroids are primordial remnants of the early Solar System, and can tell scientists a lot about how the Solar System formed and evolved.
This latest discovery was made by a team led by scientists at the Massachusetts Institute of Technology (MIT).
They repurposed Webb’s observations of a distant star and found a population of small asteroids.
These are the smallest ever detected in the main asteroid belt
The fact they're so small is helping scientists build a more accurate picture of the range of asteroids in belt, and how they've changed over time as they collide with one another.
"We now understand more about how small objects in the asteroid belt are formed and how many there could be," says Tom Greene, astrophysicist at NASA’s Ames Research Center in California’s Silicon Valley and co-author of the study.
"Asteroids this size likely formed from collisions between larger ones in the main belt and are likely to drift towards the vicinity of Earth and the Sun."
Protecting Earth
The research could be of particular use to the Asteroid Threat Assessment Project at Ames.
ATAP supports NASA’s Planetary Defense Coordination Office by looking at what would happen if a large asteroid hit Earth.
"It’s exciting that Webb’s capabilities can be used to glean insights into asteroids," says Jessie Dotson, astrophysicist at Ames and member of ATAP.
"Understanding the sizes, numbers, and evolutionary history of smaller main belt asteroids provides important background about the near-Earth asteroids we study for planetary defence."
Caught on film
These newly-discovered tiny asteroids were found by analysing existing James Webb Space Telescope images
The team led by Artem Burdanov and Julien de Wit, both of MIT, developed a method to locate asteroids that may have been caught on film inadvertently by Webb.
Using a processing technique, they studied over 10,000 images of star TRAPPIST-1 that had originally been taken to look for atmospheres at planets orbiting the star.
Asteroids shine brightly in infrared, which is the wavelength Webb is designed to detect.
Thus, they were able to uncover a population of small asteroids that had gone unnoticed until now.
The study was presented in a paper entitled Detections of decameter main-belt asteroids with JWST on 9 December 2024 in Nature.
