Most observatories dedicated to searching for asteroids rely on the reflection of sunlight on their surfaces. However, a small asteroid, if it has a reflective surface, can shine just as brightly as a larger, less reflective asteroid. This method is therefore not the most reliable for determining the size of an asteroid.
Ideally, a telescope capable of seeing infrared light would be used to detect their thermal signals. “Many of these objects are much brighter in the infrared spectrum,” explains Julien de Wit, co-author of the study and a planetary scientist at MIT. In infrared, a larger asteroid will always shine brighter than a smaller one, regardless of its outer coating, making it a much more reliable tool for estimating its size.
Since the JWST has a very advanced infrared observation capability, De Wit and Burdanov had the idea of trying to use it to their advantage. It remained to be determined whether this was possible.
To do this, scientists turned to a method developed in the 1990s: “shift-and-stack”. Suppose a telescope captures several images of the same part of space, and an asteroid appears in them as a very faint moving light source. If we superimpose several shots of this weak source while following its movements over the images, it is possible to amplify the “luminosity” of the source, and thus determine what type of object it is. : in this case, from an asteroid.
The team tested whether this method worked using two Earth-based observatories dedicated to searching for exoplanets. The result was more than positive: hundreds of small objects (from asteroids in the main belt to space rocks that follow Jupiter) were spotted, including potentially forty-three that had not yet been detected.
The team then focused their efforts on TRAPPIST-1, a system located 40 light-years from Earth that is home to several rocky exoplanets. From the 10,000 images already taken by the JWST, the team identified 138 new asteroids in its main belt, ranging in size from about 600 meters long to just a few meters in diameter.
Main-belt asteroids in a stable orbit pose no danger. This study, however, shows that it is possible to use JWST, while it performs other tasks, to identify asteroids that, although small, are large enough to pose a potential threat. Then, if necessary, JWST can partner with other observatories to track these asteroids and determine whether any of them are headed toward our planet.
Most often, JWST is busy studying the distant cosmos. “Asteroids are not observed much,” says Sabina Raducan, a planetary scientist at the University of Bern, Switzerland, who was not involved in the new study. “However, it’s really interesting to see all the different types of science we can do just by looking at something else” in one image.
Indeed, using JWST to find asteroids only has advantages, because it does not detract from the effectiveness of its main missions; the discovery of Burdanov and his team is therefore welcome. NASA is nevertheless working on the design of another space telescope called Near-Earth Object Surveyor (or NEO Surveyor) equipped with infrared detectors and entirely dedicated to this mission. This should be launched in the coming years.
De Wit is keen to emphasize that the JWST will not dethrone the NEO Surveyor even before its launch, nor will it rule out ground-based observatories that are already very effective at spotting asteroids, such as the Vera-C.-Rubin Observatory in Chile, a new generation optical telescope which should make it possible to identify millions of new asteroids during its first year of operation.
“The JWST will in no way encroach on their mission,” says de Witt, but according to his team’s research, it will help to defend our planet. If JWST captures the same asteroid in multiple images, we can begin to determine its orbit and, with the help of other observatories, determine whether or not it is a main-belt asteroid on its way to becoming a near-Earth asteroid.
“If a potential impactor is discovered, JWST will be the best tool to obtain preliminary information on its size, composition, etc. These can be used to plan mitigation measures and help design possible reconnaissance missions,” says Rivkin. It is essential to know the properties of an asteroid that is heading toward Earth in order to determine whether it is best to attempt to deflect it or completely destroy it.
Ultimately, this study once again confirms that JWST is “a really great tool” that can be used for many more purposes than we thought, Burdanov admits; and when it comes to defending our planet against potential deadly threats, any tool is available.
