NASA plans an ambitious mission next week that Canadians say will provide a small boost to asteroid science.
The mission is called DART (Double Asteroid Redirection Mission), and aims to send a spacecraft into the moonlet of an asteroid on Sept. 26. The target is called Dimorphos, which orbits around Didymos. If the mission goes to plan, the spacecraft will slightly alter the orbit of the moonlet, which will be observed from Earth with telescopes and later in the decade, up close via a European-led spacecraft called Hera.
The main goal of the mission is to demonstrate a form of planetary defence, called a kinetic impactor. That said, there are side benefits to the mission that will provide more insight into how asteroids were formed and are evolving, said Paul Wiegert, an astronomer at Western University who studies smaller bodies such as asteroids.
“One of the big questions that this mission will help to answer is what is underneath the surface of an asteroid,” Wiegert said, pointing out that past missions have tended to focus very much on the top layers.
“We might naively think that an asteroid is just a solid rock, but there’s some evidence that it’s actually lots of little rocks held together very weakly, but by their own gravity. This is important, because if you hit a solid rock, it’s very different from when you hit a sandbag, for example,” Wiegert added.
Two years ago, Wiegert wrote a Planetary Science Journal article speculating on the possibility of DART ejecta reaching Earth in the form of a meteor shower. (The asteroid is some 11 million km away, which is relatively close in celestial terms.)
“It turns out that really very little, if any, material will make that journey just because of the geometry and the other parameters of the impact,” he said, but astronomers will be watching for “some very low level activity,” just in case.
Western’s physics and astronomy department runs an all-sky camera network stretching across southern Ontario to monitor bolides and to examine the physics of meteor showers, among other investigations. Meteor showers, Wiegert said, tend to come from the same direction and at similar speeds, which makes it easier to distinguish any stray dust from DART on the off chance the mission does generate some dust.
Wiegert’s graduate student, David Clark, recently submitted a paper for peer-review to the Planetary Science Journal, concerning a bolide detected over the western Pacific, picked up by U.S. government sensors almost exactly two years ago on Sept. 18, 2020. Clark told SpaceQ it’s the first post-impact detection of an Earth-impacting object, only using archival images; the impact generated a 0.4 kiloton fireball over the Pacific.
“I have been responsible for a project nick-named FROSTI, Fireball Retrieval on Survey Telescopic Images, which identifies serendipitous images of Earth impactors,” he said. “We compute the in-space trajectory of any pre-fireball meteoroid which has been observed with sufficient accuracy, and which we believe to be large enough to be viewed in space.”
The project can detect meteoroids as small as 20 centimetres, and the project has catalogued millions of sky survey images. The new object was found during a periodic search of the catalogue conducted to look for interesting events.
Clark said that astronomers are trying to work towards a regime where they can detect incoming meteors in space, in the atmosphere and (assuming it drops meteorites) on the ground to better characterize their nature. Naturally, observations of asteroids like Didymos and Dimorphos — from which some meteors originate — supplement this work.
“The hope is that through ever-improving fireball detection systems and deeper sky surveys, we will make more of these discoveries,” Clark said of his research. “The main interest is in understanding the nature of near-Earth asteroids, for understanding their population, for risk assessment, and understanding their composition for risk mitigation.”
For example, the September 2020 event he described found that the object was “larger, less dense, and significantly darker than originally expected.” This analysis came from combining various observations.
The Atlas Sky Survey imaged the object and allowed investigators to define the orbit, the shape and the brightness (an indicator of the composition). U.S. government sensors, infrasound observations and lightning detection satellites gave a sense of the object’s incoming energy, which allowed a mass computation.
The Canadian Space Agency has no direct involvement in DART, but another mission coming back to Earth next year does have its participation. OSIRIS-REx (Origins, Spectral Interpretation, Resource Identification, Security-Regolith Explorer) is ferrying back a sample of asteroid Bennu for closer investigation, representing the first NASA-led effort to send space rock bits back to Earth.
Canadian investigators will get a guaranteed share of that sample thanks to contributing the OSIRIS-REx Laser Altimeter (OLA), a laser system which scanned Bennu from up to seven kilometres away and which also helped the spacecraft team determine a touch-and-go location for sample collection.
SpaceQ will broadcast a live NASA special of the impact on Monday, Sept. 26 starting at 6:00 pm EDT on our special events live streaming web page.