On Monday, NASA will attempt to smash its car-sized DART spacecraft into a non-threatening asteroid, in what is an important first test of a planetary defence strategy against hazardous celestial objects. A host of telescopes will be watching, including the Hubble and Webb space telescopes.
“We are moving an asteroid,” Tom Statler, DART program scientist, told reporters yesterday at a NASA press briefing. “We’ve never done that before,” he added, saying “it’s kind of astonishing that we’re doing that.” The capacity to deflect an asteroid would open up an “amazing frontier,” but it all starts with Monday’s test at Didymos, the “perfect natural laboratory for this double test,” said Statler. The spacecraft is expected to slam into Dimorphos, the smaller member of the Didymos binary asteroid system, at 9:14 a.m. ET on September 27.
By double test, Statler is referring to two distinct demonstrations that make up the $US308 ($428) million mission. The first is to build a spacecraft capable of slamming directly into an asteroid. DART, weighing 624 kg and guided by a cutting-edge autonomous navigation system, will hopefully be up for the task. The second test is to study how the asteroid responds to the impact. The question NASA scientists will be asking after the impact is, “how effectively did we move the asteroid and could we ever use this technology to move an asteroid should we need to?” Statler explained.
Should all go well, DART will change Dimorphos’s speed by around 1%, which should be enough to change the moonlet’s orbit. Mission scientists will be scrambling to confirm the full impact of the impact, using a host of tools to gather the required data. “We do not know how these tiny asteroids will behave,” said Statler, saying we have to go to space to do these sorts of experiments in order to improve our models and simulations of impacts.
Among these tools will be the Hubble Space Telescope and the recently deployed Webb Space Telescope. These instruments won’t observe the moment of impact — that would actually serve very little purpose — but will instead scan the system some 15 minutes after DART’s demise. Hubble will observe the Didymos system from Earth orbit, while Webb will perform its observations from the second Sun-Earth Lagrange point (L2). Didymos is currently 11 million km from Earth and roughly 9.7 million km from L2, so neither of the two space telescopes will have a close-up view.
Despite these distances, Hubble and Webb will search for signs of object brightening — an indication of the amount of dust kicked up by the impact. By measuring the degree of brightening and the length of time the impact plume persists, scientists can make inferences about the consistency of Dimorphos’s surface material. This data will teach us more about asteroids, but it could also improve our simulations of kinetic impactors, as scientists work to develop an effective planetary defence strategy against threatening asteroids.
To be crystal clear, DART, short for NASA’s Double Asteroid Redirection Test, will attempt to alter the orbital trajectory of a non-threatening asteroid. There is no risk to Earth, nor will the test put our planet into any danger. As Statler said, the Didymos system is serving as a kind of “lab” for this very important demonstration.
Didymos, meaning “twin” in Greek, is 780 metres wide, while Dimorphos, meaning “two forms,” is 160 metres wide, which is just shy of two football fields long. Dimorphos, nicknamed Didymoon, makes a complete orbit of Didymos every 11.9 hours. DART, launched 11 months ago, is expected to alter the orbital period of the moonlet by several minutes.
Webb and Hubble won’t be the only spacecraft with eyes on Didymos. NASA’s Lucy probe, currently en route to Jupiter’s Trojan asteroids, will use its onboard LORRI instrument to gather data in the minutes following the impact. Like Hubble and Webb, Lucy should detect some object brightening.
At the scene itself, DART’s DRACO instrument will snap one image per second as it zooms to its doom, reaching speeds of 22,531 km per hour. Needless to say, DART won’t be around to document the aftermath, which is why the probe brought a helper along for the ride: the Italian-built LICIACube (pronounced LEE-cha-cube). DART dispatched the probe a couple of weeks ago, and it is now travelling alongside its condemned companion. LICIACube will zip past Dimorphos roughly three minutes after the encounter to confirm the impact. The tiny probe, with its two cameras called LUKE and LEIA, will document the spread of the expanding plume, attempt to capture an image of the new crater, and document the non-impacting side of the moonlet.
“We are working with [the Italian Space Agency] to get LICIACube to within 40 to 80 kilometres of Dimorphos just two to three minutes after DART’s impact — close enough to get good images of the impact and ejecta plume, but not so close LICIACube could be hit by ejecta,” Dan Lubey, LICIACube navigation lead at NASA’s Jet Propulsion Laboratory, explained in a press release.
On Earth, NASA’s Deep Space Network will track the collision and its aftermath, while the European Space Agency will do the same with its Estrack Network, which includes dish antennas in Argentina and Australia.
After the impact, teams of scientists will race to find evidence of a potential orbital change, as each wants to be the first to confirm a successful redirection of Dimorphos, Statler said. He added that it could take a few days or several weeks to make the confirmation, because it’s difficult to know how the asteroid will react.
Earth is not currently threatened by a dangerous asteroid, but a dangerous object could always appear from out of the blue. NASA and its international partners want to be prepared for this grim possibility and develop the means to shove hazardous asteroids from harm’s way. DART is likely to be the first of many future experiments to acquire this civilisation-saving capability.
More: 9 Things to Know About NASA’s Armageddon Mission to Deflect an Asteroid.