The DART Mission involved sending a spacecraft to collide with an asteroid. Find out how it demonstrated the feasibility of NASA’s planetary defense strategy and exceeded expectations.
We had tuned into the NASA channel, and I was spellbound. It was September 26, 2022 and the Double Asteroid Redirection Test (DART) was closing in on the Didymos-Dimorphos asteroid system.
As readers will realize, especially if they watched the movie Don’t Look Up, our planet is at risk of a collision with a very large asteroid. Although astronomers don’t see any immediate threat, anything that can happen eventually does happen.
So, it’s only a matter of time before an asteroid like the one that wiped out the dinosaurs, or the one that leveled the forests around Tunguska, Siberia strikes again. DART was NASA’s first attempt at finding a way to avoid that kind of catastrophe.
ASteroid Impact Mission Was Successful
As we watched the screen, DART drew closer and closer to Dimorphos until the screen went blank without warning. Although losing the signal from a spacecraft is usually a bad thing, in this case, it was exactly what the researchers were hoping would happen. It meant the impact mission was successful.
As we reported back at the end of September, DART’s preliminary results exceeded expectations. Now, a presentation at the American Geophysical Union has announced that the mission had an even greater impact (pun intended) than the researchers realized.
Didymos-Dimorphos is a system in which the asteroid Didymos has a tiny moonlet orbiting it called Dimorphos. The idea of the DART mission was to crash into Dimorphos with a 570-kilogram spacecraft, knock it off course, and measure the results.
DART’s Goal: Shorten Orbit by Ten Minutes
Dimorphos orbits Didymos every 11 hours and 55 minutes. DART’s mission was to shorten that orbit by about ten minutes.
The preliminary results showed that the actual orbital change was 33 minutes, so DART beat its target by over 300%. Since then, scientists have been observing the system to collect further data.
The researchers are discovering that the impact raised much more debris, or ejecta, than expected. That’s good news because it means DART’s deflection technique, called “kinetic impactor technology” works even better than scientists thought it would.
For Every Action, Equal and Opposite Reaction
“The amount of momentum that you put in the target is exactly equal to the momentum that the spacecraft came in with,” DART investigation team lead Andy Cheng explained. As we all know, for every action, there’s an equal and opposite reaction.
However, in DART’s case, raising all that ejecta means that “you end up with a bigger deflection” according to Professor Chang. “If you’re trying to save the Earth, that makes a big difference.”
Ever since the impact, astronomers have been following Didymos and Dimorphos with space and ground-based telescopes. They can see a debris plume stretch out for tens of kilometres.
Ejecta Would Have a Mass of 1,000 Tonnes
That volume of ejecta would have a mass of at least 1,000 tonnes. It would fill about ten railway freight cars, according to Andy Rivkin, another DART investigation team lead.
Back in 2005, NASA crashed a space craft called Deep Impact into a comet called 9P/Tempel 1. Interestingly, the debris plume from Dimorphos is quite different from the one from the comet.
Apparently, Dimorphos and Tempel 1 are made of quite different stuff. Dimorphos appeared to be covered with boulders in the impact video, while the comet has a smoother surface and consists of granular dust.
Are the Two Asteroids Made of the Same Material?
The debris plume answered another question astronomers have been asking for many years. Are the two bodies in binary asteroids made of the same material?
Before the DART impact, most of the visible light from the system reflected off Didymos. After the collision, more than two-thirds of the light came from the debris from Dimorphos.
That gave astronomers the chance to capture the spectra of both objects. Since those spectra are remarkably similar, they likely have similar compositions.
Two Partners Made of Same Substances
So, at least in the case of Didymos-Dimorphos, the two partners in a binary asteroid are indeed made of the same substances. This finding sheds light on other research involving similar systems.
There’s an endless debate about the value of space exploration. Given the risks and the enormous costs, is it the best use of humanity’s resources?
In this case, there seems to be a solid rationale for DART’s $325 million price tag. When we consider that it shows us how to save our planet, it seems like a bargain.
And Another Thing…
As well, as with all space missions, DART has uncovered new insights into the universe and our place in it. Besides, everyone loves a hero’s journey, even when the hero is a robot.
The European Space Agency will be weighing in on the Dimorphos impact in 2026. Their Hera spacecraft will arrive at Dimorphos in late December of that year.
Hera will gather new information about the nature of both Didymos and Dimorphos. It will also get a closer look at the crater DART left on Dimorphos and measure how much momentum DART transferred to the tiny asteroid.
We always have more to learn if we dare to know.
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