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DART: What you need to know about NASA's mission to smash a spacecraft into an asteroid

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Illustration of NASA's DART probe, foreground right, and Italian Space Agency's (ASI) LICIACube, bottom right, at the Didymos system before impact with the asteroid Dimorphos.
Illustration of NASA's DART probe, foreground right, and Italian Space Agency's (ASI) LICIACube, bottom right, at the Didymos system before impact with the asteroid Dimorphos.   -   Copyright  Steve Gribben/Johns Hopkins APL/NASA via AP
By AP

NASA is about to clobber a small, harmless asteroid millions of kilometres away, in a first-of-its-kind, save-the-world experiment

A spacecraft named DART (Double Asteroid Redirection Test) will zero in on the asteroid on Monday, intent on slamming it head-on at 22,500 km/h. 

The impact should be just enough to nudge the asteroid into a slightly tighter orbit around its companion space rock – demonstrating that if a killer asteroid ever heads our way, we’d stand a fighting chance of diverting it.

“This is stuff of science-fiction books and really corny episodes of “StarTrek” from when I was a kid, and now it's real,” NASA program scientist Tom Statler said on Thursday.

Cameras and telescopes will watch the crash, which will be live-streamed on NASA TV from 6 pm ET (00:00 CET on Tuesday), but it will take days or even weeks to find out if it actually changed the orbit.

The $325 million (€333 million) planetary defense test began with DART's launch last year.

DART's target: Dimorphos

The asteroid with the bull’s eye on it is Dimorphos, about 9.6 million kilometres from Earth. It is actually the puny sidekick of a 780-metre asteroid named Didymos, Greek for twin. 

Discovered in 1996, Didymos is spinning so fast that scientists believe it flung off material that eventually formed a moonlet. Dimorphos – roughly 160 metres across – orbits its parent body at a distance of less than 1.2 kilometres.

“This really is about asteroid deflection, not disruption," said Nancy Chabot, a planetary scientist and mission team leader at Johns Hopkins University's Applied Physics Laboratory, which is managing the effort. 

"This isn’t going to blow up the asteroid. It isn’t going to put it into lots of pieces.” 

Rather, the impact will dig out a crater tens of metres in size and hurl about 1 million kg of rocks and dirt into space.

NASA insists there’s zero chance either asteroid will threaten Earth – now or in the future. That’s why the pair was picked.

The size of a golf cart

The Johns Hopkins lab took a minimalist approach in developing DART given that it’s essentially a battering ram and faces sure destruction. 

It has a single instrument: a camera used for navigating, targeting and chronicling the final action. 

Believed to be essentially a rubble pile, Dimorphos will emerge as a point of light an hour before impact, looming larger and larger in the camera images beamed back to Earth. 

Sometimes we describe it as running a golf cart into a Great Pyramid
Nancy Chabot
DART mission team leader

Managers are confident DART won’t smash into the larger Didymos by mistake. The spacecraft’s navigation is designed to distinguish between the two asteroids and, in the final 50 minutes, target the smaller one.

The size of a small vending machine at 570 kg, the spacecraft will slam into roughly 5 billion kg of asteroid.

“Sometimes we describe it as running a golf cart into a Great Pyramid,” said Chabot.

Unless DART misses its target – NASA puts the odds of that happening at less than 10 per cent – it will be the end of the road for the spacecraft. 

If it goes screaming past both space rocks, it will encounter them again in a couple of years for Take 2.

Saving Earth

Little Dimorphos completes a lap around big Didymos every 11 hours and 55 minutes. The impact by DART should shave about 10 minutes off that. 

Although the strike itself should be immediately apparent, it could take a few weeks or more to verify the moonlet’s tweaked orbit. Cameras on DART and a mini tagalong satellite will capture the collision up close. 

Telescopes on all seven continents, along with the Hubble and Webb space telescopes and NASA’s asteroid-hunting Lucy spacecraft, may see a bright flash as DART smacks Dimorphos and sends streams of rock and dirt cascading into space. 

This is why we test. We want to do it now rather than when there’s an actual need
Andrea Riley
NASA program executive

The observatories will track the pair of asteroids as they circle the sun, to see if DART altered Dimorphos’ orbit.

In 2024, a European spacecraft named Hera will retrace DART’s journey to measure the impact results.

Although the intended nudge should change the moonlet’s position only slightly, that will add up to a major shift over time, according to Chabot. 

"So if you were going to do this for planetary defense, you would do it five, 10, 15, 20 years in advance in order for this technique to work,” she said. 

Even if DART misses, the experiment still will provide valuable insight, said NASA program executive Andrea Riley. 

“This is why we test. We want to do it now rather than when there’s an actual need,” she said.

Asteroid missions galore

Planet Earth is on an asteroid-chasing roll. NASA has close to 450 g of rubble collected from asteroid Bennu headed to Earth. The stash should arrive next September. 

Japan was the first to retrieve asteroid samples, accomplishing the feat twice. China hopes to follow suit with a mission launching in 2025. 

NASA’s Lucy spacecraft, meanwhile, is headed to asteroids near Jupiter, after launching last year. 

Another spacecraft, Near-Earth Asteroid Scout, is loaded into NASA’s new moon rocket awaiting liftoff; it will use a solar sail to fly past a space rock that’s less than 18 metres next year. 

In the next few years, NASA also plans to launch a census-taking telescope to identify hard-to-find asteroids that could pose risks. 

One asteroid mission is grounded while an independent review board weighs its future. NASA’s Psyche spacecraft should have launched this year to a metal-rich asteroid between Mars and Jupiter, but the team couldn’t test the flight software in time.

From 'Armageddon' to 'Don't Look Up'

Hollywood has churned out dozens of killer-space-rock movies over the decades, including 1998′s “Armageddon” which brought Bruce Willis to Cape Canaveral for filming, and last year's “Don’t Look Up” with Leonardo DiCaprio leading an all-star cast. 

The good news is that the coast seems clear for the next century, with no known threats. 

What’s worrisome, though, are the unknown threats. Fewer than half of the 140-metre objects have been confirmed, with millions of smaller but still-dangerous objects zooming around. 

“These threats are real, and what makes this time special, is we can do something about it,” Zurbuchen said. 

Not by blowing up an asteroid as Willis’ character did — that would be a last, last-minute resort — or by begging government leaders to take action as DiCaprio’s character did in vain. If time allows, the best tactic could be to nudge the menacing asteroid out of our way, like DART.