NASA’s asteroid-deflecting DART mission explained

By William On Sep 12, 2022

Smashing a spacecraft into an asteroid in a bid to throw it off course may evoke memories of a Hollywood disaster movie such as Armageddon or Deep Impact.

But this is definitely not fiction — in fact, it’s NASA’s ambitious planetary defence test that if successful could one day pave the way for protecting Earth from a catastrophic impact from space.

It is the US space agency’s first ever attempt at such a mission and will involve a spacecraft crashing into an asteroid 6.8 million miles from Earth at 15,000mph in two weeks’ time.

The Double Asteroid Redirection Test (DART) was launched last November ahead of an almost year-long journey to crash into the small asteroid Dimorphos, which orbits a larger one called Didymos.

Didymos and Dimorphos will make their closest approach to Earth in years in late September, passing at a distance of about 6.7 million miles (10.8 million kilometres) from the planet.

The impact is due to take place on Monday, September 26 at 19:14 ET (00:14 BST) and can be watched live on NASA TV and the agency’s YouTube channel.

Rome-based Virtual Telescope Project has also teamed up with several observatories in South Africa and will be showing the target asteroid in real-time at the moment of the scheduled impact.

The animation and graphic below shows how the mission will work, while MailOnline also explains the test’s purpose and how it compares to a couple of the more famous asteroid-related disaster movies.

Brace for impact: NASA’s first ever ‘planetary defence’ spacecraft – sent to deflect an asteroid 6.8 million miles from Earth – is set to hit its target on Monday, September 26. The graphic above shows how the mission will work

The spacecraft has captured images of its target double-asteroid system, which includes the asteroid it will crash into, called Dimorphos, the asteroid moonlet of Didymos

The Double Asteroid Redirection Test was launched last November ahead of a year-long journey to crash into the small asteroid Dimorphos, which orbits a larger one called Didymos

WHAT IS THE NASA DART MISSION?

DART will be the world’s first planetary defence test mission.

It is heading for the small moonlet asteroid Dimorphos, which orbits a larger companion asteroid called Didymos.

When it gets there it will be intentionally crashing into the asteroid to slightly change its orbit.

While neither asteroid poses a threat to Earth, DART’s kinetic impact will prove that a spacecraft can autonomously navigate to a target asteroid and kinetically impact it.

Then, using Earth-based telescopes to measure the effects of the impact on the asteroid system, the mission will enhance modelling and predictive capabilities to help us better prepare for an actual asteroid threat should one ever be discovered.

Astronomers say that anybody tuning it to watch the impact may well be able to spot changes in brightness of the asteroid as a result of the collision.

That’s if it is successful, of course, which wasn’t quite the case in Deep Impact.

The 1998 film depicts the attempts to prepare for and destroy a 7-mile (11 km) wide asteroid that is set to collide with Earth and cause a mass extinction.

A team of astronauts are sent to land on the space rock and drill nuclear bombs deep beneath its surface, but rather than deflect the asteroid, when they’re detonated they only split it in two.

The smaller fragment goes on to hit Earth, creating a megatsunami that destroys much of the East Coast of the United States and also hits Europe and Africa, before the spacecraft and its crew that deployed the nuclear bombs sacrifice themselves by crashing into the bigger remnant of the asteroid and blowing it into smaller pieces.

It is the latter technique that bears a similarity to the real-life DART mission, although there won’t be any nuclear bombs involved.

Part of the reason is that when the $325 million (£240 million) DART craft hits Dimorphos, the plan is for it to change the speed of the ‘moonlet’ by a fraction of a per cent, rather than obliterate it.

Although the 525ft-wide space rock doesn’t pose a danger to Earth, NASA wants to measure the asteroid’s altered orbit caused by the collision.

This demonstration of ‘planetary defence’ will inform future missions that could one day save Earth from a deadly asteroid impact.

‘This isn’t going to destroy the asteroid. It’s just going to give it a small nudge,’ said mission official Nancy Chabot of Johns Hopkins Applied Physics Laboratory, which is managing the project.

Dimorphos completes an orbit around Didymos every 11 hours and 55 minutes ‘just like clockwork’, she added.

DART’s goal is a crash that will slow Dimorphos down and cause it to fall closer toward the bigger asteroid, shaving 10 minutes off its orbit.

The change in the orbital period will be measured by telescopes on Earth. The minimum change for the mission to be considered a success is 73 seconds.

The DART technique could prove useful for altering the course of an asteroid years or decades before it bears down on Earth with the potential for catastrophe, much like in the highest-grossing film of 1998, Armageddon.

Starring Bruce Willis, Ben Affleck and Liv Tyler, among others, the movie sees NASA scientists discover they have 18 days before an asteroid the size of Texas hits Earth.

They then devise a plan to have a deep core oiler driller (Willis) train a group of asteroids to drill a hole into the space rock so they can detonate a nuclear bomb to split the asteroid in half — the same idea as in Deep Impact, but not one at play with DART.

Ultimately, Willis’ character wants his own men to do the job, including Affleck, and the former has to sacrifice himself to save the planet by making sure the bomb detonates while the others make their escape on the space shuttle they travelled to the asteroid on.

Part of the problem for the fictional scientists in Michael Bay’s film is that they only discovered the asteroid less than three weeks before it was due to hit Earth.

In reality, NASA would know years in advance because it monitors such threats. It considers any near-Earth object ‘potentially hazardous’ if it comes within 0.05 astronomical units (4.6 million miles) and measures more than 460ft in diameter.

More than 27,000 near-Earth asteroids have been catalogued but none currently pose a danger to our planet.

This means that pushing a space rock off course is more of a possibility for DART than it was in Armageddon, where nuclear bombs had to be used to obliterate the giant object.

Deep Impact (pictured) depicts the attempts to prepare for and destroy a 7-mile (11 km) wide asteroid that is set to collide with Earth and cause a mass extinction. A team of astronauts are sent to land on the space rock and drill nuclear bombs deep beneath its surface, but rather than deflect the comet, when they’re detonated they only split it in two. The smaller fragment goes on to hit Earth, creating a megatsunami

Starring Bruce Willis, Ben Affleck and Liv Tyler, among others, Armageddon (pictured) sees NASA scientists discover they have 18 days before an asteroid the size of Texas hits Earth. They then devise a plan to have a deep core oiler driller (Willis) train a group of asteroids to drill a hole into the space rock so they can detonate a nuclear bomb to split the asteroid in half — the same idea as in Deep Impact, but not one at play with DART

With Dimorphos, a small nudge ‘would add up to a big change in its future position, and then the asteroid and the Earth wouldn’t be on a collision course,’ NASA said.

The US space agency’s Bobby Braun added during a media briefing today: ‘This inaugural planetary test mission marks a major moment in human history.

‘For the first time ever we will measurably change the orbit of a celestial body in the universe.

‘Doing so has clear benefits in ensuring humanity’s ability to deflect a potential threatening asteroid in the future.’

Andrea Riley, DART programme executive at NASA HQ, said: ‘The DART demonstration of technology to deflect an asteroid is one we believe is important to conduct before there is an actual need.

‘So while DART’s target does not pose a threat to Earth, this mission and demonstration will give planetary defence experts more confidence that this is a viable mitigation technique should we ever discover [an asteroid that is].’

An asteroid the size of Dimorphos could cause a continent-wide destruction on Earth, while the impact of one the size of the larger Didymos would be felt worldwide.

One of the main reasons for the mission is that although astronomers know in a lot about the orbits of most of the 26,115 currently known near-Earth asteroids, they don’t understand the density of the material the rocks are made of.

This means they can only guess how the surface might behave upon impact, such as from a spacecraft.

Pictured is the SpaceX Falcon 9 rocket which carried DART off the planet when it was launched in November 2021

DART will arrive at Dimorphos in two weeks’ time, where it will deliberately smash into the asteroid at speeds of 15,000mph

DIMORPHOS AND DIDYMOS

Dimorphos completes an orbit around Didymos every 11 hours and 55 minutes. It was discovered in 1996 by the Spacewatch survey at Kitt Peak.

The sub-kilometre asteroid is classified as both a potentially hazardous asteroid and a near-Earth object.

Orbiting Didymos is a ‘moonlet’ called Dimorphos, which was found in 2003.

‘Asteroids are complicated, they look different, they’ve got boulders, they’ve got rocky paths, they’ve got smooth parts,’ Chabot said.

‘And so how exactly the DART spacecraft interacts with a real asteroid of this size and where it hits is one of the main factors for those models and also how that asteroid is put together.

‘We know a lot of asteroids are maybe like rubble piles.’

Scientists constantly search for asteroids and plot their courses to determine whether they could hit the planet.

‘Although there isn’t a currently known asteroid that’s on an impact course with the Earth, we do know that there is a large population of near-Earth asteroids out there,’ said Lindley Johnson, NASA’s Planetary Defense Officer.

‘The key to planetary defence is finding them well before they are an impact threat.

‘We don’t want to be in a situation where an asteroid is headed towards Earth and then have to test this capability.’

NASA is targeting the impact to be as nearly head-on as possible ‘to cause the biggest deflection’, but the 1,210lb spacecraft will not ‘destroy’ the asteroid.

When DART spacecraft smashes into Dimorphos it will also have a witness in the form of an Italian cubesat called LICIACube, or the Light Italian Cubesat for Imaging of Asteroids.

This is a 31lb (14 kg) micro-satellite that has hitched a ride on DART to the Didymos-Dimorphos binary asteroid system, before being deployed yesterday to give it 15 days to assume a safe position to observe the spacecraft’s collision.

‘LICIACube will be released from the dispenser on one of DART’s external panels, and will be guided (braking and rotating) to start its autonomous journey toward Dimorphos,’ Elena Mazzotta Epifani, an astronomer at Italy’s National Institute for Astrophysics (INAF) and a co-investigator on the LICIACube mission, told Space.com.

‘The cubesat will point its cameras toward the asteroid system, but also to DART, and will probably take some pictures of it.’

She added: ‘Together, DART and LICIACube will analyse for the first time and with high detail the physical properties of a binary near-Earth asteroid, allowing us to investigate its nature and have hints on its formation and evolution.

‘LICIACube will obtain multiple images of the ejecta plume produced by the impact itself, of the DART impact [crater] size, as well as the non-impact hemisphere to help us to study the size and morphology of the crater and the effects on the surface properties in the surroundings.’

Both Didymos and the smaller Dimorphos were discovered relatively recently; Didymos in 1996 and the smaller Dimorphos in 2003.

The year it was discovered, Dimorphos came within 3.7 million miles of Earth — 15 times farther away than the moon.

DEFLECTING AN ASTEROID WOULD REQUIRE ‘MULTIPLE BUMPS’, STUDY SAYS

Deflecting an asteroid such as Bennu, which has a small chance of hitting Earth in about a century and a half, could require multiple small impacts from some sort of massive human-made deflection device, according to experts.

Scientists in California have been firing projectiles at meteorites to simulate the best methods of altering the course of an asteroid so that it wouldn’t hit Earth.

According to the results so far, an asteroid like Bennu that is rich in carbon could need several small bumps to charge its course.

Bennu, which is about a third of a mile wide, has a slightly greater chance of hitting Earth than previously thought, NASA revealed earlier this month.

The space agency upgraded the risk of Bennu impacting Earth at some point over the next 300 years to one in 1,750.

Bennu also has a one-in-2,700 chance of hitting Earth on the afternoon of September 24, 2182, according to the NASA study.

Scientists have been seriously considering how to stop an asteroid from ever hitting Earth since the 1960s, but previous approaches have generally involved theories on how to blow the cosmic object into thousands of pieces.

The problem with this is these pieces could potentially zoom towards Earth and present almost as dangerous and humanity-threatening an issue as the original asteroid.

A more recent approach, called kinetic impact deflection (KID), involves firing something into space that more gently bumps the asteroid off course, away from Earth, while keeping it intact.

Recent KID efforts were outlined at the 84th annual meeting of the Meteoritical Society held in Chicago this month and led by Dr George Flynn, a physicist at State University of New York, Plattsburgh.

‘You might have to use multiple impacts,’ Dr Flynn said in conversation with The New York Times. ‘It [Bennu] may barely miss, but barely missing is enough.’

Researchers have been working at NASA’s Ames Vertical Gun Range, built in the 1960s during the Apollo era and based at Moffett Federal Airfield in California’s Silicon Valley, for the recent KID experiments.

They fired small, spherical aluminum projectiles at meteorites suspended by pieces of nylon string.

The team used 32 meteorites – which are fragments of asteroids that have fallen to Earth from space – that were mostly purchased from private dealers.

The tests have allowed them to work out at what point momentum from a human-made object fired towards an asteroid turns it into thousands of fragments, rather than knocking it off course as desired.

‘If you break it into pieces, some of those pieces may still be on a collision course with Earth,’ Dr Flynn said.

Carbonaceous chondrite (C-type) asteroids, such as Bennu, are the most common in the solar system.

They are darker than other asteroids due to the presence of carbon and are some of the most ancient objects in the solar system – dating back to its birth.

According to the findings from experiments at AVGR, the type of asteroid being targeted (and how much carbon it has in it) may dictate how much momentum would be directed at it from any human-made KID device.

From the experiments, the researchers found C-type meteorites could withstand only about one-sixth of the momentum that the other chondrites could withstand before shattering.

‘[C-type] asteroids are much more difficult to deflect without disruption than ordinary chondrite asteroids,’ the experts concluded.

‘These results indicate multiple successive impacts may be required to deflect rather than disrupt asteroids, particularly carbonaceous asteroids.’

Therefore, around 160 years in the future – when Bennu is most likely to collide with Earth, according to NASA – a KID device would have to give it a series of gentle nudges to prevent it from breaking up and sending dangerous splinter fragments flying towards Earth.

NASA’s recent study about Bennu, published in the journal Icarus, did point out there is more than a 99.9 per cent probability Bennu will not smash into Earth over the next three centuries.

‘Although the chances of it hitting Earth are very low, Bennu remains one of the two most hazardous known asteroids in our solar system, along with another asteroid called 1950 DA,’ NASA said in a statement.