The DART mission is about to collide with an asteroid


The Double Asteroid Redirection Test, or DART, mission aims to see if this kind of kinetic impact can help deflect an asteroid threatening Earth.

“We’re moving an asteroid,” said Tom Statler, NASA program scientist for the DART mission. “We are altering the motion of a natural celestial body in space. Humanity has never done this before.”

Here’s what you need to know about this mission.

The DART spacecraft is about the size of a school bus. It has been traveling to reach its asteroid target since its launch in November 2021. The spacecraft will arrive at the asteroid system on September 26. Impact is expected at 7:14 p.m. ET.

Where is he going ?

The spacecraft is heading towards a twin asteroid system, where a tiny “lunar” asteroid, named Dimorphos, orbits a larger asteroid, Didymos.

Didymos. which means “twin” in Greek, is approximately 2,560 feet (780 meters) in diameter. Meanwhile, Dimorphos is 525 feet (160 meters) in diameter and its name means “two forms”.

At the time of impact, Didymos and Dimorphos will be relatively close to Earth – within 6.8 million miles (11 million kilometers).

Neither Dimorphos nor Didymos are risk of colliding with the Earth – before or after the collision.

What will DART do?

DART falls in a burst of glory. It will target Dimorphos, accelerate to 13,421 miles per hour (21,600 kilometers per hour) and crash into the moon almost head-on.

The spaceship is about 100 times smaller than Dimorphos, so it won’t obliterate the asteroid.

Instead, DART will try to alter the asteroid’s speed and trajectory through space. The mission team likened this collision to a golf cart crashing into one of the Great Pyramids – enough energy to leave an impact crater.

The impact will change Dimorphos’ speed by 1% as it orbits Didymos. That doesn’t sound like much, but it will change the moon’s orbital period.

The nudge will displace Dimorphos slightly and make him more gravitationally bound to Didymos – so the collision won’t change the binary system’s trajectory around Earth or increase its chances of becoming a threat to our planet.

What are we going to see?

The spacecraft will share its view of the twin asteroid system through an instrument known as the Didymos Reconnaissance and Asteroid Camera for Optical navigation, or DRACO.

This imager, which serves as the eyes of DART, will allow the spacecraft to identify the twin asteroid system and distinguish which space object it is supposed to hit.

This instrument is also a high-resolution camera that aims to capture images of the two asteroids to send back to Earth at a rate of one frame per second in what will almost look like video. You can watch the live stream on NASA’s website, starting at 6 p.m. ET Monday.

Didymos and Dimorphos will appear as points of light about an hour before impact, gradually becoming larger and more detailed in frame.

Dimorphos has never been observed before, so scientists can finally grasp its shape and surface appearance.

We should be able to see Dimorphos in exquisite detail before DART crashes into it. Given the time it takes for the images to return to Earth, they will be visible for eight seconds before a loss of signal occurs and the DART mission ends – if successful.

The spaceship too has its own photojournalist for the ride.

A briefcase-sized satellite from the Italian Space Agency hitchhiked with DART in space. Called the Light Italian CubeSat for Imaging of Asteroids, or LICIACube, it detached from the spacecraft on September 11. The satellite moves behind DART to record what is happening from a safe vantage point.

Three minutes after impact, LICIACube will fly over Dimorphos to capture images and video of the impact plume and maybe even spy on the impact crater. The CubeSat will turn to keep its cameras pointed at Dimorphos as it passes.

Images and video, although not immediately available, will be broadcast back to Earth in the days and weeks following the collision.

How will we know if the mission was a success?

The LICIACube will not be the only observer to observe. The James Webb Space Telescope, Hubble Space Telescope and NASA’s Lucy Mission will observe the impact. The Didymos system may brighten as its dust and debris are ejected into space, said Statler, the NASA program scientist.

But ground-based telescopes will be key to determining whether DART succeeded in altering Dimorphos’ motion.

The Didymos system was discovered in 1996, so astronomers have plenty of observations of the system. After impact, observatories around the world will see Dimorphos crossing ahead and moving behind Didymos.

Dimorphos takes 11 hours and 55 minutes to orbit Didymos. If DART is successful, that time could drop to 73 seconds, “but we actually think we’re going to change it by about 10 minutes,” said Edward Reynolds, DART project leader at the Johns Hopkins University Applied Physics Laboratory. .

Statler said he would be surprised if a measurement of the period change came in less than a few days, but even more so if it took longer than three weeks.

What if DART misses and doesn’t hit the asteroid?

“I’m very confident that we’re going to strike on Monday, and it will be a complete success,” said Lindley Johnson, NASA planetary defense officer.

But if DART misses its proverbial dartboard, the team will be ready to make sure the spacecraft is safe and all of its information is downloaded to figure out why it didn’t hit Dimorphos.

The Applied Physics Laboratory’s Mission Operations Center will intervene if necessary, even though DART will have been operating autonomously for the last four hours of its journey.

It takes 38 seconds for a command to travel from Earth to the spacecraft, so the team can react quickly. The DART team has 21 contingency plans that they’ve rehearsed, said Elena Adams, DART mission systems engineer at the Applied Physics Lab.

Why do we need to test this, and why on this asteroid?

Dimorphos was chosen for this mission because it is comparable in size to asteroids that could pose a threat to Earth. A Dimorphos-sized asteroid could cause “regional devastation” if it hits Earth.

The asteroid system is “the perfect natural laboratory” for the test, Statler said.

The mission will give scientists a better understanding of the size and mass of each asteroid, which is crucial for understanding near-Earth objects.

Near-Earth objects are asteroids and comets whose orbit places them within 48.3 million kilometers of Earth. Detecting the threat of near-Earth objects with the potential to cause serious damage is one of the primary goals of NASA and other space organizations around the world.

No asteroids are currently on a direct impact path with Earth, but more than 27,000 near-Earth asteroids exist in all shapes and sizes.

The valuable data collected by DART will aid in planetary defense strategies, particularly in understanding what kind of force can shift the orbit of a near-Earth asteroid that could collide with our planet.

Why not just blow up the asteroid, like in ‘Armageddon’?

Movies make the fight against approaching asteroids feel like a hasty race to protect the planet, but “That’s not the way to do planetary defense,” Johnson said. Blowing up an asteroid could be more dangerous because its pieces could then collide with Earth.

But NASA is considering other methods to alter the motion of asteroids.

The DART spacecraft is believed to be a kinetic impactor that could alter the speed and trajectory of Dimorphos. If DART is successful, it could be a tool to deflect asteroids.

Another option is a gravity tractor, which relies on the mutual gravitational attraction between a spacecraft and an asteroid to pull space rock from its impact path to a more benign path, Johnson said.

Another technique is ion beam deflection or firing an ion engine at an asteroid for long periods of time until the ions alter the asteroid’s speed and orbit.

But both take time.

“Any technique you can imagine that changes the orbital velocity of the orbiting asteroid is a viable technique,” Johnson said.

An international forum called the Space Planning Commission brought together 18 national space agencies to assess what might be best to deflect an asteroid, given its size and trajectory.

Finding populations of dangerous asteroids and determining their size are priorities for NASA and its international partners, Johnson said. The design of a space telescope called the Near-Earth Object Surveyor mission is currently under review.

Will other spacecraft fly by Dimorphos in the future?

The Didymos system will not be alone for too long. To study the aftermath of the impact, the European Space Agency’s Hera mission will be launched in 2024. The spacecraft, along with two CubeSats, will arrive at the asteroid system two years later.

Hera will study the two asteroids, measure the physical properties of Dimorphos, and examine the DART impact crater and the Moon’s orbit, with the goal of establishing an effective planetary defense strategy.


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