The Double Asteroid Redirection Test mission, or DART, aims to test whether this kind of kinetic impact can help redirect an Earth-threatening asteroid.
“We’re moving an asteroid,” said Tom Statler, NASA program scientist for the DART mission. “We are changing 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 reach the asteroid system on September 26. Kickoff is expected at 7:14 PM ET.
Where is it going?
The spacecraft is headed for a double asteroid system in which a small “moon” asteroid called Dimorphos orbits a larger asteroid, Didymos.
Didymos. means “twin” in Greek, about 2,560 feet (780 meters) in diameter. Meanwhile, Dimorphos measures 525 feet (160 meters) wide, and its name means “two forms.”
On impact, Didymos and Dimorphos will be relatively close to Earth — within 6.8 million miles (11 million kilometers).
Neither Dimorphos nor Didymos Risk of collision with ground — before or after collision.
What will DART do?
DART goes down in a blaze of glory. It will focus on Dimorphos, accelerate to 13,421 miles per hour (21,600 kilometers per hour) and crash almost head-on into the Moon.
The spacecraft is about 100 times smaller than Dimorphos, so it won’t destroy the asteroid.
Instead, DART will try to change the asteroid’s speed and path in space. The mission team compared the impact to a golf cart crashing into one of the Great Pyramids — enough energy to leave the impact crater.
The hit will change Dimorphos’ speed by 1% in Didymos’ orbit. It doesn’t sound like much, but doing so will change the moon’s orbital period.
The button will slightly alter Dimorphos, binding it more gravitationally to Didymos — so the collision won’t change the binary system’s path around Earth or increase its chances of becoming a threat to our planet.
What will we see?
The spacecraft will share its view of the twin asteroid system through an instrument known as the Didymos Reconnaissance and Asteroid Camera, or DRACO, for optical navigation.
Acting as DART’s eye, this imaging device will allow the spacecraft to identify the double asteroid system and distinguish which space object it should hit.
Didymos and Dimorphos will appear as pins of light about an hour before impact, gradually growing larger and more detailed in the frame.
Dimorphos has never been observed before, so scientists can finally get its shape and surface appearance.
We should be able to see Dimorphos in fine detail before the DART hits him. Given the time it takes for the images to return to Earth, they will be visible for eight seconds before signal loss occurs and DART’s mission ends — if it’s successful.
Spaceship too has its own photojournalist for the ride.
The Italian Space Agency’s briefcase-sized satellite has been launched into space by DART. Called the Lightweight Italian CubeSat, or LICIACube, for asteroid imaging, it left the spacecraft on September 11. The satellite travels behind DART to record what’s happening from a safe perspective.
Three minutes after impact, the LICIACube will fly by Dimorphos to capture images and video of the impressive plume. and maybe spy an impact crater. The CubeSat will rotate to focus its cameras on Dimorphos as it flies.
Although the images and videos are not immediately available, they will be sent back to Earth in the days and weeks after the collision.
How will we know if there is a mission? was it successful?
LICIACube won’t be the only observer watching. The James Webb Space Telescope, the Hubble Space Telescope and NASA’s Lucy mission will observe the impact. Statler, a NASA program scientist, said the Didymos system could brighten as dust and debris are ejected into space.
But ground-based telescopes will play a key role in determining whether DART successfully alters Dimorphos’ motion.
The Didymos system was discovered in 1996, so astronomers have made many observations about the system. After impact, observatories around the world will watch as Dimorphos passes in front of and moves behind Didymos.
Dimorphos takes 11 hours and 55 minutes to complete an orbit of Didymos. If DART is successful, that time could be reduced by 73 seconds, “but we actually think we’ll change it by about 10 minutes,” said Edward Reynolds, DART project manager at Johns Hopkins University’s Applied Physics Laboratory.
Statler said he would be more surprised if the period change was measured in less than a few days, but if it took more than three weeks.
What if the DART misses and doesn’t hit the asteroid?
“I’m very confident that we will hit on Monday and it will be a complete success,” said Lindley Johnson, NASA’s planetary defense officer.
But if DART misses its proverbial dartboard, the team will be ready to ensure that the spacecraft is safe and that all of its data is downloaded to figure out why it didn’t hit Dimorphos.
The Applied Physics Laboratory’s Mission Operations Center will intervene if necessary, although DART will operate autonomously during the final four hours of its journey.
It takes 38 seconds for the team to get from Earth to the spacecraft so the team can react quickly. Elena Adams, a DART mission systems engineer at the Applied Physics Laboratory, said the DART team has 21 contingency plans that it has practiced.
Why should we test this and why on this asteroid?
Dimorphos was chosen for this mission because its size is comparable to asteroids that could pose a threat to Earth. An asteroid the size of Dimorphos could cause “regional devastation” if it were to hit Earth.
The asteroid system is a “perfect natural laboratory” for testing, Statler said.
The mission will allow scientists to better understand the size and mass of each asteroid, which is crucial for understanding near-Earth objects.
Near-Earth objects are asteroids and comets with orbits that place them within 30 million miles (48.3 million kilometers) of Earth. Detecting the threat of near-Earth objects that can cause serious damage is a major focus of NASA and other space agencies around the world.
No asteroids are currently on a direct collision course with Earth, but there are over 27,000 near-Earth asteroids of all shapes and sizes.
The valuable information collected by DART will help planetary defense strategies, especially understanding what force might change the orbit of a near-Earth asteroid that could collide with our planet.
Why don’t we blow up an asteroid like in Armageddon?
Movies asteroid-fighting approaches seem like a hasty scramble to protect the planet, but “This is not the way to do planetary defense,” Johnson said. Blowing up an asteroid would be more dangerous because then its fragments would be on a collision course with Earth.
But NASA is considering other ways to change the motion of asteroids.
The DART spacecraft is considered a kinetic effector capable of changing Dimorphos’ speed and path. If DART is successful, it could be a tool to redirect asteroids.
Another option, Johnson said, is a gravity tractor that relies on the mutual gravitational force between the spacecraft and the asteroid to pull the space rock out of the impact trajectory.
Another method is to bend the ion beam, or shoot an ion thruster at the asteroid for a long time until the ions change the asteroid’s speed and orbit.
But both of these take time.
“Any technique that you can imagine changing the orbital velocity of an asteroid in orbit is a viable technique,” Johnson said.
An international forum called the Space Planning Commission brought together 18 national space agencies to evaluate the best option for redirecting an asteroid, depending on its size and path.
Will other spacecraft fly through Dimorphos in the future?
The Didymos system will not be alone for very long. The European Space Agency’s Hera mission will launch in 2024 to investigate the impact. The spacecraft, along with two CubeSats, will reach the asteroid system in two years.
Hera will both study asteroids, measure the physical properties of Dimorphos, and explore the DART impact crater and the moon’s orbit in order to develop an effective planetary defense strategy.
