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On Monday, a NASA spacecraft will deliberately collide with an asteroid called Dimorphos.
The Double Asteroid Redirection Test mission, or DART, aims to see if this type of kinetic impact can help deflect an asteroid that poses a threat to Earth.
“We’re moving an asteroid,” said Tom Statler, NASA’s program scientist for the DART mission. “We are changing the movement of a natural celestial body in space. Humanity has never done that 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 in the asteroid system on September 26. Impact is expected at 7:14 pm ET.
The spacecraft is headed for a double asteroid system, where a small “moon” asteroid, called Dimorphos, orbits a larger asteroid, Didymos.
Didymus. meaning “twin” in Greek, it measures approximately 780 meters (2,560 feet) in diameter. Dimorphos, meanwhile, is 525 feet (160 meters) across, and its name means “two forms.”
At impact, Didymos and Dimorphos will be relatively close to Earth, within 6.8 million miles (11 million km).
Neither Dimorphos nor Didymos are at risk of colliding with Earth, before or after the collision occurs.
DART is going down in a blaze of glory. He will set his sights on Dimorphos, speed up to 13,421 miles per hour (21,600 kilometers per hour), and hit the moon almost head-on.
The spacecraft is about 100 times smaller than Dimorphos, so it won’t destroy the asteroid.
Instead, DART will attempt to change the speed and trajectory of the asteroid in space. The mission team has likened this collision to a golf cart hitting one of the Great Pyramids – enough energy to leave an impact crater.
The impact will change Dimorphos’ speed by 1% while orbiting Didymos. It doesn’t sound like much, but doing so will change the moon’s orbital period.
The push will slightly shift Dimorphos and make it more gravitationally bound 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.
The spacecraft will share its view of the double-asteroid system through an instrument known as the Didymos Asteroid and Reconnaissance Camera for Optical Navigation, or DRACO.
This imager, which serves as DART’s eyes, will allow the spacecraft to identify the double-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 transmit back to Earth at a rate of one image per second in what will appear almost like a video. You can watch the live stream at NASA websitestarting at 6 p.m. ET on Monday.
Didymos and Dimorphos will appear as points of light about an hour before impact, gradually increasing in size and with more detail in the frame.
Dimorphos has never been observed before, so scientists can finally appreciate its shape and surface appearance.
We should be able to see Dimorphos in exquisite detail before DART crashes into him. Given the time it takes for the images to be transmitted back to Earth, they will be visible for eight seconds before a loss of signal occurs and the DART mission, if successful, ends.
The spaceship too he has his own photojournalist along for the ride.
A briefcase-sized satellite of the Italian Space Agency traveled into space with DART. Called the Light Italian CubeSat for Imaging of Asteroids, or LICIACube, it separated from the spacecraft on September 11. The satellite travels behind DART to record what’s happening from a safe perspective.
Three minutes after impact, LICIACube will fly over Dimorphos to capture images and video of the impact column. and maybe even spy on the impact crater. The CubeSat will rotate to keep its cameras pointed at Dimorphos as it flies by.
The images and video, although not immediately available, will be transmitted to Earth in the days and weeks after the collision.
The LICIACube will not be the only observer watching. The James Webb Space Telescope, the Hubble Space Telescope and NASA’s Lucy mission will observe the impact. The Didymos system may glow as its dust and debris are expelled into space, said Statler, a NASA program scientist.
But ground-based telescopes will be key to determining whether DART successfully changed Dimorphos’ motion.
The Didymos system was discovered in 1996, so astronomers have many observations of the system. After the impact, observatories around the world will watch as Dimorphos crosses in front of and moves behind Didymos.
Dimorphos takes 11 hours and 55 minutes to complete one orbit of Didymos. If DART is successful, that time could drop by 73 seconds, “but we actually think we’re going to change it in about 10 minutes,” said Edward Reynolds, DART project manager at the Johns Hopkins University Applied Physics Laboratory.
Statler said he would be surprised if a period change measurement came in less than a few days, but even more so if it took more than three weeks.
“I’m very confident that we were going to get there on Monday and it would be a complete success,” said Lindley Johnson, NASA’s planetary defense officer.
But if DART loses its proverbial dartboard, the team will be ready to ensure the spacecraft is safe and all its data is downloaded to find out why it didn’t hit Dimorphos.
The Applied Physics Laboratory Mission Operations Center will step in if necessary, although 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 it has rehearsed, said Elena Adams, a DART mission systems engineer at the Applied Physics Laboratory.
Dimorphos was chosen for this mission because its size is comparable to that of 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 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 an orbit that puts them within 48.3 million kilometers (30 million miles) of Earth. Detecting the threat of near-Earth objects that could cause serious damage is a primary focus of NASA and other space organizations around the world.
No asteroids are currently on a direct impact course with Earth, but there are more than 27,000 near-Earth asteroids in all shapes and sizes.
The valuable data collected by DART will contribute to planetary defense strategies, especially understanding what kind of force can change the orbit of a near-Earth asteroid that could collide with our planet.
Films make the fight against asteroid approaches look like a hasty fight to protect the planet, but “That’s not the way to do a planetary defense,” Johnson said. Exploding an asteroid could be more dangerous because then its pieces could be on a collision course with Earth.
But NASA is considering other methods to change the motion of asteroids.
The DART spacecraft is considered a kinetic impactor that could change Dimorphos’ speed and trajectory. If DART is successful, it could be a tool to deflect asteroids.
Another option is a gravity tractor, which relies on the mutual gravitational pull between a spacecraft and an asteroid to pull the space rock out of its impact path and into a more benign one, Johnson said.
Another technique is ion beam deflection, or firing an ion engine at an asteroid for long periods of time until the ions change the speed and orbit of the asteroid.
But both take time.
“Any technique you can imagine that changes the orbital speed 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 for deflecting an asteroid, based on its size and trajectory.
Finding populations of dangerous asteroids and determining their sizes are top priorities for NASA and its international partners, Johnson said. The design of a space-based telescope called Near Earth Object Surveyor Mission is currently under review.
The Didymos system will not be alone for long. To assess the consequences of the impact, the European Space Agency’s Hera mission will launch in 2024. The spacecraft, along with two CubeSats, will arrive at the asteroid system two years later.
Hera will study both 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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