The DART mission, or the Double Asteroid Redirection Test, will have a rendezvous with the space rock on September 26 after launching 10 months ago.
The event will be the agency’s first full-scale demonstration of deflection technology that can protect the planet.
“For the first time ever, we will measurably change the orbit of a celestial body in the universe,” said Robert Braun, head of the Johns Hopkins University Applied Physics Laboratory’s Space Exploration Sector.
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, or NEOs, that could cause grave harm is a primary focus of NASA and other space organizations around the world.
Astronomers discovered Didymos more than two decades ago. It means “twin” in Greek, a nod to how the asteroid forms a binary system with the smaller asteroid, or moon. Didymos is nearly half a mile (0.8 kilometer) across.
Meanwhile, Dimorphos is 525 feet (160 meters) in diameter, and its name means “two forms.”
The spacecraft recently caught its first glimpse of Didymos using an instrument called the Didymos Reconnaissance and Asteroid Camera for Optical navigation, or DRACO. It was about 20 million miles (32 million kilometers) away from the binary asteroid system when it took images in July.
On the day of impact, images taken by DRACO will not only reveal our first look at Dimorphos, but the spacecraft will use them to autonomously guide itself for an encounter with the tiny moon.
During the event, these images will stream back to Earth at a rate of one per second, providing a “pretty stunning” look at the moon, said Nancy Chabot, planetary scientist and DART coordination lead at the Applied Physics Laboratory.
At the time of impact, Didymos and Dimorphos will be relatively close to Earth — within 6.8 million miles (11 million kilometers).
The spacecraft will accelerate at about 15,000 miles per hour (24,140 kilometers per hour) when it collides with Dimorphos.
It aims to crash into Dimorphos to change the asteroid’s motion in space, according to NASA. This collision will be recorded by LICIACube, or Light Italian CubeSat for Imaging of Asteroids, a companion cube satellite provided by the Italian Space Agency.
The briefcase-size CubeSat hitched a ride with DART into space. It recently deployed from the spacecraft and is traveling behind it to record what happens.
Three minutes after impact, the CubeSat will fly by Dimorphos to capture images and video. The video, while not immediately available, will be streamed back to Earth in the weeks and months following the collision.
Protecting the planet
Dimorphos was chosen for this mission because its size is relative to asteroids that could pose a threat to Earth. The spacecraft is about 100 times smaller than Dimorphos, so it won’t obliterate the asteroid.
The fast impact will only change Dimorphos’ speed as it orbits Didymos by 1%, which doesn’t sound like a lot — but it will change the moon’s orbital period.
“Sometimes we describe it as running a golf cart into a great pyramid or something like that,” Chabot said. “But for Dimorphos, this really is about asteroid deflection, not disruption. This isn’t going to blow up the asteroid; it isn’t going to put it into lots of pieces.”
The nudge will shift Dimorphos slightly and make it more gravitationally bound to Didymos — so the collision won’t change the binary system’s path around the Earth or increase its chances of becoming a threat to our planet, Chabot said.
Dimorphos completes an orbit around Didymos every 11 hours and 55 minutes. After the impact, that may change to 11 hours and 45 minutes, but follow-up observations will determine how much of a shift occurred.
Astronomers will use ground-based telescopes to observe the binary asteroid system and see how much the orbital period of Dimorphos changed, which will determine if DART was successful.
Space-based telescopes such as Hubble, Webb and NASA’s Lucy mission will also observe the event.
In four years, the European Space Agency’s Hera mission will arrive to study Dimorphos, measuring physical properties of the moon, and look at the DART impact and the moon’s orbit.
No asteroids are currently on a direct impact course with Earth, but more than 27,000 near-Earth asteroids exist in all shapes and sizes.
The valuable data collected by DART and Hera will contribute to planetary defense strategies, especially the understanding of what kind of force can shift the orbit of a near-Earth asteroid that could collide with our planet.