Planetary defence focuses on large-ish asteroids that could theoretically crash into Earth, and what humans could do to protect ourselves. One method of protecting our planet is to crash into an asteroid hard enough while it’s far enough away from Earth, to bump it off course.
However, knowing the best way to do slam into an asteroid can be tricky, so that’s where DART comes into play. Its first target isn’t a threat to Earth, but by examining it carefully and then colliding with it, Nancy Chabot, a planetary scientist at Johns Hopkins University’s Applied Physics Laboratory and project scientist for DART in addition to the rest of the DART team will use it to create the data humans will need if they ever want to redirect an asteroid that is indeed on a collision course with Earth.
This mission is very different from the other asteroid missions that have made the news this year, like NASA’s OSIRIS-REx and Japan’s Hayabusa2. These missions each made strides toward tapping near-Earth asteroids to gather samples to bring back to our planet. Scientists hope those samples will help them learn more about the solar system’s earliest days.
DART’s target is an asteroid called Didymos, which was selected based on very different criteria. It’s a binary asteroid, which means DART can slam into the smaller object of the pair. But scientists can collect useful data about the bodies and their locations from Earth, which will help them track where to target the car-size spacecraft in addition to how much the collision bumped the object off course.
Moreover, there’s the impact itself, as the spacecraft slams itself into the space rock at a speed of nearly 13,500 mph (6 kilometres per second). If the mission launches as planned in June 2021, that test crash will come in October 2022.
While ground telescopes will track how the tango of Didymos’ two parts changes after the impact, scientists could also rely on two eyewitnesses.
The first is a cubesat, known as the Light Italian Cubesat for Imaging of Asteroids, which the Italian space agency has proposed to send with DART. The second is a European Space Agency mission known as Hera, which it is thinking about launching in time for it to arrive at Didymos in 2026. That spacecraft would be able to examine the binary asteroid in more detail and measure the crater DART creates.
Chabot said that to date, people appear to be excited and on board with the idea of slamming a spacecraft into an asteroid, in case it needs to be done for real. However, she also said that we can learn only so much from the experiment and that if an asteroid does pose a threat to Earth, we’ll need a heads-up. Thus, continuing to observe and identify asteroids is essential.