On September 26, NASA will crash a spacecraft into an asteroid to interrupt its path. Space rock is not expected to collide with Earth, nor are any others known asteroid or large object. Impact is a test, the crux of NASA’s Double Asteroid Redirection Test (DART) mission. While there is no real impending collision, the DART mission closely mimics what NASA scientists would do if an asteroid headed towards Earth. The mission will also provide scientists with valuable data that will better prepare them to redirect a large asteroid or comet if one were to go towards us.
“It’s exactly the kind of mission we would use to actually deflect an asteroid,” Seth Jacobson, assistant professor of planetary science at Michigan State University and co-investigator of the mission, told Space.com.
The DART mission is specifically testing a method called the kinetic deflector technique: basically, crashing a spacecraft into an asteroid to try to deflect or redirect its path away from Land. Its target is the moon Dimorphos, which orbits the largest asteroid didimo. With a diameter of 525 feet (160 meters), Dimorphos is exactly the size of an asteroid that scientists would really try to redirect with a kinetic impactor, Jacobson said, since the asteroid would be large enough for simple evacuation measurements. they wouldn’t be practical, but small enough that a moving object alone could be able to deflect it. The strategy would be particularly useful, he said, if we discovered the impact less than a few decades before it happened.
Related: NASA’s DART asteroid impact mission will be a key test for planetary defense
Although an object the size of Dimorphos would cause severe damage if it were to hit Earth, it probably wouldn’t be a danger to the entire planet. For comparison, the asteroid Chicxulub, which triggered the extinction of non-avian dinosaurs, was about 6 miles (10 km) in diameter. To deflect something like those dimensions, we would need a nuclear bomb or other powerful explosive attached to the kinetic impactor, Jacobson said. We would also need a long time, ideally several decades, to develop such a missile, he said. But even with such a large object, the basic idea is the same as in DART: to transfer momentum to the object by crashing it into something and redirecting it.
“We need to understand this technique first, before you can imagine adding an explosive component,” Jacobson said.
The mission also demonstrates the high level of international collaboration required to plan and execute a kinetic impact with a near-Earth object. Although the mission is led by NASA and the Johns Hopkins University Applied Physics Laboratory, scientists and engineers from around the world are contributing to DART, for example by calculating Dimorphos’ precise orbit around Didymos and measuring the success of the mission.
“We have worked closely with our European colleagues and colleagues around the world,” Ellen Howell, senior researcher at the University of Arizona Lunar and Planetary Laboratory and co-investigator of DART, told Space.com. Although DART is a test, a similar level of international cooperation would be essential in the event of a real impact, she said.
Of course, there are some key differences between DART and a defense against a true asteroid impact. The biggest is that neither of the two asteroids in the chosen system are expected to hit Earth. Scientists chose the Didymos system because it is a so-called eclipsing track when viewed from Earth: in other words, Dimorphos visibly passes in front of Didymos, attenuating it. This obscuration allows scientists to accurately measure how long it takes the smaller asteroid to orbit the larger one, and to measure how much that time period changes once the DART spacecraft collides with Dimorphos. Scientists will use this information to find out how much momentum the spacecraft transfers to the asteroid, which is information that will be crucial if we ever really need to use this technique, Jacobson said.
Furthermore, a true target would almost certainly not be part of a binary system, Howell said, as very few asteroids are. Furthermore, the risk of any object of this size or larger having an impact on Earth in the near future is extremely small. NASA says so there is nothing to worry about at least for the next century.
However, NASA’s Office of Planetary Defense Coordination takes the risk of impacting near-Earth objects very seriously, in the same way that many people study and try to mitigate the effects of earthquakes, tsunamis and volcanic eruptions, it has Jacobson said.
“These are all things that are natural hazards,” he said. “While you can never completely get rid of the possibility of them happening, you can definitely mitigate their impact and try to avoid the worst case scenario.”
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