NASA’s Planetary Defense Mission will test asteroid deflection, but how realistic is that?

On September 26, NASA will crash a spacecraft into an asteroid to interrupt its path. A space rock is not predicted to hit Earth, nor is it predicted to hit any other known asteroid or large object. Collision is a test – the essence of NASA’s Double Asteroid Redirect Test (DART) mission. While there is no actual impending collision, the DART mission accurately mimics what NASA scientists would do if an asteroid was heading towards Earth. The mission will also provide scientists with valuable data to help them better prepare to redirect a large asteroid or comet should they head towards us.

“This is 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 mission co-investigator, told

The DART mission is specifically testing a technique called the kinetic deflector technique, which is basically colliding a spacecraft with an asteroid to try to divert or redirect its path away from Earth. Its target is the satellite Dimorphos, which orbits the larger asteroid Didymos. At 525 feet (160 meters) in diameter, Jacobson said Dimorphos is exactly the size of an asteroid that scientists would actually try to redirect with a kinetic impactor, since the asteroid would be large enough that simple evacuation measures would not be practical. , but small enough that only a moving object can deflect it. This strategy would be especially useful if we knew about the impact less than a few decades before it happens, he says.

Related: NASA’s DART asteroid impact mission to be key planetary defense test

While an object the size of Dimorphos would cause serious damage if it hit Earth, it probably wouldn’t pose a danger to the entire planet. By comparison, the asteroid Chicxulub, which caused the extinction of the non-Avian dinosaurs, was about 6 miles (10 km) in diameter. To deflect anything close to that size, we would need a nuclear bomb or other powerful explosive device attached to a kinetic impactor, Jacobson says. It will also take us a long time, ideally many decades, to develop such a missile, he said. But even with such a large object, the basic idea is the same as in DART: imparting momentum to the object by colliding something with it and redirecting it.

“We really need to understand this technique first before you can imagine adding an explosive,” Jacobson said.

The mission also demonstrates the high level of international cooperation required to plan and execute a kinetic near-Earth object impact. While the mission is being 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 the exact orbit of Dimorphos around Didymos and evaluating the success of the mission.

“We have been working very closely with our European counterparts and colleagues around the world,” Ellen Howell, senior scientist at the University of Arizona Lunar and Planetary Laboratory and DART co-investigator, told While DART is a test, she said, a similar level of international cooperation will be needed if there is a real impact.

Of course, there are a few key differences between DART and real asteroid impact protection. The biggest one is that none of the asteroids in the chosen system will collide with the Earth. The scientists chose the Didymos system because it’s a so-called eclipsing binary when viewed from Earth — in other words, Dimorphos noticeably passes in front of Didymos, obscuring it. This obscuration allows scientists to accurately measure how long it takes the smaller asteroid to orbit the larger one, and measure how much that time period will change after the DART spacecraft collides with Dimorphos. Scientists will use this information to find out how much momentum the spacecraft is imparting to the asteroid, and this information will be critical if we ever really need to use the technique, Jacobson said.

Also, the real target will almost certainly not be part of a binary system, Howell said, and neither will very few asteroids. In addition, the risk of any object of this size or larger colliding with the Earth in the near future is extremely small. NASA says there is nothing to worry about, at least for the next century.

However, NASA’s Planetary Defense Coordination Office takes the risk of near-Earth object impact very seriously, just as many people study and try to mitigate the effects of earthquakes, tsunamis and volcanic eruptions, Jacobson said.

“These are all natural disasters,” he said. “While you can never completely eliminate the possibility of them occurring, you can definitely mitigate their impact and try to avoid the worst-case scenario.”

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