Asteroids Dimorphos and Didymos, Florida, September 26, 2022 (Jim Watson/AFP)
Sooner or later, humanity will spot an asteroid heading toward Earth capable of destroying a city or even an entire country. For this reason, in 2022, NASA conducted an experiment similar to a rehearsal for defending the planet, as it deliberately collided with an unmanned spacecraft with a non-dangerous asteroid to change its course.
The target was a small object about 525 feet long called Dimorphos, a small moon orbiting a larger asteroid about 2,550 feet long known as Didymos. Neither poses a threat to Earth, and changing the orbit of the smaller asteroid around its larger companion was unlikely to change that.
NASA’s mission, known as the Double Asteroid Redirection Test (DART), succeeded in proving the possibility of removing an asteroid from Earth through an intentional collision.
But careful observations conducted using telescopes on the two asteroids have now revealed that the powerful collision carried out by DART with Demorphos was so violent that the bounce of the small moon created a gravitational push on the larger asteroid Didymos, which led to changing the path of the two asteroids together around the sun.
In other words, “When we hit the small moon with that force, we also moved the large body next to it a little bit,” says Andy Rifkin, a planetary astronomer at the Johns Hopkins University Applied Physics Laboratory and one of the authors of the new study published March 6 in the journal Science Advances. This is the first time humanity has changed the orbit of an asteroid orbiting the sun.
Binary asteroids, such as Didymos and Demorphos, share a single center of gravity. This center is dominated by the largest body in mass, in this case Didymos, whose mass is approximately 200 times greater than its small moon. However, if the smaller body is subjected to a strong shock, the larger body will also feel its impact.
Before the DART spacecraft collides with Dimorphos in 2022, scientists were forced to study all possible outcomes of the mission, including some very disturbing scenarios.
“What if this experiment puts the Didymos system on a collision course with Earth? This is of course undesirable, so we considered this possibility,” said Rahel Macadia, one of the study’s participants and a planetary defense researcher at the University of Illinois. Scientists then concluded that there would be no detectable effect on Didymos; He may feel the impact of the collision on Demorphos, but he will not move from his place.
At the time, NASA believed that for the mission to be successful, Dimorphos’ orbit around Didymos would be required to change by only 73 seconds. But the small vehicle, approximately the size of a truck, succeeded in reducing the asteroid’s orbit by about 33 minutes, thanks to the force of the collision and the large explosion of rocky debris that was scattered from “Dimorphos” at the moment of impact.
Before the mission was carried out, astronomers believed that “Dimorphos” was what is known as a “rubble pile”, meaning that it was not one huge solid rock, but rather more like a group of large rocks barely held together by weak gravity. When a spacecraft collided with it at a speed of 14,000 miles per hour, it was expected that part of these rocks would scatter into space.
