NASA accidentally changed the asteroid's orbit around the Sun for the first time

Sooner or later, humanity will discover an asteroid approaching us that is capable of destroying an entire city or even an entire country. That is why in 2022, NASA conducted a dress rehearsal for planetary defense: they deliberately crashed an unmanned spacecraft into a harmless asteroid to change its trajectory, writes UNN with reference to National Geographic. 

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The target was the 160-meter-long moonlet Dimorphos, which orbits the 760-meter-long asteroid Didymos. Neither of them poses a threat to Earth, and changing the orbit of the smaller asteroid around its larger companion was highly unlikely. The mission, known as the "Double Asteroid Redirection Test" (DART), was successful, demonstrating that it is possible to deflect an asteroid away from Earth.

However, painstaking telescopic observations of this pair now show that DART's suicidal collision with Dimorphos was so powerful that the rebounding moonlet created a gravitational shift for Didymos, moving both asteroids into a different orbit around the Sun.

In other words, "by hitting the moonlet with such force, we also slightly moved the giant object next to it," said Andy Rivkin, a planetary astronomer at the Johns Hopkins University Applied Physics Laboratory and one of the authors of a new study published on March 6 in Science Ad. This is the first time humanity has changed an asteroid's solar orbit.

Binary asteroids, such as Didymos and Dimorphos, share a common gravitational center. The larger object dominates the center of this region—in this case, Didymos, which is 200 times more massive than its moonlet. But if the smaller object is hit, its larger sibling will also "feel" it.

Before DART's collision with Dimorphos in 2022, scientists had to consider all possible outcomes of the mission, including several grim scenarios. "What if this experiment puts the Didymos system on a collision course with Earth?" said Rahil Makadia, another author of the study and a planetary defense researcher at the University of Illinois Urbana-Champaign. "That's obviously undesirable. So we studied that question."

They found that there would be no noticeable impact on Didymos. It would feel the impact on Dimorphos, but Didymos itself would not move.

Instead, NASA stated that for the mission to be considered successful, DART had to change Dimorphos's orbit around Didymos by 73 seconds. Instead, the small, van-sized spacecraft shortened the asteroid's orbit by 33 minutes—thanks to the force of DART's impact and the ejection of debris that broke off Dimorphos during the collision.

Before the mission, astronomers assumed that Dimorphos was a so-called rubble pile: instead of a giant solid rock, it was more like a cluster of boulders barely held together by the asteroid's weak gravity. If it were hit by a spacecraft at 14,000 miles per hour, part of it would inevitably break off into space.

But DART's impact ejected far more debris than anyone expected. This plume of material acted like a rocket jet, powerfully pushing the asteroid backward, much more strongly than many had predicted.

Everyone watching this drama thought the same thing: "This must have unexpected consequences," says Federica Spoto, an asteroid dynamics researcher at the Harvard-Smithsonian Center for Astrophysics, who was not involved in the new study. If Dimorphos was so heavily impacted by the spacecraft, what could have happened to Didymos?

After DART's failure in 2022, Makadia and his team tracked Didymos and Dimorphos using a method called stellar occultation. This is a complex process that requires being at the right telescope at the right time to observe a celestial object passing in front of a distant star. Based on how the object temporarily blocks starlight, astronomers can determine how fast and in what direction it is moving in space.

Through nearly two dozen stellar occultations, Makadia's team determined that the asteroid pair had slowed down—but only by 22 millionths of a mile per hour. For comparison, a typical garden snail moves about 1,000 times faster.

Unlike the change in Dimorphos's orbit around Didymos, the change in Didymos's heliocentric path was minuscule—"equivalent to moving the Didymos system the length of the Eiffel Tower in a year," says Cristina Thomas, a planetary astronomer at Northern Arizona University, who was not involved.

"It's a tiny, very tiny change," says Makadia. But over time, minor changes can accumulate and drastically alter asteroid orbits. Just in case, they performed calculations to understand where Didymos and its moonlet might end up in the long term.

"Don't worry," the publication writes. "We are safe from Didymos colliding with Earth," says Makadia.

Later this year, the European Space Agency's Hera spacecraft will arrive at Dimorphos to study the debris left by DART. This will undoubtedly reveal new details about humanity's first-ever planetary defense experiment. The spacecraft may have shattered into a million pieces in 2022, but it left behind a wealth of interesting scientific data that could help protect Earth if (or when) humanity discovers an approaching space rock.

Astronomers discover second-fastest asteroid in the Solar System25.10.25, 13:49 • 6086 views