Scientists Confirm DART Mission Permanently Altered Asteroid's Shape and Orbit

Historic Planetary Defense Success

When NASA's DART spacecraft slammed into the asteroid Dimorphos in September 2022, it achieved something unprecedented in human history: humanity's first time purposely changing the motion of a celestial object and the first full-scale demonstration of asteroid deflection technology . The 1,260-pound spacecraft, traveling at 14,000 miles per hour, struck the football stadium-sized asteroid moon with devastating precision.

Prior to DART's impact, Dimorphos orbited its larger parent asteroid, Didymos, once every 11 hours and 55 minutes, and DART's hypervelocity impact shortened this time to 11 hours and 23 minutes – a difference of 32 minutes . This exceeded NASA's most optimistic predictions by more than triple, as NASA initially predicted the orbit would be shortened by somewhere around 10 minutes .

The mission's success stems from more than just the spacecraft's direct impact. This deflection is the result of DART's kinetic impact and the "ejecta" – the many tons of asteroidal rock displaced and launched into space by the impact. The recoil from this blast of debris substantially enhanced DART's push against Dimorphos – a little like a jet of air streaming out of a balloon sends the balloon in the opposite direction .

Unexpected Consequences and New Discoveries

Recent research published in 2024 reveals that DART's impact created far more dramatic changes than initially understood. When NASA's Double Asteroid Redirection Test (DART) spacecraft collided with an asteroid moon called Dimorphos in 2022, the moon was significantly deformed—creating a large crater and reshaping it so dramatically that the moon derailed from its original evolutionary progression .

The impact unleashed an unexpected side effect: The test succeeded in knocking Dimorphos slightly off course but also dislodged from its surface 37 boulders that are now moving away from the asteroid. According to images taken by NASA's Hubble Space Telescope, the collision also shook off 37 boulders, each measuring from 3 to 22 feet across . While these boulders pose no threat to Earth, they highlight potential complications for future asteroid deflection missions.

Scientists have discovered that Dimorphos may start to "tumble" chaotically in its attempts to move back into gravitational equilibrium with its parent asteroid named Didymos . Originally, Dimorphos was probably in a very relaxed state and had one side pointing toward the main body, Didymos, just like how Earth's moon always has one face pointing toward our planet. Now, it's knocked out of alignment, which means it may wobble back and forth in its orientation. Dimorphos might also be 'tumbling,' meaning that we may have caused it to rotate chaotically and unpredictably .

Understanding Asteroid Composition

DART's close-up observations revealed crucial details about asteroid structure and formation. Images taken by DART showed Dimorphos to be a mixed collection of rocks from centimeters to tens of meters in size, jumbled together but making a remarkably smooth overall shape compared to other asteroids visited by spacecraft . This confirms that Dimorphos is what scientists call a "rubble pile" asteroid.

Analysis suggests significant age differences between the two asteroids. The team estimates that Didymos has a surface that is 40 to 130 times older than Dimorphos, with Didymos' surface being around 12.5 million years old and Dimorphos' surface being less than 300,000 years old. With Dimorphos' surface being so young, it is not nearly as strong as Didymos' surface, which is why DART's impact likely impacted the moonlet's orbit so significantly .

The research also revealed that Didymos' bearing capacity — the surface's ability to support applied loads — to be at least 1,000 times lower than that of dry sand on Earth or lunar soil . This weakness in surface strength contributed to DART's dramatic success in altering the asteroid's trajectory.

Looking Ahead: Future Planetary Defense

The European Space Agency's Hera mission, poised for launch in October 2024, will revisit the Didymos asteroid system to study the aftermath of DART's kinetic impactor experiment and further enhance future asteroid deflection missions and science . By late 2026, Hera will arrive at the binary asteroid system containing Dimorphos and Didymos to assess the internal properties of both asteroids for the first time, providing a more detailed analysis of the DART mission and its implications for the future .

DART's success validates kinetic impact as a viable planetary defense strategy, but questions remain about its effectiveness against different types of asteroids. More research is still needed to fully understand if a kinetic impactor spacecraft would be as effective in mitigating against a more solid object than rubble-pile Dimorphos that would eject less material into space upon collision by a spacecraft .

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