Are boulders falling out of asteroid Dimorphos?

The asteroid Dimorphos has been captured in this image, with accompanying compass arrows, a scale bar, and color key for reference.The north and east arrows give viewers an idea of the orientation of the image on the sky. It is important to note that the relationship between north and east as seen from below is flipped relative to the direction arrows on a map of the ground as seen from above.

The popular 1954 rock song “Shake, Rattle and Roll” perfectly captures the spirit of the news from the Hubble Space Telescope about the asteroid Dimorphos and its recent encounter with NASA’s Double Asteroid Redirection Test (DART). On September 26, 2022, DART intentionally impacted Dimorphos, slightly changing its orbit around the larger asteroid Didymos. The 37 free-floating boulders range in size from three feet to 22 feet across, and their combined mass is 0.1% of that of Dimorphos’s. But what’s really amazing is their slow speed: just over half a mile an hour, or about the walking speed of a giant tortoise. And yet, they are still carrying mass and energy away from the impact site. 

This discovery is nothing short of incredible. Planetary scientist David Jewitt of the University of California at Los Angeles, who has been using Hubble to study Dimorphos before and after the DART impact, said it best: “This tells us what happens when you hit an asteroid and see material coming out up to the largest sizes. The boulders are some of the faintest things ever imaged inside our solar system.” To think that something so small can have such a big impact is really incredible. It also speaks to our need as a species to continue exploring space. The more we discover about asteroids and other celestial bodies, the more we can learn about our own planet and our place in the universe.      

The knowledge we gain from this discovery could be invaluable in protecting us from any future asteroid threats. After all, if we can figure out how to deflect an asteroid with something as small as a half-ton spacecraft, imagine what other kinds of protection we might be able to develop in the future! It’s also worth noting that this discovery wouldn’t have been possible without Hubble’s extraordinary sensitivity and power. Now more than ever it’s clear that investing in space exploration is worth it – not only does it push humanity forward, but it also enables us to make life-changing discoveries like this one.

Jewitt’s remarks make it very clear that the European Space Agency’s upcoming Hera spacecraft mission to the binary asteroid in late 2026 will be a unique opportunity for scientists to study the aftermath of the DART experiment. Hera will perform a detailed survey of the asteroid, studying the boulder cloud which will still be dispersing when it arrives, akin to a slowly expanding swarm of bees spreading along the binary pair’s orbit around the Sun.This cloud is likely made up of rocks that were already scattered across the asteroid’s surface before impact,as seen in DART’s close-up picture taken just two seconds before collision at seven miles above the surface.With this opportunity to study the aftermath of the impact,scientists can gain valuable insight into the formation and evolution of asteroids and their potential as resources for space exploration.

NASA’s DART spacecraft successfully hits asteroid in planetary defense test.

On September 26, 2022, the NASA DART (Double Asteroid Redirection Test) impactor spacecraft successfully impacted its target, the asteroid Dimorphos. Captured by the Didymos Reconnaissance and Asteroid Camera for Optical navigation (DRACO) imager aboard the spacecraft, this is the last complete image of Dimorphos seen on Earth.

Astronomer David Jewitt of the University of California, Los Angeles, has estimated that the impact shook off two percent of the boulders on the asteroid’s surface. He further adds that the boulders observed by Hubble give an estimate for the size of the impact crater. According to Jewitt, the crater measured approximately 160 feet across which is roughly equal to the width of a football field. 

The impact event was captured by the LICIACube (Light Italian CubeSat for Imaging of Asteroids) and its LUKE (LICIACube Unit Key Explorer) camera. The boulder trajectories were tracked in the minutes following the impact and it was found that they had been launched in various directions. These observations have paved the way for further exploration into understanding how exactly these boulders were lifted off Dimorphos’ surface. 

It is speculated that Dimorphos was formed from material shed into space by its larger parent body, asteroid Didymos. This could have happened due to Didymos spinning up too quickly or from a collision with another object which caused some of its material to be ejected into space. This material then coalesced into Dimorphos and gave it its “flying rubble pile” structure, which means that it is not solid but rather made up of loosely held together debris held together by a weak gravitational pull. 

Though the data gathered from the LICIACube and Hubble allows us to make some educated guesses as to how Dimorphos came to be and what was the result of the DART mission, further exploration in this area is necessary to gain a more comprehensive understanding. The Hera mission has been launched to answer any outstanding questions regarding this collision and its long-term effects on Dimorphos and thus provide deeper insight into asteroids in general.