This Hubble Space Telescope image of the asteroid Dimorphos was taken on December 19, 2022, nearly four months after the asteroid was impacted by NASA’s Double Asteroid Redirection Test (DART) mission. Hubble’s sensitivity reveals a few dozen rocks torn from the asteroid by the force of the collision. They are among the faintest objects Hubble has ever photographed inside the solar system. The loose boulders range in size from three feet to 22 feet in diameter, based on Hubble photometry. They are moving away from the asteroid at just over half a mile per hour. The discovery gives invaluable information about the behavior of a small asteroid when hit by a projectile in an attempt to alter its trajectory. Credit: NASA, ESA, David Jewitt (UCLA), Alyssa Pagan (STScI)

The impact of the DART 2022 mission shook the surface of the asteroid

Sorry Chicken Little, the sky isn’t falling – at least not yet.

Wayward asteroids present a real danger of collision with Earth. Scientists estimate that an asteroid several miles in diameter crashed into Earth 65 million years ago and wiped out dinosaurs, among other life forms, in a mass extinction. Unlike the dinosaurs, humanity can avoid this fate if we start practicing deflecting an asteroid approaching Earth.

It’s trickier than how it’s been portrayed in sci-fi movies like Deep Impact. Planetary scientists must first know how the asteroids were assembled. Are they stealing piles of loosely clumped rock rubble, or something more substantial? This information would help provide strategies on how to successfully deflect a threatening asteroid.

To begin with, Nasa did an experiment to crash an asteroid to see how disturbed it is. The impact of the Double Asteroid Redirection Test (DART) spacecraft on the asteroid Dimorphos occurred on September 26, 2022. Astronomers using the The Hubble Space Telescope continue to follow the consequences of the cosmic collision. A surprise is the discovery of several dozen rocks lifted from the asteroid after the crash. In Hubble images, they look like a swarm of bees moving very slowly away from the asteroid. This could mean that hitting an asteroid approaching Earth could cause an ominous group of rocks to form heading in our direction.

Image of the asteroid Dimorphos, with compass arrows, scale bar and color key for reference.
The north and east arrows of the compass indicate the orientation of the image on the sky. Note that the relationship between north and east on the sky (viewed from below) is reversed compared to the direction arrows on a map on the ground (viewed from above).
The glowing white object in the lower left is Dimorphos. It has a bluish dust tail extending diagonally to the upper right. A group of blue dots (marked by white circles) surrounds the asteroid. These are rocks that were knocked off the asteroid when, on September 26, 2022, NASA deliberately threw the half-ton DART impactor spacecraft into the asteroid to test what it would take to prevent a future asteroid from hitting Earth. Hubble photographed the slow-moving rocks using Wide Field Camera 3 in December 2022. The color results from assigning a blue tint to the monochromatic (grayscale) image.
Credit: NASA, ESA, David Jewitt (UCLA), Alyssa Pagan (STScI)

The popular 1954 rock song “Shake, Rattle and Roll” may be the theme song to the Hubble Space Telescope’s latest discovery of what happens to the asteroid Dimorphos in the wake of NASA DART (Double Asteroid Redirection Test). DART intentionally impacted Dimorphos on September 26, 2022, change the trajectory slightly from its orbit around the larger asteroid Didymos.

Astronomers using Hubble’s extraordinary sensitivity have discovered a swarm of rocks that may have been rocked from the asteroid when NASA deliberately hurled the half-ton DART impactor spacecraft onto Dimorphos at around 14,000 miles per hour.

The 37 free rocks range in size from three feet to 22 feet in diameter, based on Hubble photometry. They are moving away from the asteroid at just over half a mile per hour, about the walking speed of a giant tortoise. The total mass of these rocks detected is about 0.1% of the mass of Dimorphos.

This is the last full image of the asteroid Dimorphos, seen by NASA’s Double Asteroid Redirection Test (DART) impacting spacecraft two seconds before impact. The DRACO (Didymos Reconnaissance and Asteroid Camera for Optical navigation) imager on board captured a 100-foot-wide area of ​​the asteroid. The DART spacecraft broadcast these images from its DRACO camera to Earth in real time as it approached the asteroid. DART successfully hit its target on September 26, 2022. Credit: NASA, APL

“This is a spectacular sighting – much better than I expected. We see a cloud of boulders carrying mass and energy away from the impact target. The number, size and shape of the boulders are consistent with the fact that they were knocked off the surface of Dimorphos by the impact,” said David Jewitt of the University of California, Los Angeles, a planetary scientist who used Hubble to track changes in the asteroid during and after the impact. DART impact.” This tells us for the first time what happens when you hit an asteroid and see material coming out up to the largest sizes. Rocks are some of the faintest things ever photographed inside our solar system.

Jewitt says this opens a new dimension for studying the consequences of the DART experiment using the European Space AgencyIt is next Hera spacecraft, which will arrive at the binary asteroid in late 2026. Hera will perform a detailed post-impact survey of the targeted asteroid. “The boulder cloud will still be dispersing when Hera arrives,” Jewitt said. “It’s like a very slowly expanding swarm of bees that will eventually spread along the binary pair’s orbit around the Sun.”

This illustration depicts NASA’s Double Asteroid Redirection Test (DART) spacecraft prior to impact on the binary asteroid system Didymos. Credit: NASA/Johns Hopkins APL/Steve Gribben

The rocks are probably not broken pieces of the small asteroid caused by the impact. They were already scattered across the asteroid’s surface, as evidenced by the last close-up photo taken by the DART spacecraft just two seconds before the collision, when it was just seven miles above the surface.

Jewitt estimates that the impact jolted two percent of the rocks on the asteroid’s surface. He says Hubble’s rock observations also give an estimate of the size of the DART impact crater. “The boulders could have been extracted from a circle about 160 feet in diameter (the width of a football field) on the surface of Dimorphos,” he said. Hera will eventually figure out the actual size of the crater.

Long ago, Dimorphos may have formed from material thrown into space by the larger asteroid Didymos. The parent body may have rotated too quickly or may have lost material due to collision with another object, among other scenarios. The ejected material formed a ring which coalesced under gravity to form Dimorphos. This would make it a flying rubble pile of rocky debris held together by a relatively weak force of gravity. Therefore, the inside is probably not solid, but has a structure that looks more like a bunch of grapes.

It is not known how the rocks were lifted from the surface of the asteroid. They could be part of an ejecta plume photographed by Hubble and other observatories. Or a seismic wave from the impact may have rocked the asteroid – like hitting a bell with a hammer – shaking rubble from the surface.

“If we track the boulders in future Hubble observations, we might have enough data to determine the precise trajectories of the boulders. And then we’ll see what directions they were thrown from the surface,” Jewitt said.

The DART and LICIACube (Light Italian CubeSat for Imaging of Asteroids) teams also studied rocks detected in images taken by LICIACube’s LUKE (LICIACube Unit Key Explorer) camera in the minutes immediately following the kinetic impact of DART.

The Hubble Space Telescope is an international cooperation project between NASA and ESA. NASA’s Goddard Space Flight Center in Greenbelt, Maryland operates the telescope. The Space Telescope Science Institute (STScI) in Baltimore, Maryland conducts Hubble and Webb science operations. STScI is operated for NASA by the Association of Universities for Research in Astronomy, in Washington, D.C.