Hubble discovers swarm of boulders after asteroid impact

Astronomers have made a remarkable discovery through the Hubble Space Telescope concerning the aftermath of NASA’s DART (Double Asteroid Redirection Test) experiment, which took place on September 26, 2022. The purpose of this experiment was to study how an asteroid reacts when impacted by a spacecraft.

One surprising finding is the existence of several dozen boulders that were dislodged from the asteroid after the collision. These boulders appear to be slowly drifting away from the asteroid in a manner reminiscent of a swarm of bees. This unexpected revelation raises concerns that a similar impact on an Earth-approaching asteroid could result in a cluster of dangerous boulders heading towards our planet.

The Hubble Space Telescope’s extraordinary sensitivity allowed astronomers to observe these free-floating boulders, ranging in size from three to twenty-two feet across. The boulders are moving away from the asteroid at a slow pace, slightly more than half a mile per hour—about the walking speed of a giant tortoise. The total mass of these detected boulders constitutes just about 0.1% of the mass of Dimorphos, the asteroid impacted by the DART spacecraft.

Understanding how asteroids are assembled is a crucial step in devising effective strategies to deflect potential Earth-approaching asteroids and safeguarding our planet from potential hazards. By gathering more data and insights from experiments like DART and observations from the Hubble Space Telescope, scientists can enhance their knowledge and develop better plans to protect Earth from the risks posed by wayward asteroids.

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

The recent observations made through the Hubble Space Telescope have been nothing short of extraordinary, exceeding all expectations. According to David Jewitt, a planetary scientist from the University of California at Los Angeles, the data reveals an impressive cloud of boulders carrying both mass and energy away from the impact target on asteroid Dimorphos. This remarkable event occurred during the DART (Double Asteroid Redirection Test) experiment, where the spacecraft intentionally collided with the asteroid.

Jewitt emphasizes the significance of this discovery, as it provides crucial insights into the aftermath of an asteroid impact, capturing material being ejected from the asteroid surface, even up to the largest boulders. These boulders, which are among the faintest objects ever imaged within our solar system, offer valuable data for further analysis.

Looking ahead, Jewitt sees immense potential in the upcoming Hera spacecraft mission by the European Space Agency, set to arrive at the binary asteroid in late 2026. Hera’s detailed post-impact survey will continue to study the boulder cloud, which is slowly dispersing, resembling an expanding swarm of bees following the orbit around the sun.

Interestingly, the boulders appear to have been scattered across Dimorphos’ surface even before the impact. The collision likely shook off about two percent of the boulders present on the asteroid’s surface, and Hubble’s observations also provide an estimate of the size of the DART impact crater.

Dimorphos itself may have formed from material ejected into space by the larger asteroid Didymos, possibly due to rapid spinning or glancing collisions with other objects. As a result, Dimorphos is likely a conglomerate of loosely held rocky debris, held together by a relatively weak gravitational force, resembling a cluster of grapes rather than a solid structure.

The exact mechanism that lifted the boulders off the asteroid’s surface remains unclear. It could be linked to an ejecta plume captured in Hubble’s photographs or a seismic wave caused by the impact, causing surface rubble to shake loose.

Continued observations by Hubble may help determine the precise trajectories of the boulders and shed light on the directions from which they were launched off the surface.

These groundbreaking findings have been published in The Astrophysical Journal Letters, and they offer a fascinating glimpse into the dynamics of asteroid impacts and their potential implications for our understanding of celestial bodies.

Source: ESA/Hubble Information Centre

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