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Hubble sees boulders escaping from asteroid Dimorphos

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Hubble boulders Dimorphos The bright white object at lower left is the asteroid Dimorphos. It has a blue dust tail extending diagonally to the upper right. A cluster of blue dots surrounds the asteroid. These are boulders that were knocked off the asteroid when, on 26 September 2022, NASA deliberately slammed the half-tonne 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 in December 2022

Hubble sees boulders escaping from asteroid Dimorphos

Astronomers using the NASA/ESA/ Hubble Space Telescope’s extraordinary sensitivity have discovered a swarm of boulders that were possibly shaken off the asteroid Dimorphos when NASA deliberately slammed the half-tonne DART impactor spacecraft into Dimorphos at approximately 22 500 kilometres per hour. DART intentionally impacted Dimorphos on 26 September 2022, slightly changing the trajectory of its orbit around the larger asteroid Didymos.

Hubble boulders Dimorphos The bright white object at lower left is the asteroid Dimorphos. It has a blue dust tail extending diagonally to the upper right. A cluster of blue dots surrounds the asteroid. These are boulders that were knocked off the asteroid when, on 26 September 2022, NASA deliberately slammed the half-tonne 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 in December 2022
This NASA/ESA Hubble Space Telescope image of the asteroid Dimorphos was taken on 19 December 2022, nearly four months after the asteroid was impacted by NASA’s DART (Double Asteroid Redirection Test) mission. Hubble’s sensitivity reveals a few dozen boulders knocked off the asteroid by the force of the collision. These are among the faintest objects Hubble has ever photographed inside the Solar System. The ejected boulders range in size from 1 metre to 6.7 metres across, based on Hubble photometry. They are drifting away from the asteroid at around a kilometre per hour. The discovery yields invaluable insights into the behaviour of a small asteroid when it is hit by a projectile for the purpose of altering its trajectory.
Credit: NASA, ESA, D. Jewitt (UCLA)

The 37 ejected boulders range in size from 1 metre to 6.7 metres across, based on Hubble photometry. They are drifting away from the asteroid at around one kilometre per hour. The total mass in these detected boulders is about 0.1% the mass of Dimorphos. The boulders are some of the faintest objects ever imaged in the Solar System.

This opens up a new dimension for studying the aftermath of the DART experiment using the European Space Agency’s upcoming Hera mission, which is due to launch in 2024. The spacecraft will perform a detailed post-impact survey of the target asteroid Dimorphos. Hera will turn the grand-scale experiment into a well-understood and repeatable planetary defence technique that might one day be used for real [1].

The boulders are most likely not shattered pieces of the diminutive asteroid caused by the impact. They were already scattered across the asteroid’s surface, as evident in the last close-up picture taken by the DART spacecraft just two seconds before collision, when it was only 11 kilometres above the surface.

The science team that observed these boulders with Hubble estimates that the impact shook off two percent of the boulders on the asteroid’s surface. While the boulder observations by Hubble also give an estimate for the size of the DART impact crater, Hera will eventually determine the actual crater size.

Long ago, Dimorphos may have formed from material shed into space by the larger asteroid Didymos. The parent body may have spun up too quickly or could have lost material after a glancing collision with another object, among other scenarios. The ejected material formed a ring that gravitationally coalesced to form Dimorphos. This would make it a flying rubble pile of rocky debris loosely held together by the relatively weak pull of its gravity. Therefore, the interior is probably not solid, but has a structure more like a bunch of grapes.

It’s not clear how the boulders were lifted off the asteroid’s surface. They could be part of an ejecta plume that was photographed by Hubble and other observatories. Or a seismic wave from the impact may have rattled through the asteroid — like hitting a bell with a hammer — shaking loose the surface rubble.

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

Notes

[1] Just like Hubble and the NASA/ESA/CSA James Webb Space Telescope, NASA’s DART and ESA’s Hera missions are great examples of what international collaboration can achieve; the two missions are supported by the same teams of scientists and astronomers, and operate via an international collaboration called AIDA — the Asteroid Impact and Deflection Assessment.

NASA and ESA worked together in the early 2000s to develop asteroid monitoring systems, but recognised there was a missing link in the chain between asteroid threat identification and ways of addressing that threat. In response NASA oversaw the DART mission while ESA developed the Hera mission to gather additional data on DART’s impact. With the Hera mission, ESA is assuming even greater responsibility for protecting our planet and ensuring that Europe plays a leading role in the common effort to tackle asteroid risks. As Europe’s flagship planetary defender, Hera is supported through the Agency’s Space Safety programme, part of the Operations Directorate.

The bright white object at lower left is the asteroid Dimorphos. It has a blue dust tail extending diagonally to the upper right. A cluster of blue dots surrounds the asteroid. These are boulders that were knocked off the asteroid when, on 26 September 2022, NASA deliberately slammed the half-tonne 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 in December 2022
Hubble sees boulders escaping from asteroid Dimorphos: this NASA/ESA Hubble Space Telescope image of the asteroid Dimorphos was taken on 19 December 2022, nearly four months after the asteroid was impacted by NASA’s DART (Double Asteroid Redirection Test) mission. Hubble’s sensitivity reveals a few dozen boulders knocked off the asteroid by the force of the collision. These are among the faintest objects Hubble has ever photographed inside the Solar System. The ejected boulders range in size from 1 metre to 6.7 metres across, based on Hubble photometry. They are drifting away from the asteroid at around a kilometre per hour. The discovery yields invaluable insights into the behaviour of a small asteroid when it is hit by a projectile for the purpose of altering its trajectory.
Credit: NASA, ESA, D. Jewitt (UCLA)

Press release from ESA Hubble

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Astronomy

Hubble captures movie of DART asteroid impact debris

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Hubble captures DART asteroid impact debris

Hubble captures movie of DART asteroid impact debris

The NASA/ESA Hubble Space Telescope captured a series of photos of rapid changes to the asteroid Dimorphos when it was deliberately hit by a 545-kilogram spacecraft on 26 September 2022. The primary objective of the NASA mission, called DART (Double Asteroid Redirection Test), was to test our ability to alter the asteroid’s trajectory as it orbits its larger companion asteroid, Didymos. Though Dimorphos poses no threat to Earth, data from the mission could help inform researchers how to potentially change an asteroid’s path away from Earth, if ever necessary.

Hubble’s resulting time-lapse movie of the aftermath of the collision reveals surprising and remarkable changes as dust and chunks of debris were flung into space from the wounded asteroid. Smashing head-on into the asteroid at 21 000 kilometres per hour, the DART impactor blasted over 900 000 kilograms of dust off of the asteroid.

The Hubble movie provides invaluable new clues into how the debris was dispersed into a complex pattern in the days following the impact.

The movie shows three overlapping stages of the aftermath of the crash: the formation of an ejecta cone, the spiral swirl of debris caught up along the asteroid’s orbit about its companion asteroid, and the tail swept behind the asteroid by the pressure of sunlight.

The Hubble movie starts at 1.3 hours before impact. In this view both Didymos and Dimorphos are within the central bright spot; even Hubble can’t resolve the two asteroids separately. The thin, straight spikes projecting away from the centre (and seen in later images) are artefacts of Hubble’s optics. The first post-impact snapshot is two hours after the event. Debris flies away from the asteroid, moving in with a range of speeds faster than four miles per hour (fast enough to escape the asteroid’s gravitational pull, so it does not fall back onto the asteroid). The ejecta forms a largely hollow cone with long, stringy filaments.

At about 17 hours after the collision the debris pattern entered a second stage. The dynamic interaction within the binary system started to distort the cone shape of the ejecta pattern. The most prominent structures are rotating, pinwheel-shaped features. The pinwheel is tied to the gravitational pull of the companion asteroid, Didymos.

Hubble next captures the debris being swept back into a comet-like tail by the pressure of sunlight on the tiny dust particles. This stretches out into a debris train where the lightest particles travel the fastest and farthest from the asteroid. Hubble also recorded the tail splitting in two for a few days.

Due to launch in October 2024, ESA’s Hera mission will perform a detailed post-impact survey of the target asteroid Dimorphos. Hera will turn the grand-scale experiment into a well-understood and repeatable planetary defence technique that might one day be used for real.

Just like Hubble and the NASA/ESA/CSA James Webb Space Telescope, NASA’s DART and ESA’s Hera missions are great examples of what international collaboration can achieve; the two missions are supported by the same teams of scientists and astronomers, and operate via an international collaboration called AIDA — the Asteroid Impact and Deflection Assessment.

NASA and ESA worked together in the early 2000s to develop asteroid monitoring systems, but recognised there was a missing link in the chain between asteroid threat identification and ways of addressing that threat. In response NASA oversaw the DART mission while ESA developed the Hera mission to gather additional data on DART’s impact. With the Hera mission, ESA is assuming even greater responsibility for protecting our planet and ensuring that Europe plays a leading role in the common effort to tackle asteroid risks. As Europe’s flagship planetary defender, Hera is supported through the Agency’s Space Safety programme, part of the Operations Directorate.

 

Press release from ESA Hubble

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