December 7, 2023


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Hubble sees rocks escaping from the asteroid Dimorphos

Hubble sees rocks escaping from the asteroid Dimorphos

This Hubble Space Telescope image of the asteroid Dimorphos was taken on December 19, 2022, roughly four months after the asteroid impact, by NASA’s DART (Double Asteroid Redirection Test) mission. Hubble’s sensitivity reveals a few dozen rocks that were shattered from the asteroid by the force of the impact. These are among the faintest objects ever imaged by Hubble within the Solar System. The free falling rocks range in size from three feet to 22 feet wide, based on the Hubble Photometry. They are moving away from the asteroid at just over half a mile per hour. This discovery provides invaluable insights into the behavior of a small asteroid when it is hit by a projectile intended to change its trajectory. Credit: NASA, ESA, David Jewett (UCLA) and Alyssa Pagan (STScI)

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

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

Asteroid strikes pose a real risk of colliding with Earth. Scientists estimate that an asteroid several miles across smashed into Earth 65 million years ago and wiped out the dinosaurs, among other forms of life, in a mass extinction. Unlike the dinosaurs, humanity can avoid this fate if we start practicing how to derail an asteroid approaching Earth.

This is more difficult than depicted in sci-fi movies like Deep Impact. Planetary scientists first need to figure out how to group asteroids. Are heaps of loosely agglomerated rock flying, or something more significant? This information will help provide strategies on how to successfully deflect the threatening asteroid.

as a first step, NASA He conducted an experiment to smash an asteroid to see how upset it was. The DART (Double Asteroid Redirection Test) spacecraft impact occurred on the asteroid Dimorphos on September 26, 2022. Astronomers used Hubble Space Telescope Continue to follow the effects of the cosmic collision. The surprise is the discovery of several dozen rocks that were lifted from the asteroid after the collapse. In the Hubble images, they appear to be a swarm of bees moving very slowly away from the asteroid. This could mean that hitting an asteroid approaching Earth could send a menacing group of rocks heading in our direction.

Hubble images of rocks falling from the asteroid Dimorphos

Image of the asteroid Dimorphos, with compass and tape measure arrows and a color key for reference.
The north and east compass arrow shows the image’s direction in the sky. Note that the relationship between north and east in the sky (as seen from below) is inverted relative to the directional arrows on the Earth map (as seen from above).
The bright white object on the lower left is Dimorphos. It has a bluish dust tail that extends diagonally to the upper right. A group of blue dots (marked with white circles) surrounds the asteroid. These are the rocks that were shattered from the asteroid when, on September 26, 2022, NASA deliberately rammed the half-ton DART spacecraft into the asteroid as a test of what it might take to deflect some future asteroids from crashing into Earth. Hubble imaged slow-motion rocks with the Wide Field Camera 3 in December 2022. The color results from the assignment of a blue hue to the monochrome (grayscale) image.
Credit: NASA, ESA, David Jewett (UCLA) and Alyssa Pagan (STScI)

The iconic 1954 rock song “Shake, Rattle and Roll” could have been the theme music for recent Hubble Space Telescope discoveries about what happens to the asteroid Dimorphos in the aftermath of NASA’s DART (Double Asteroid Redirection Test) experiment. DART intentionally impacted Dimorphos on September 26, 2022, slightly changing the trajectory of its orbit around the larger asteroid Didymos.

Astronomers using Hubble’s extraordinary sensitivity detected a swarm of rocks that likely shook from the asteroid when NASA deliberately rammed the half-ton DART spacecraft into Dimorphos at nearly 14,000 miles per hour.

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

Surface image of the asteroid Dimorphos

This is the last complete image of the asteroid Dimorphos, as seen by NASA’s DART (Double Asteroid Reorientation Test) spacecraft two seconds before impact. The Didymus Reconnaissance Camera and the Asteroid Optical Navigation Camera (DRACO) onboard captured a 100-foot-wide spot of the asteroid. The DART spacecraft broadcast these images from the DRACO camera back to Earth in real time as it approached the asteroid. DART successfully impacted its target on Sept. 26, 2022. Credit: NASA, APL

“This is a fascinating observation—much better than I expected. We see a cloud of rocks carrying mass and energy away from the impact target. The numbers, sizes, and shapes of the rocks are consistent with falling off the surface of Dimorphos due to the impact,” said David Jewett of UCLA, a planetary scientist who has been using Hubble to track changes in the asteroid during and after the Dart impact. “This tells us for the first time what happens when you hit an asteroid and see material come out in larger sizes. Rocks are some of the weakest objects ever photographed within our solar system. “

Jewett says this opens up a new dimension for studying the effects of the DART experiment European Space AgencyThe upcoming HERA spacecraft, which will reach the binary asteroid in late 2026. HERA will perform a detailed post-impact survey of the target asteroid. “The cloud of rock will still disperse when Hera arrives,” Jewett said. “It’s like a very slowly expanding swarm of bees that will eventually scatter along the binary pair’s orbit around the Sun.”

NASA orbited the spacecraft before impact

This illustration depicts a NASA spacecraft for the Double Asteroid Redirection Test (DART) prior to collision in the Didymos binary asteroid system. Image credit: NASA/Johns Hopkins APL/Steve Gribben

It is likely that the rocks were not splintered from the small asteroid that the impact caused. They were already scattered across the asteroid’s surface, as can be seen in the last close-up image taken by the DART spacecraft just two seconds before impact, when it was just seven miles above the surface.

Jewett estimates that the impact shook 2% of the rocks on the asteroid’s surface. He says the rock observations made by Hubble also give an estimate of the size of the DART impact crater. “It would have been possible to excavate the rock from a circle about 160 feet wide (the width of a football field) on the surface of Dimorphos,” he said. Hera would eventually determine the actual hole size.

A long time ago, Dimorphos may have formed from matter hurled into space by the larger asteroid Didymus. The parent body may have spun too quickly or it may have lost material from a light collision with another body, among other scenarios. The ejected material formed a ring that gravitationally fused to form a dimorphose. This would make it a flying rubble pile of rocky debris held loosely by the relatively weak pull of gravity. Therefore, the inner part is probably not solid, but has a structure much like a bunch of grapes.

It is not clear how the rocks were lifted from the asteroid’s surface. It could be part of an ejection plume imaged by Hubble and other observatories. Or the seismic wave from the impact could have vibrated through the asteroid – like hitting a bell with a hammer – causing the surface debris to lose vibration.

“If we follow the rocks in future Hubble observations, we may have enough data to pinpoint the tracks of the rocks. And then we’ll see in which directions they were launched from the surface,” Jewett said.

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

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

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