Webb, Hubble Capture Detailed Views of DART Impact

Two of NASA’s Great Observatories, the James Webb Space Telescope and the Hubble Space Telescope, have captured views of a unique NASA experiment designed to intentionally smash a spacecraft into a small asteroid in the world’s first-ever in-space test for planetary defense.

These images from NASA’s Hubble Space Telescope, taken (left to right) 22 minutes, 5 hours, and 8.2 hours after NASA’s Double Asteroid Redirection Test (DART) intentionally impacted Dimorphos, show expanding plumes of ejecta from the asteroid’s body. The Hubble images show ejecta from the impact that appear as rays stretching out from the body of the asteroid. The bolder, fanned-out spike of ejecta to the left of the asteroid is in the general direction from which DART approached. Photo: Science: NASA, ESA, Jian-Yang Li (PSI); image processing: Alyssa Pagan (STScI)

On Sept. 26, 2022, at 7:14 pm EDT, DART intentionally crashed into Dimorphos, the asteroid moonlet in the double-asteroid system of Didymos.

It was the world’s first test of the kinetic impact mitigation technique, using a spacecraft to deflect an asteroid that poses no threat to Earth, and modifying the object’s orbit. DART is a test for defending Earth against potential asteroid or comet hazards.

The coordinated Hubble and Webb observations are more than just an operational milestone for each telescope – there are also key science questions relating to the makeup and history of our solar system that researchers can explore when combining the capabilities of these observatories.

Observations from Webb and Hubble together will allow scientists to gain knowledge about the nature of the surface of Dimorphos, how much material was ejected by the collision, and how fast it was ejected.

Additionally, Webb and Hubble captured the impact in different wavelengths of light – Webb in infrared and Hubble in visible.

Observing the impact across a wide array of wavelengths will reveal the distribution of particle sizes in the expanding dust cloud, helping to determine whether it threw off lots of big chunks or mostly fine dust.

Combining this information, along with ground-based telescope observations, will help scientists to understand how effectively a kinetic impact can modify an asteroid’s orbit.

Webb took one observation of the impact location before the collision took place, then several observations over the next few hours. Images from Webb’s Near-Infrared Camera (NIRCam) show a tight, compact core, with plumes of material appearing as wisps streaming away from the center of where the impact took place.

Observing the impact with Webb presented the flight operations, planning, and science teams with unique challenges, because of the asteroid’s speed of travel across the sky.

As DART approached its target, the teams performed additional work in the weeks leading up to the impact to enable and test a method of tracking asteroids moving over three times faster than the original speed limit set for Webb.

Scientists also plan to observe the asteroid system in the coming months using Webb’s Mid-Infrared Instrument (MIRI) and Webb’s Near-Infrared Spectrograph (NIRSpec). Spectroscopic data will provide researchers with insight into the asteroid’s chemical composition.

Hubble also captured observations of the binary system ahead of the impact, then again 15 minutes after DART hit the surface of Dimorphos. Images from Hubble’s Wide Field Camera 3 show the impact in visible light.

Ejecta from the impact appear as rays stretching out from the body of the asteroid.

The bolder, fanned-out spike of ejecta to the left of the asteroid is in the general direction from which DART approached.

Some of the rays appear to be curved slightly, but astronomers need to take a closer look to determine what this could mean. In the Hubble images, astronomers estimate that the brightness of the system increased by three times after impact, and saw that brightness hold steady, even eight hours after impact.

Hubble plans to monitor the Didymos-Dimorphos system 10 more times over the next three weeks.

These regular, relatively long-term observations as the ejecta cloud expands and fades over time will paint a more complete picture of the cloud’s expansion from the ejection to its disappearance.

“This is an unprecedented view of an unprecedented event,” summarized Andy Rivkin, DART investigation team lead of the Johns Hopkins University Applied Physics Laboratory in Laurel, Maryland. (NASA)

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