The James Webb Space Telescope and the Hubble Space Telescope, two of NASA‘s Great Observatories, have captured images 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 observations of NASA’s Double Asteroid Redirection Test (DART) impact are the first time Webb and Hubble have observed the same celestial target at the same time.
DART intentionally smashed Dimorphos, the asteroid moonlet in Didymos’ double-asteroid system, on September 26, 2022, at 7:14 p.m. EDT. It was the world’s first test of the kinetic impact mitigation technique, which is associated with using a spacecraft to deflect and alter the orbit of an asteroid that poses no threat to Earth. DART is a test for defending Earth from asteroid or comet threats.
The coordinated Hubble and Webb observations are more than just an operational milestone for each telescope; they also allow researchers to investigate key science questions about the structure and history of our solar system by combining the capabilities of these observatories.
“Webb and Hubble show what we’ve always known to be true at NASA: We learn more when we work together,” said NASA Administrator Bill Nelson.
He continued: “For the first time, Webb and Hubble have simultaneously captured imagery from the same target in the cosmos: an asteroid that was impacted by a spacecraft after a seven-million-mile journey. All of humanity eagerly awaits the discoveries to come from Webb, Hubble, and our ground-based telescopes – about the DART mission and beyond.”
The observations from Webb and Hubble will allow scientists to learn more about the nature of Dimorphos’ surface, how much material was ejected by the collision, and how fast it was ejected. Besides that, Webb and Hubble captured the impact in different light wavelengths – Webb in infrared and Hubble in visible. Observing the impact at various wavelengths will reveal the distribution of particle sizes in the expanding dust cloud, assisting in determining whether it emitted a lot of large chunks or mostly fine dust.
Combining this data with observations from ground-based telescopes will allow scientists to better understand how effectively a kinetic impact can alter an asteroid’s orbit.
Webb Captures Impact Site Before and After Collision
Webb made one observation of the impact site before the collision, then several more over the next few hours. Webb‘s Near-Infrared Camera (NIRCam) images show a tight, compact core, with plumes of material appearing as wisps streaming away from the impact site.
Because of the asteroid’s speed across the sky, observing the impact with Webb presented unique challenges to the flight operations, planning, and science teams. As DART approached its target, the teams worked hard in the weeks before the impact to enable and test a method of tracking asteroids that were moving three times faster than the original speed limit set for Webb.
“I have nothing but tremendous admiration for the Webb Mission Operations folks that made this a reality,” said principal investigator Cristina Thomas of Northern Arizona University in Flagstaff, Arizona. “We have been planning these observations for years, then in detail for weeks, and I’m tremendously happy this has come to fruition.”
In the coming months, scientists plan to observe the asteroid system with Webb‘s Mid-Infrared Instrument (MIRI) and Webb‘s Near-Infrared Spectrograph (NIRS) (NIRSpec). Spectroscopic data will provide researchers with information about the chemical composition of the asteroid.
Webb observed the impact for five hours and took ten photos. Webb‘s Cycle 1 Guaranteed Time Observation Program 1245, led by Heidi Hammel of the Association of Universities for Research in Astronomy, collected the data (AURA).
Hubble Images Show Movement of Ejecta After Impact
Hubble also took photos of the binary system before the impact, as well as 15 minutes after DART landed on Dimorphos’ surface. In visible light, images from Hubble‘s Wide Field Camera 3 show the impact. Ejecta from the impact appears as rays stretching out from the asteroid’s body. The bolder, fanned-out ejecta spike to the left of the asteroid is in the general direction of DART‘s approach.
Some of the rays appear to be slightly curved, but astronomers must investigate further to determine what this could mean. Astronomers estimate that the brightness of the system increased three times after impact and that brightness remained constant even eight hours later.
Hubble plans to observe the Didymos-Dimorphos system ten more times in the next three weeks. These relatively long-term observations of the ejecta cloud as it expands and fades over time will provide a more complete picture of the cloud’s expansion from ejection to disappearance.
“When I saw the data, I was literally speechless, stunned by the amazing detail of the ejecta that Hubble captured,” said Jian-Yang Li of the Planetary Science Institute in Tucson, Arizona, who led the Hubble observations. “I feel lucky to witness this moment and be part of the team that made this happen.”
Hubble took 45 photos of the times before and after DART collided with Dimorphos. Cycle 29 General Observers Program 16674 collected the Hubble data.
“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.