when NASA The Double Asteroid Redirection Test (DART) spacecraft crashed into the small moon of asteroid Dimorphos on September 26, all eyes were on the crash.
Both the Hubble Space Telescope and the James Webb Space Telescope captured images of the DART impact, and will continue to monitor its aftermath for weeks and months to come. It is the first time that the two space telescopes have worked together in this way; Webb has already taken images of some of Hubble’s previous targets, but they never observed the same object at the same time.
Both telescopes took before-and-after snapshots of Dimorphos and Didymos, the largest asteroid it orbits. Because Webb and Hubble view the universe in different wavelengths of light, they can join forces to give scientists a much more complete view of the debris cloud that the DART impact generated, from the long infrared wavelengths medium to the shorter wavelengths of ultraviolet light.
The DART team will use that information to help them understand how hard DART hit Dimorphos and what effect the collision had on the little moon. To do that, they need to know things like how much material was thrown out of the impact site, how fast that debris is moving, and whether it’s mostly big chunks or small grains.
To accomplish this, Webb’s team had to figure out how to keep their eyes focused on a nearby object, which was moving through the telescope’s field of view about three times faster than anything Webb could track. Webb was built to study the faintest and most distant objects in the universe, but scientists still want to point it at nearby objects, too, and the telescope and its operators remain up to the challenge. It took several weeks to plan and test a tracking method for DART, but Webb’s team pulled it off, capturing 10 images in about five hours of observation.
Meanwhile, Hubble observed Dimorphos and Didymos for about an hour with its Wide Field Camera 3 (WFC 3). and in the process, he revealed some interesting puzzles for the DART science team to solve. A big question is why Didymos appeared to glow in the Hubble images for about eight hours after impact; Astronomers weren’t surprised that the little moon got brighter when DART hit it, but they are intrigued by how long the glow stayed, according to the European Space Agency (ESA).
The bright, spiky beams in the images are plumes of debris, ripped from Dimorphos’ surface by the impact. Some of them seem to curve slightly, and figuring out why will require a lot more analysis.
Webb and Hubble will also have a role to play in that process. Over the next three weeks, Hubble will monitor Didymos ten more times to record how the ejected debris cloud expands and fades. And Webb will communicate with its near-infrared spectrometer (NIRSpec) and mid-infrared instrument (MIRI) for several more months to help astronomers learn more about the small moon’s chemical composition.