(CN) — NASA released images Thursday, captured by the James Webb and Hubble space telescopes, of its DART probe colliding with the small asteroid Dimorphos. The intentional collision represents humanity's first attempt to change an asteroid's orbital trajectory, and a proof-of-concept experiment for anti-asteroid planetary defenses.
“Planetary defense is a globally unifying effort that affects everyone living on Earth,” said Thomas Zurbuchen, an associate administrator for the Science Mission Directorate at NASA. “Now we know we can aim a spacecraft with the precision needed to impact even a small body in space."
"Small body" is relative. Dimorphos has a diameter of about 530 feet and is estimated to weigh over 5.5 million tons, but it is still only a moonlet of the larger asteroid Didymos. This larger space rock, though not currently posing any threat to Earth, is considered a potentially hazardous near-Earth object with a diameter of about half a mile and an estimated mass of over 573 million tons.
The DART - short for Double Asteroid Redirection Test - probe, by contrast, weighed only about 1,260 pounds when it collided with Dimorphos on Monday at 7:14 p.m. Eastern time. To have the force necessary to alter Dimorphos' orbital trajectory around Didymos, it slammed into the moonlet travelling at around 14,000 mph. Even so, NASA scientists expect the collision will only shorten Dimorphos' orbit by roughly 1%, decreasing the time it takes to circle its larger partner by about 10 minutes.
Further observation will be needed to confirm whether DART's impact accomplished even that modest goal, and multiple ground and space-based telescopes are scheduled to observe the Didymos-Dimorphos binary system over the coming weeks and years.
The images the James Webb and Hubble telescopes captured of the impact are a first step in that observation process. Webb began recording Dimorphos with its infrared cameras shortly before DART's impact and continued to capture footage for about five hours afterward. The 10 resulting images show a bright impact core, from which plumes of dust and debris radiated out in a starburst pattern. The total brightness of the system tripled following the impact, and simultaneous visible-spectrum observations by Hubble showed that increased brightness held steady for hours.
Hubble observed the asteroid system for longer than Webb, capturing 45 images from both immediately before DART's impact and over the course of eight hours afterwards. Unlike Webb, the older telescope shot only in visible light, but NASA scientists said the data Hubble returned was no less valuable. It recorded the same starburst plumes of rock and dust that are visible in Webb's images and, eight hours post-impact, it also spotted a curvature in the plumes' trajectory indicating the direction from which DART approached Dimorphos.
“When I saw the data, I was literally speechless, stunned by the amazing detail of the ejecta that Hubble captured,” said Hubble observation lead Jian-Yang Li of the Planetary Science Institute in Tucson.
The combined footage from Webb and Hubble will help scientists learn more about Dimorphos' surface and how the DART impact affected it. The images will also be important for scientists to determine how much material was displaced by the impact, how fast that material was displaced, and whether the ejecta plumes are composed of mostly finer dust or larger chunks of material.
All this information will feed into the DART mission's larger objective: determining just how effectively a high-speed impact can - or can't - alter an asteroid's trajectory.
The coordinated effort to observe an asteroid collision with two separate telescopes in two separate spectrums of light is also a research success in and of itself. It's as much a first in space exploration as the DART impact, an "unprecedented view of an unprecedented event," as put by DART investigation lead Andy Rivkin.
“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," NASA Administrator Bill Nelson said in a prepared statement Thursday. "All of humanity eagerly awaits the discoveries to come from Webb, Hubble, and our ground-based telescopes – about the DART mission and beyond.”
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