TYB
Webb’s Icy Instrument Reveals Complex Structures
27 September 2022, 06:00
This spectacular image features the spiral galaxy IC 5332, shown here in unprecedented detail thanks to observations from the Mid-InfraRed Instrument (MIRI), which is mounted on the NASA/ESA/CSA James Webb Space Telescope. IC 5332 lies over 29 million light-years from Earth, and has a diameter of roughly 66 000 light-years, making it about a third smaller than the Milky Way. It is notable for being almost perfectly face-on with respect to Earth, allowing us to admire the symmetrical sweep of its spiral arms.
MIRI is the only Webb instrument that is sensitive to the mid-infrared region of the electromagnetic spectrum (specifically in the 5 µm – 28 µm wavelength range); Webb’s other instruments all operate in the near-infrared. One of MIRI’s most remarkable features is that it operates 33 °C below the rest of the observatory at the frosty temperature of –266 °C. That means that MIRI operates in an environment only 7 °C warmer than absolute zero, which is the lowest possible temperature according to the laws of thermodynamics. MIRI requires this frigid environment in order for its highly specialised detectors to function correctly, and it has a dedicated active cooling system to ensure that its detectors are kept at the correct temperature.
It is worth noting just how challenging it is to obtain observations in the mid-infrared region of the electromagnetic spectrum. The mid-infrared is incredibly difficult to observe from Earth as much of it is absorbed by Earth’s atmosphere, and heat from Earth’s atmosphere further complicates things. Hubble could not observe the mid-infrared region as its mirrors were not cool enough, meaning that infrared radiation from the mirrors themselves would have dominated any attempted observations. The extra effort made to ensure that MIRI’s detectors had the freezing environment necessary to operate properly is evident in this stunning image.
This extravagantly detailed mid-infrared image is juxtaposed here with a beautiful ultraviolet and visible-light image of the same galaxy, created using data collected by Hubble’s Wide Field Camera 3 (WFC3). Some differences are immediately obvious. The Hubble image shows dark regions that seem to separate the spiral arms, whereas the Webb image shows more of a continual tangle of structures that echo the spiral arms’ shape. This difference is due to the presence of dusty regions in the galaxy. Ultraviolet and visible light are far more prone to being scattered by interstellar dust than infrared light. Therefore dusty regions can be identified easily in the Hubble image as the darker regions that much of the galaxy’s ultraviolet and visible light has not been able to travel through. Those same dusty regions are no longer dark in the Webb image, however, as the mid-infrared light from the galaxy has been able to pass through them. Different stars are visible in the two images, which can be explained because certain stars shine brighter in the ultraviolet, visible and infrared regimes respectively. The images complement one another in a remarkable way, each telling us more about IC 5332’s structure and composition.
https://esawebb.org/images/comparisons/potm2209a/
Webb, Hubble Capture Detailed Views of DART Impact
Sep 29, 2022
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 observations of NASA’s Double Asteroid Redirection Test (DART) impact mark the first time that Webb and Hubble simultaneously observed the same celestial target.
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.
“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. “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.”
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 Captures Impact Site Before and After Collision
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.
“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.”
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.
Webb observed the impact over five hours total and captured 10 images. The data was collected as part of Webb’s Cycle 1 Guaranteed Time Observation Program 1245 led by Heidi Hammel of the Association of Universities for Research in Astronomy (AURA).
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Hubble Images Show Movement of Ejecta After Impact
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.
“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 captured 45 images in the time immediately before and following DART’s impact with Dimorphos. The Hubble data was collected as part of Cycle 29 General Observers Program 16674.
“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.
https://www.nasa.gov/feature/goddard/2022/webb-hubble-capture-detailed-views-of-dart-impact
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