![]() ![]() By peering through even thicker clouds of dust than the near-infrared instruments, MIRI will reveal the birthplaces of stars. Webb's Near-Infrared Camera, or NIRCam instrument, will be able to detect these extremely distant objects, and MIRI will help scientists confirm that these faint sources of light are clusters of first-generation stars, rather than second-generation stars that form later as a galaxy evolves. One of Webb's big science goals will be to study the properties of the first generation of stars to form in the universe. So those are the challenges we faced, and in that respect, I would say the MIRI cryocooler is certainly at the cutting edge." For a space observatory, we need a cooler that is physically compact, highly energy efficient, and it has to be highly reliable because we can't go out and repair it. "But those Earth-based systems are very bulky and energy inefficient. "It's relatively easy to cool something down to that temperature on Earth, typically for scientific or industrial applications," said Konstantin Penanen, a cryocooler specialist at NASA's Jet Propulsion Laboratory in Southern California, which manages the MIRI instrument for NASA. Beginning about 77 days after launch, MIRI's cryocooler will spend 19 days lowering the temperature of the instrument's detectors to less than 7 kelvins. After launch, Webb will unfold a tennis-court-size sunshield that will block MIRI and the other instruments from the Sun's heat, allowing them to cool passively. These unwanted signals are what astronomers refer to as "noise," and they can overwhelm the faint signals that Webb is trying to detect. As a result, its detectors are even more sensitive to thermal vibrations. ![]() MIRI detects light in a lower-energy range than the other three instruments. Temperature is essentially a measurement of how fast atoms are moving, and in addition to detecting their own infrared light, the Webb detectors can be trigged by their own thermal vibrations. ![]() (MIRI is not, however, the coldest imaging instrument ever to operate in space.) That's just a few degrees above absolute zero (0 kelvins) – the coldest temperature theoretically possible, though it's never physically attainable because it represents the total absence of any heat. But to operate properly, the detectors inside the mid-infrared instrument, or MIRI, will have to get even colder: less than 7 kelvins (minus 448 degrees Fahrenheit, or minus 266 degrees Celsius). To reduce those emissions, the instruments have to be really cold – about 40 kelvins, or minus 388 degrees Fahrenheit (minus 233 degrees Celsius). That means Webb's four infrared instruments can detect their own infrared glow. But so do most other warm objects, like toasters, humans, and electronics. Many cosmic objects – including stars and planets, as well as the gas and dust from where they form – emit infrared light, sometimes called heat radiation. 22, NASA's James Webb Space Telescope is the largest space observatory in history, and it has an equally gargantuan task: to collect infrared light from the distant corners of the cosmos, enabling scientists to probe the structures and origins of our universe and our place in it. December 14, 2021: Before the MIRI instrument – one of four scientific instruments aboard the observatory – can operate, it has to be cooled down to almost the coldest temperature matter can reach.Figure 2: Webb encapsulated inside Ariane 5 (image credit: ESA, Manuel Pedoussaut)
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