Two weeks until launch! Things are moving forward in Kourou, and so we check in with the two leads (one from the U.S., one from the U.K.) of the final instrument in Webb’s suite:
“Webb’s Mid-Infrared Instrument (MIRI) is special – in the wavelengths it covers, the science that enables, its technology challenges, and in the way it was built.
“With the other three instruments, Webb observes wavelengths up to 5 microns. Adding wavelengths out to 28.5 microns with MIRI really increases its range of science. This includes everything from studying protostars and their surrounding protoplanetary disks, the energy balance of exoplanets, mass loss from evolved stars, circumnuclear tori around the central black holes in active galactic nuclei, and a lot more.
“The universe is relatively unexplored at mid-infrared wavelengths. Since anything at room temperature emits mid-infrared light, infrared astronomers working with ground-based telescopes peer through the huge foreground infrared emission of the telescope and atmosphere. With perseverance, some interesting mid-infrared results have been obtained from ground-based telescopes, but the limitations are severe.
“Dramatic results in the mid-infrared have come from telescopes in the vacuum of space, where they are cooled to cryogenic temperatures to eliminate their emission and are clear of Earth’s atmosphere. This brings big technical challenges. To keep the ice off the telescope before it was launched, the first infrared telescopes in space were built into thermos flasks, or Dewars, with thick walls to hold a vacuum. This meant that these telescopes had to be small, around a tenth the diameter of Webb. Despite their small size, these telescopes were very sensitive and have surveyed the entire sky as well as conducted pioneering studies of individual sources.
“Webb is built on a scale approaching the largest telescopes on the ground, and it will be cold enough to provide the full potential for the mid-infrared. The sensitivity gains and the image clarity will both be nearly a factor of 100 better than ever before. This was so exciting that ten European countries plus the United States pooled resources to make MIRI possible. The National Space Agencies of these ten European countries committed additional funding, beyond their ESA membership, specifically to build MIRI and enable its compelling science.
“While Webb provides the kind of capabilities in the mid-infrared that have only been dreamt of since the beginnings of infrared astronomy, we could only fit a single mid-infrared instrument into Webb and the available international resources. So, we designed the MIRI optics to cover almost everything – imaging, low- and medium-resolution spectroscopy, and high-contrast coronagraphy. About a third of the space for MIRI is empty to allow for long, thermally-isolating hexapod legs. MIRI includes a helium-filled closed-cycle cryogenic refrigerator to bring it to an operating temperature 33 degrees colder than the rest of Webb, reaching less than 7 degrees above absolute zero.
“Our multinational, transatlantic team has pulled together for more than two decades, with both exciting additions and painful losses, to provide Webb and the astronomical community with a mid-infrared instrument. Finally, the moment has arrived when the scientific results will reward everyone who has contributed. The instrument is ready, our cooler is full of helium and connected up, and the team is raring to go.”
—George Rieke, professor of astronomy at the University of Arizona, and Gillian Wright, director of the UK Astronomy Centre
By Jonathan Gardner, Webb deputy senior project scientist, NASA’s Goddard Space Flight Center
And Alexandra Lockwood, project scientist for Webb science communications, Space Telescope Science Institute