NASA is set to release the first images taken by the James Webb Space Telescope on July 12, 2022. They will mark the start of the next era of astronomy as Webb – the largest space telescope ever built – begins collecting scientific data that will will help answer questions about the earliest moments of the universe and allow astronomers to study exoplanets in greater detail than ever before. But it took almost eight months of travel, setup, testing and calibration to ensure this most valuable telescope is ready for prime time. Marcia Rieke, astronomer at the University of Arizona and the scientist in charge of one of Webb’s four cameras, explains what she and her colleagues did to get this telescope going.
1. What has happened since the launch of the telescope?
Following the successful launch of the James Webb Space Telescope on December 25, 2021, the team began the long process of moving the telescope to its final orbital position, unfolding the telescope, and – as everything cooled – calibrating the cameras and on-board sensors.
The launch went as smoothly as a rocket launch can go. One of the first things my NASA colleagues noticed was that the telescope had more fuel on board than expected to make future adjustments to its orbit. This will allow Webb to work much longer than the mission’s original 10-year goal.
The first task on Webb’s month-long journey to its final location in orbit was to unfold the telescope. It went off without a hitch, starting with the breathless deployment of the sun visor which helps cool the telescope, followed by aligning the mirrors and turning on the sensors.
Once the sun visor was opened, our team began monitoring the temperatures of the four cameras and spectrometers on boardwaiting for them to reach temperatures low enough that we can start testing each of the 17 different modes in which instruments can operate.
2. What did you test first?
Webb’s cameras cooled as the engineers had predicted, and the first instrument the team turned on was the Near Infrared Camera – or NIRCam. NIRCam is designed to study the faint infrared light produced by older stars or galaxies In the universe. But before it could do that, NIRCam had to help align the 18 individual segments of Webb’s mirror.
Once NIRCam cooled to minus 280 F, it was cool enough to begin detecting light reflected from Webb’s mirror segments and producing the telescope’s first images. The NIRCam team was thrilled when the first bright image arrived. We were in business!
These images showed that the mirror segments were all pointing to a relatively small area of the skyand the lineup was much better than the worst-case scenarios we had anticipated.
Webb’s fine guidance sensor also entered service at this time. This sensor helps keep the telescope pointed steadily at a target, much like the image stabilization in consumer digital cameras. Using the HD84800 star as a reference point, my colleagues from the NIRCam team helped dial in the alignment of the mirror segments until it was nearly perfect, much better than the minimum required for a successful mission.
3. Which sensors then came to life?
As the mirror alignment wrapped up on March 11, the Near Infrared Spectrograph – NIRSpec – and the Near Infrared Imager and Slitless Spectrograph – NIRISS – finished cooling down and joined the party.
NIRspec is designed to measure the strength of different wavelengths of light from a target. This information can reveal the composition and temperature of distant stars and galaxies. NIRSpec does this by looking at its target object through a slit that blocks all other light from entering.
NIRspec has several slots that allow it to look at 100 objects at once. Team members started by testing the multi-target mode, commanding the slits to open and close, and they confirmed that the slits responded correctly to commands. The next steps will measure exactly where the slits are pointing and verify that multiple targets can be observed simultaneously.
NIRISS is a slitless spectrograph that will also break light into its different wavelengths, but is better at observe all objects in a field, not just those on slits. It has several modes, including two specially designed to study exoplanets particularly close to their parent stars.
So far, instrument checks and calibrations have gone smoothly, and the results show that NIRSpec and NIRISS will deliver even better data than what engineers predicted before launch.
4. What was the last instrument to light up?
The last instrument to start on Webb was the Mid-Infrared Instrument, or MIRI. MIRI is designed to take pictures of distant or newly formed galaxies as well as small faint objects like asteroids. This sensor detects the longest wavelengths of Webb’s instruments and should be maintained at minus 449 F – just 11 degrees F above absolute zero. If it were warmer, the detectors would only pick up heat from the instrument itself, not the objects of interest in space. MIRI has its own cooling systemwhich needed more time to become fully operational before the instrument could be turned on.
Radio astronomers have found clues that there are galaxies completely hidden by dust and undetectable by telescopes like Hubble which captures wavelengths of light similar to those visible to the human eye. Extremely cold temperatures allow MIRI to be incredibly sensitive to light in the mid-infrared range which can pass through dust more easily. When this sensitivity is combined with Webb’s large mirror, it allows MIRI to penetrate these dust clouds and reveal stars and structures in such galaxies for the first time.
5. What’s next for Webb?
As of June 15, 2022, all of Webb’s instruments have been turned on and taken their first images. Additionally, four imaging modes, three time series modes, and three spectroscopic modes have been tested and certified, with only three remaining.
On July 12, NASA plans to post a suite of teaser observations which exemplify Webb’s abilities. These will show the beauty of the Webb images and will also give astronomers a real insight into the quality of the data they will be receiving.
After July 12, the James Webb Space Telescope will begin full-time work on its science mission. A detailed schedule for the coming year has yet to be released, but astronomers around the world are eagerly awaiting the first data from the most powerful space telescope ever built.
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