The James Webb Space Telescope (JWST) is next to NASA’s Great Observatory; following the line of the Hubble Space Telescope, the Compton Gamma Ray Observatory, the Chandra X-Ray Observatory, and the Spitzer Space Telescope. JWST combines the qualities of two of its predecessors, observing in infrared light, like Spitzer, with a fine resolution, like Hubble. Credits: NASA, SkyWorks Digital, Northrop Grumman, STScI
NASA’s James Webb Space Telescope is finally ready to do science, and it is seeing the universe more clearly than even its own engineers expected.
NASA plans to release the first images taken by the James Webb Space Telescope on July 12, 2022. They will mark the beginning of the next astronomy era when Webb, the largest space telescope ever built, begins collecting scientific data that will help answer questions about the first moments of the universe and allow astronomers to study exoplanets in more detail than ever before. But it has taken almost eight months of travel, setup, testing and calibration to make sure this most valuable telescope is ready for prime time. Marcia Rieke, an astronomer at the University of Arizona and a scientist in charge of one of Webb’s four cameras, explains what she and her colleagues have been doing to launch this telescope.
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, deploying the telescope and, as everything cooled, calibrating the cameras and sensors on board.
The launch was as good as a rocket launch. 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 run for much longer than the initial 10-year mission goal.
The first task during Webb’s month-long journey to its final location in orbit was to deploy the telescope. This went smoothly, beginning with the deployment of the white shield of the solar shield that helps cool the telescope, followed by the alignment of the mirrors and the lighting of the sensors.
Once the parasol was opened, our team began monitoring the temperatures of the four cameras and spectrometers on board, waiting for them to reach temperatures low enough to begin testing each of the 17 different modes in which the instruments can operate.
NIRCam, seen here, will measure the infrared light of very distant and ancient galaxies. It was the first instrument to be connected and helped align the 18 segments of the mirror. Credit: NASA / Chris Gunn
2. What did you try first?
Webb’s cameras cooled as predicted by engineers, and the first instrument the computer turned on was the nearby infrared camera, or NIRCam. NIRCam is designed to study the light infrared light produced by the oldest 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 cold enough to begin detecting the light reflected from the segments of Webb’s mirror and producing the first images of the telescope. The NIRCam team was thrilled when the first light image arrived. We were in business!
These images showed that all segments of the mirror pointed to a relatively small area of the sky and the alignment was much better than the worst-case scenarios we had predicted.
Webb’s thin guide sensor also came into operation at this time. This sensor helps keep the telescope pointing steadily at a target, such as image stabilization in digital consumer cameras. Using the HD84800 star as a benchmark, my NIRCam teammates helped mark the alignment of the mirror segments until it was virtually perfect, far better than the bare minimum needed for a successful mission.
3. Which sensors came to life later?
When the mirror alignment ended on March 11, the Near Infrared Spectrograph (NIRSpec) and the Near Infrared Imager and Slitless Spectrograph (NIRISS) finished cooling off and joined the party.
NIRSpec is designed to measure the strength of different wavelengths of light from a target. This information may reveal the composition and temperature of distant stars and galaxies. NIRSpec does this by looking at its target through a slot that keeps the other light out.
NIRSpec has multiple slots that allow you to look at 100 objects at once. Team members began testing the multi-target mode, ordering the slots to open and close, and confirmed that the slots responded correctly to commands. Future steps will measure exactly where the cracks point and check that several targets can be observed simultaneously.
NIRISS is a slotless spectrograph that will also break light at its different wavelengths, but it is best to look at all objects in a field, not just those in the slots. It has several modes, including two specifically designed to study exoplanets especially close to its parent stars.
So far, testing and calibration of the instruments has gone smoothly, and the results show that both NIRSpec and NIRISS will provide even better data than engineers predicted before launch.
The MIRI camera, pictured on the right, allows astronomers to see through dust clouds with incredible sharpness compared to previous telescopes such as the Spitzer Space Telescope, which produced the image on the left. Credit: NASA / JPL-Caltech (left), NASA / ESA / CSA / STScI (right)
4. What was the last instrument to light?
The last instrument to boot 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 such as asteroids. This sensor detects the longest wavelengths of Webb instruments and must be kept at minus 449 F, only 11 degrees F above absolute zero. If it were warmer, the detectors would only capture the heat of the instrument itself, not the interesting objects in space. MIRI has its own cooling system, which needed more time to be fully operational before the instrument could be turned on.
Radio astronomers have found evidence that there are galaxies completely hidden by dust and undetectable by telescopes like Hubble that capture light wavelengths similar to those visible to the human eye. Extremely low temperatures allow MIRI to be incredibly sensitive to light in the mid-infrared range that 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 the stars and structures of these galaxies for the first time.
5. What’s next for Webb?
As of June 15, 2022, all of Webb’s instruments are on and have made their first images. In addition, four imaging modes, three time series modes, and three spectroscopic modes have been tested and certified, leaving only three.
On July 12, NASA plans to launch a set of teaser observations illustrating Webb’s capabilities. These will show the beauty of Webb’s images and also give astronomers a real taste of the quality of the data they receive.
After July 12, the James Webb Space Telescope will begin full-time work on its scientific mission. The detailed calendar for next year has not yet been published, but astronomers around the world are looking forward to retrieving the first data from the most powerful space telescope ever built.
Written by Marcia Rieke, Regents Professor of Astronomy at the University of Arizona.
This article was first published in The Conversation.