This article was originally published on The conversation. (opens in new tab) The publication contributed the article to Space.com magazine. Expert Voices: Op-Ed and Insights.
Marcia Rieke (opens in new tab)Regents Professor of Astronomy, University of Arizona
NASA is scheduled to release the first images taken by the James Webb Space Telescope on July 12, 2022.
They will mark the beginning of the next era in astronomy when Webb – the largest space telescope ever built – begins collecting scientific data that will help answer questions about the universe’s earliest moments and allow astronomers to study exoplanets in more detail than ever before. . But it took nearly eight months of travel, setup, testing and calibration to ensure this most valuable of telescopes is ready for prime time.
Marcia Rieke, astronomer at the University of Arizona (opens in new tab) and the scientist responsible for one of Webb’s four cameras, explains what she and her colleagues have been doing to get this telescope up and running.
Related: NASA’s James Webb Space Telescope Mission: Live updates
1. What happened since the launch of the telescope?
After 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 down – calibrating the cameras and sensors. on board.
The launch was as smooth as a rocket launch can get. One of the first things my colleagues at NASA noticed was that the telescope had more fuel left on board than anticipated to make future adjustments to its orbit. This will allow the Webb to operate much longer. (opens in new tab) 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 off without a hitch, starting with the deployment of the sun shield. (opens in new tab) which helps to cool the telescope, followed by aligning the mirrors and activating the sensors.
Once the sunscreen was open, our team began monitoring the temperatures of the four cameras and spectrometers on board. (opens in new tab)waiting for them to reach temperatures low enough that we could start testing each of the 17 different modes the instruments can operate in. (opens in new tab).
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2. What did you test first?
The cameras on the Webb cooled down just as the engineers predicted, and the first instrument the team turned on was the Near Infrared Camera – or NIRCam. NIRCam was designed to study the faint infrared light produced by older stars or galaxies. (opens in new tab) in the universe. But before it could do that, NIRCam had to help align the 18 individual segments of the Webb mirror.
Once NIRCam cooled to minus 280 degrees Fahrenheit, 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 ecstatic when the first light image arrived. We were in business!
These images showed that the mirror segments were all pointing to a relatively small area of the sky. (opens in new tab)and the alignment was much better than the worst-case scenarios we had planned.
Webb’s fine orientation sensor also came into operation at this time. This sensor helps keep the telescope firmly pointing at a target – much like image stabilization in consumer digital cameras. Using the HD84800 star as a reference point, my colleagues on the NIRCam team helped dial in the alignment of the mirror segments until it was virtually perfect, far better than the bare minimum needed for a successful mission. (opens in new tab).
3. Which sensors came to life next?
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 (opens in new tab) coming from a target. This information can reveal the composition and temperature of distant stars and galaxies. NIRSpec does this by looking at the target object through a slit that keeps light out.
NIRSpec has multiple slits that allow you to look at 100 objects at once (opens in new tab). Team members began testing the multi-target mode, commanding the rifts to open and close, and confirmed that the rifts were responding correctly to commands. Future steps will measure exactly where the slits are pointing and verify that multiple targets can be observed simultaneously. (opens in new tab).
NIRISS is a slitless spectrograph that also breaks light into its different wavelengths, but is better for observing all objects in a field, not just the ones in the slits. (opens in new tab). It has several modes, including two specifically designed to study exoplanets particularly close to their parent stars.
So far, instrument checks and calibrations are going smoothly, and the results show that both NIRSpec and NIRISS will provide even better data than engineers predicted before launch.
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4. What was the last instrument to be turned on?
The final instrument to boot into 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 longer wavelengths of Webb instruments and should be kept at minus 449 degrees Fahrenheit (minus 267 degrees Celsius) – just 11 degrees F above absolute zero. If it were warmer, the detectors would only pick up the heat from the instrument itself, not the interesting objects in space. MIRI has its own cooling system (opens in new tab)that needed extra time to become fully operational before the instrument could be turned on.
Radio astronomers have discovered evidence that galaxies exist completely hidden by dust and undetectable by telescopes like Hubble. (opens in new tab) that captures wavelengths of light similar to those visible to the human eye. The extremely low 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 the stars and structures. (opens in new tab) in such galaxies for the first time.
5. What’s Next for Webb?
As of June 15, 2022, all Webb instruments are turned on and have taken 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 release a set of teaser observations (opens in new tab) that illustrate Webb’s capabilities. This will show the beauty of the Webb images and will also give astronomers a real taste of the quality of the data they will receive.
After July 12, the James Webb Space Telescope will begin full-time work on its science mission. The detailed timeline for next year has yet to be released, but astronomers around the world are eagerly waiting to get the first data from the most powerful space telescope ever built.
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