The James Webb Space Telescope is ready to do science: it will show you the Universe as you never imagined it

NASA is set to release the first images taken by the James Webb Space Telescope July 12, 2022. They will usher in the next era of astronomy when the largest space telescope ever built, begin collecting scientific data that 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 nearly eight months of travel, installation, testing and calibration to ensure this most valuable telescope is ready for prime time.

Marcia Rieke, an astronomer at the University of Arizona and scientist in charge of one of Webb’s four cameras, explains what she and her colleagues have done to make this telescope operational.

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, deploying it, and while everything cooled, calibrate cameras and sensors on board.

Launch picture. Photo: AFP

The launch was as smooth as a rocket launch can be. 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 operate much longer than the mission’s original 10-year goal.

The first task during Webb’s month-long journey to its final orbital location was to unfold the telescope. It went off without a hitch, starting with the white-hinged deployment of the sunshade which helps cool the telescope, followed by aligning the mirror and powering up the sensor.

Once the sunscreen is opened, our team began monitoring the temperatures of the four onboard cameras and spectrometers, hoping they would reach temperatures low enough that we could begin testing each of the 17 different modes the instruments can operate in.

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 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 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 appeared. We were in business!

Scientists during the manufacture of the NIRCam camera. Photo: NASA

These images showed that all of the mirror segments were pointing to a relatively small area of ​​the sky, and the alignment was much better than the worst-case scenarios we had anticipated.

Webb’s Fine Guidance Sensor also went live at this time. This sensor helps keep the telescope constantly pointed at a target, much like the image stabilization in conventional digital cameras. Using the HD84800 star as a reference point, my colleagues from the NIRCam team helped tune the alignment of the mirror segments until it was near perfect, far better than the minimum required for a successful mission. .

When the mirror alignment was completed on March 11, the Near Infrared Spectrograph (NIRSpec) and 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 coming 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 light.

NIRSpec has multiple slots that allow you to view 100 objects at once. Team members began by testing multi-target mode, commanding the slits to open and close, and 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.

The James Webb Telescope in its assembly process. Photo: NASA

NIRISS is a slitless spectrograph that will split light equally into its different wavelengths, but it’s best to look at all objects in a field, not just those in the slits. It has several modes, including two specially designed to study exoplanets particularly close to their parent stars.

Until now, instrument checks and calibrations were carried out without problems and the results show that NIRSpec and NIRISS will deliver even better data than engineers predicted before launch.

The last instrument to be commissioned at 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 interesting objects in space. MIRI has its own cooling system, which took longer to become fully operational before the instrument could be powered on.

Radio astronomers have found indications that there are galaxies completely hidden by dust and undetectable by telescopes like Hubble, which capture 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 the Large Webb Mirror, it allows MIRI to penetrate these dust clouds and reveal the stars and structures of these galaxies for the first time.

As of June 15, 2022, all of Webb’s instruments are on and have taken their first images. Additionally, four imaging modes, three time series modes and three spectroscopic modes have been tested and certified, leaving only three for last.

On July 12, NASA plans to release a set of preliminary observations illustrating Webb’s capabilities. These will show the beauty of Webb’s images and 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 next 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.

*Marcia Rieke, astronomer at the University of Arizona and scientist in charge of one of the four cameras of the James Webb Telescope

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