Preparing a new way to see the universe

Webb Telescope L2 Flyby

The James Webb Space Telescope (JWST) is NASA’s next Great Observatories. Follow the lines of the Hubble Space Telescope, Compton Gamma Ray Observatory, Chandra X-ray Observatory, and Spitzer Space Telescope. JWST combines the two qualities of its predecessor, observing in infrared light like the Spitzer and observing in high resolution like the Hubble. Credits: NASA, SkyWorks Digital, Northrop Grumman, STScI

James Webb Space Telescope is finally ready to do science – and it’s seeing the universe more clearly than even its own engineers hoped for.

NASA is scheduled to release the first images taken by the James Webb Space Telescope on July 12, 2022. They’ll mark the beginning of the next era in astronomy as Webb – the largest space telescope ever built – begins 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 has taken nearly eight months of travel, setup, testing, and calibration to make sure this most valuable of telescopes is ready for prime time. Marcia Rieke, an astronomer at the University of Arizona and the scientist in charge of one of Webb’s four cameras, explains what she and her colleagues have been doing to get this telescope up and running.

1. What happened after the telescope was launched?

After the successful launch of the James Webb Space Telescope on December 25, 2021, the team will move the telescope to its final orbital position, deploy the telescope, and calibrate the onboard cameras and sensors as everything cools. Started a long process.

The launch went as smoothly as the rocket launch. One of the first things my NASA colleague noticed was that it was loaded with more fuel than expected to adjust the telescope’s orbit in the future. This will allow Webb to run much longer than the mission’s first 10-year goal.

The first task during the web’s one-month journey to its final location in orbit was to unfold the telescope. This started with a white sunshield knuckle deployment that helped cool the telescope, followed by mirror alignment and sensor on, and proceeded without problems.

When the sunshield opens, our team will start monitoring the temperature of the four cameras and spectrometers on board, low enough to start testing each of the 17 different modes in which the device can operate. I waited for the temperature to reach.


The NIRCam seen here measures infrared light from very distant and old galaxies. This was the first device to come online and helped align the 18 mirror segments. Credits: NASA / Chris Gunn

2. What did you test first?

Webb’s camera cooled as the engineers expected, and the first device the team turned on was a near-infrared camera (NIRCam). NIRCam is designed to study the faint infrared light produced by the oldest stars and galaxies in the universe. But before that was possible, NIRCam needed to help adjust the 18 individual segments of the Webb’s mirrors.

When the NIRCam cooled to minus 280F, it was cold enough to start detecting the light reflected by the Webb’s mirror segment and produce the first image of the telescope. The NIRCam team was ecstatic when the first bright image arrived. We were working!

These images show that the mirror segments all point to a relatively small area of ​​the sky, and the placement was much better than the worst-case scenario planned.

The web’s fine guidance sensor also worked during this time. This sensor helps keep the telescope steadily aimed at the target, much like image stabilization in consumer digital cameras. Using the Star HD84800 as a reference point, colleagues on the NIRCam team can dial the alignment of the mirror segment until it is virtually perfect, far better than the minimum required for a successful mission. I helped.

3. Which sensor was activated next?

When the mirror adjustments were completed on March 11, the Near Infrared Spectrograph – NIRSpec – and the Near Infrared Imager and Slitless Spectrograph – NIRISS – finished cooling and joined the party.

NIRSpec is designed to measure the intensity of light of different wavelengths 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 blocks other light.

NIRSpec has multiple slits that allow you to see 100 objects at once. Team members first tested multiple target modes, ordered the slits to open and close, and confirmed that the slits were responding correctly to the commands. In future steps, we will measure exactly where the slit is pointing and make sure that we can observe multiple targets at the same time.

NIRISS is a slitless spectroscope that decomposes light into different wavelengths, but is suitable for observing all objects in the field, not just the objects on the slit. It has several modes, including two specifically designed to study exoplanets close to their parent stars.

So far, equipment checks and calibrations have been successful, and the results show that both NIRSpec and NIRISS provide even better data than engineers expected before launch. ..

Comparison image of Webb MIRI and Spitzer

The MIRI camera in the image on the right allows astronomers to see through a cloud of dust with incredible clarity compared to earlier telescopes such as the Spitzer Space Telescope that produced the image on the left. Credits: NASA / JPL-Caltech (left), NASA / ESA / CSA / STScI (right)

4. What was the last device you turned on?

The last device launched by Webb was the Mid-Infrared Device (MIRI). MIRI is designed to take pictures of distant or newly formed galaxies and faint small objects such as asteroids. This sensor must be kept at minus 449 F (11 degrees Fahrenheit) to detect the longest wavelength of Webb equipment.[{” attribute=””>absolute zero. If it were any warmer, the detectors would pick up only the heat from the instrument itself, not the interesting objects out in space. MIRI has its own cooling system, which needed extra time to become fully operational before the instrument could be turned on.

Radio astronomers have found hints that there are galaxies completely hidden by dust and undetectable by telescopes like Hubble that captures wavelengths of light similar to those visible to the human eye. The 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 the 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 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 just three to go.

On July 12, NASA plans to release a suite of teaser observations that illustrate Webb’s capabilities. These will show the beauty of Webb imagery and also give astronomers a real taste of the quality of data they will receive.

After July 12, the James Webb Space Telescope will start working full time on its science mission. The detailed schedule for the coming year hasn’t yet been released, but astronomers across the world are eagerly waiting to get the first data back from the most powerful space telescope ever built.

Written by Marcia Rieke, Regents Professor of Astronomy, University of Arizona.

This article was first published in The Conversation.The Conversation

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