Stunning Image Marks Another Milestone for JWST

Stunning Image Marks Another Milestone for JWST

The James Webb Space Telescope has marked another milestone as it proceeds through several months of commissioning before it is ready for scientific operations. Today NASA released the first crisp image of a star demonstrating that the 18 segments of the telescope’s primary mirror are now correctly aligned. Scientific-quality images are still a few months away, but this one whets the appetite of what’s to come.

The $10 billion telescope, a joint project of NASA, the European Space Agency, and the Canadian Space Agency, arrived at its final destination on January 24, almost exactly a month after its Christmas Day launch. During the journey, it unfolded itself, deploying a solar array, a sunshield, the 18-segment primary mirror, and the secondary mirror on a tripod structure.

Infrared light is collected by the James Webb Space Telescope’s gold-plated primary mirror, reflected into the secondary mirror at the end of the tripod-structure (covered in black) and directed back into the four instruments in the center of the primary mirror. Credit: NASA representation using its Observatory Visualization Tool.

Each of the 18 gold-plated segments has seven actuators behind it to correctly shape the surface to receive infrared radiation and form a single, sharp image instead of 18 fuzzy ones. The radiation is reflected into the secondary mirror (which also has actuators) at the end of the tripod and then back into the four instruments in the center of the primary mirror.

Today NASA announced that the segments are now finely tuned and seeing a single, clear image through the Near Infrared Camera (NIRCam), the first of the four instruments to begin operations.

Thomas Zurbuchen, NASA’s Associate Administrator for the Science Mission Directorate, told reporters that this is “one of the most magnificent days in my career at NASA” because “we can announce that the optics will perform to specifications or even better. It’s an amazing achievement.”

They picked an ordinary star that just happened to be in the right place for the tests. The result is spectacular.

While the purpose of this image was to focus on the bright star at the center for alignment evaluation, Webb’s optics and NIRCam are so sensitive that the galaxies and stars seen in the background show up. At this stage of Webb’s mirror alignment, known as “fine phasing,” each of the primary mirror segments have been adjusted to produce one unified image of the same star using only the NIRCam instrument. This image of the star, which is called 2MASS J17554042+6551277, uses a red filter to optimize visual contrast. Image and caption credits: NASA/STScI

The goal was just to image the star, but JWST is so sensitive that it also picked up galaxies and stars behind it. For comparison, Marshall Perrin of the Space Telescope Science Institute said the star is 100 times fainter than what the human eye can see. STScI operates JWST as well as the 32-year-old Hubble Space Telescope.

Aligning the mirrors is still just a step. Several more months are needed to activate the other instruments and “unleash the power of this new observatory,” Zurbuchen cautioned.

JWST is an infrared telescope, which means the instruments must be very cold to detect the heat signatures of celestial objects. Three of the instruments — NIRCam, the Near-Infrared Spectrograph (NIRSpec), and the Fine Guidance Sensor/Near InfraRed Imager and Slitless Spectrograph (FGS/NIRISS) — operate at 40 Kelvin (-387°F/-233°C). That temperature can be achieved passively by exposing them to space environment. The fourth, the Mid-Infrared Instrument (MIRI), must be even colder, 7 K (-447°F/-266°C), and needs an active cooling system.

NIRCam was provided by the University of Arizona, NIRSpec by ESA, MIRI jointly by NASA and the European Consortium (led by the U.K.) with ESA, and FGS/NIRISS by Canada.

After successfully deploying the telescope and aligning the mirrors, Zurbuchen and others at today’s briefing were asked if any potential showstoppers lie ahead. Zurbuchen replied that “all the sleepless nights I’ve had and the worries I’ve had, they’re all behind us now.” Not that everything is done. There’s still “a mountain to climb … but we’re way up that mountain now.”

Jane Rigby, Webb operations project scientist at NASA’s Goddard Space Flight Center, said she’s keeping an eye on cooling MIRI. It’s now at 90°K and needs to get down to 7°K using basically a “closed circuit refrigerator that recirculates helium.” But broadly speaking, at this point if something doesn’t work as planned it would mean a “gradual degradation” of the data that’s gathered, not “show’s over, folks” as would have been the case if deployment or alignment failed.

The first scientific-quality images are expected in late June or July. NASA and STScI are keeping the target for that first image under wraps for now, but the entire first year of observations already have been selected.

That will be the first of perhaps as many as 20 years. JWST officially has a design life of 5 years, but the goal was 10 years and enough fuel was loaded so it could maintain its orbit around the Sun-Earth Lagrange Point-2 (SEL-2) for that duration. Europe’s Ariane 5 rocket put it on such precise trajectory, however, that less fuel than anticipated was needed to get to SEL-2, meaning more remains for stationkeeping. NASA is not making official predictions yet, but word is that 20 years is not out of the question.


Correction: The original article referred to degrees (°) Kelvin, but temperatures in Kelvin do not reference degrees because it is an absolute scale where zero is absolute zero.

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