The Incredibly Cool James Webb Space Telescope

The Incredibly Cool James Webb Space Telescope 1

By Lambert Strether of Corrente.

As an engineering project, the James Webb Space Telescope (JWST) is, in fact, incredibly cool:

Being an exquisitely sensitive infrared astronomical observatory, the James Webb Space Telescope’s optics and scientific instruments need to be cold to suppress infrared background “noise.” Moreover, the detectors inside each scientific instrument, that convert infrared light signals into electrical signals for processing into images, need to be cold to work just right. Typically, the longer the wavelength of infrared light, the colder the detector needs to be to do this conversion while also limiting the generation of random “noise” electrons.

I totally identity with that; I have to suppress a lot of random “noise” electrons myself; it’s called the “news flow.” But why so cold?

The low temperature is necessary because all four of Webb’s instruments detect infrared light – wavelengths slightly longer than those that human eyes can see. Distant galaxies, stars hidden in cocoons of dust, and planets outside our solar system all emit infrared light. But so do other warm objects, including Webb’s own electronics and optics hardware. Cooling down the four instruments’ detectors and the surrounding hardware suppresses those infrared emissions. MIRI detects longer infrared wavelengths than the other three instruments, which means it needs to be even colder.

Another reason Webb’s detectors need to be cold is to suppress something called dark current, or electric current created by the vibration of atoms in the detectors themselves. Dark current mimics a true signal in the detectors, giving the false impression that they have been hit by light from an external source. Those false signals can drown out the real signals astronomers want to find. Since temperature is a measurement of how fast the atoms in the detector are vibrating, reducing the temperature means less vibration, which in turn means less dark current.

Yes, yes, “dark currents.” That tracks. Anyhow, the JWST has cooled down enough, and now that it has, we have photos! This is going to be an extremely lazy post, a mere excuse to post as many beautful JWST photos as I can find (hopefully different ones from the mainstream). Let’s go!

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But wait. Let’s not.

I must also confess that I expected a JWST debacle; I well remember the day when the “mirror flaw” of the Hubble Telescope, another Pharonic project, was discovered: “[T]he observatory’s primary mirror had an aberration that affected the clarity of the telescope’s early images.” My first thought: “We can’t manufacture anything anymore.” A reasonably advanced thought for 1990, I think, and a thought that I and many others have had since. Fortunately, however, there was no JWST debacle, which really did give me some hope and confidence that the country wasn’t going to screw literally everything up. Here is a photo that shows what a glorious piece of machinery the JWST is (and by extension, the glory of its builders):

The Incredibly Cool James Webb Space Telescope 2

The link above gives a good description of the JWST instrumentation, but here is an explanation of how JWST’s iconic Primary Mirror, the golden hexagonalized construct seen at bottom center above, was engineered:

Webb Telescope’s scientists and engineers determined that a primary mirror 6.5 meters (21 feet 4 inches) across is what was needed to measure the light from these distant galaxies.

The Webb Telescope team also decided to build the mirror in segments on a structure which folds up, like the leaves of a drop-leaf table, so that it can fit into a rocket. The mirror would then unfold after launch. Each of the 18 hexagonal-shaped mirror segments is 1.32 meters (4.3 feet) in diameter, flat to flat.

The hexagonal shape allows for a roughly circular, segmented mirror with “high filling factor and six-fold symmetry.” High filling factor means the segments fit together without gaps. If the segments were circular, there would be gaps between them. Symmetry is good because there need only be 3 different optical prescriptions for 18 segments, 6 of each (see above right diagram). Finally, a roughly circular overall mirror shape is desired because that focuses the light into the most compact region on the detectors. A oval mirror, for example, would give images that are elongated in one direction. A square mirror would send a lot of the light out of the central region.

Gold improves the mirror’s reflection of infrared light.

(There’s a lot more information at the link above on the JWST’s mirrors.) If you’ve got four hours, here’s a video of the primary mirror’s unfolding (“deployment”):

And segments of the mirror itself, “in the cleanroom at NASA Goddard, was captured in the spring of 2017, before the telescope was transported to NASA Johnson for cryogenic testing”:

The Incredibly Cool James Webb Space Telescope 3

Well, enough about the engineering; sorry to fall into squeeing fan boy mode, there; something I hope I rarely do. Now, to the photos. Let’s go!

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The Incredibly Cool James Webb Space Telescope 4

Humanity’s Last Glimpse of the James Webb Space Telescope “Here it is: humanity’s final look at the James Webb Space Telescope as it heads into deep space to answer our biggest questions…. This image was captured by the cameras on board the rocket’s upper stage as the telescope separated from it.”

I think “our biggest questions” may involve how to live on earth. Still, I remember seeing a video of JWST moving away from the upper stage, and being moved by the inevitability of its motion (and also the lovely gold and blue color, not quite captured in this image).

The Incredibly Cool James Webb Space Telescope 5

Webb’s Fine Guidance Sensor Provides a Serendipitous Preview “We are one week away from the release of the first science-quality images from NASA’s James Webb Space Telescope, but how does the observatory find, and lock onto its targets? Webb’s Fine Guidance Sensor (FGS) – developed by the Canadian Space Agency was designed with this particular question in mind…. The engineering test image – produced during a thermal stability test in mid-May – has some rough-around-the-edges qualities to it. It was not optimized to be a science observation, rather the data were taken to test how well the telescope could stay locked onto a target, but it does hint at the power of the telescope. It carries a few hallmarks of the views Webb has produced during its postlaunch preparations. Bright stars stand out with their six, long, sharply defined diffraction spikes – an effect due to Webb’s six-sided mirror segments. Beyond the stars – galaxies fill nearly the entire background. The result – using 72 exposures over 32 hours – is among the deepest images of the universe ever taken, according to Webb scientists.”

I like starbursts in photos myself, but this is a different order of things….

The Incredibly Cool James Webb Space Telescope 6

Telescope Alignment Evaluation Image “After completing two more mirror alignment steps, we’ve confirmed the James Webb Space Telescope’s optical performance will be able to meet or exceed the science goals the observatory was built to achieve…. 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 [18] primary mirror [hexagonal] segments have been adjusted to produce one unified image of the same star.”

The Incredibly Cool James Webb Space Telescope 7

Carina Nebula (birth): “Webb’s new view gives us a rare peek into stars in their earliest, rapid stages of formation. For an individual star, this period only lasts about 50,000 to 100,000 years.”

The Incredibly Cool James Webb Space Telescope 8

The Southern Ring nebula (death): “[T]hese are shells of dust and gas shed by dying Sun-like stars. The new details from Webb will transform our understanding of how stars evolve and influence their environments.”

The Incredibly Cool James Webb Space Telescope 9

Stephan’s Quintet: “Stephan’s Quintet, a collection of five galaxies, as seen by MIRI on the James Webb Space Telescope. The galaxies all glow in different colors, surrounded by lacy, glowing clouds of gas and dust. Four of the five are centered in the image. Three are visibly spiral galaxies, with tendrils extending out from their glowing centers. The galaxy farthest to the left appears slightly more clearly, with vibrant blue lacing surrounding the oval-shaped light of the galaxy. This is because the farthest left galaxy is not interacting with the other four; it’s actually far in the foreground from the others. The galaxies all appear against a field of sparkling stars and other, farther galaxies.”

The Incredibly Cool James Webb Space Telescope 10

Space (“it’s big”): “[This is] the deepest and sharpest infrared image of the early universe ever taken… Webb was able to capture this image in less than one day, while similar deep field images from Hubble can take multiple weeks…. The background of space is black. Thousands of galaxies appear all across the view. Their shapes and colors vary. Some are various shades of orange, others are white. Most stars appear blue, and are sometimes as large as more distant galaxies that appear next to them.

“Webb was able to capture this image in less than one day.” Big fan of long exposures, depth of field here, but holy moley! No wonder there weren’t more photos!

The Incredibly Cool James Webb Space Telescope 11

Carina Nebula (once more): “A composite image of the Cosmic Cliffs in the Carina Nebula, created with the Webb telescope’s NIRCam and MIRI instruments. Pinkish brown clouds of gas and dust dominate the foreground of the image, glittering with young stars. Behind the glowing, mountainous clouds, the sky appears navy blue, with shining stars and galaxies.”

Finally, data is important, too:

The Incredibly Cool James Webb Space Telescope 12

WASP-96 b: “The James Webb Space Telescope spotted the unambiguous signature of water, indications of haze & evidence for clouds (once thought not to exist there). This is the most detailed exoplanet spectrum to date! A spectrum is created when light is split into a rainbow of colors. When Webb observes the light of a star, filtered through the atmosphere of its planet, its spectrographs split up the light into an infrared rainbow. By analyzing that light, scientists can look for the characteristic signatures of specific elements or molecules in the spectrum. Located in the southern-sky constellation Phoenix, WASP-96 b is 1,150 light-years away. It’s a large, hot planet with a “puffy” atmosphere, orbiting very close to its Sun-like star. In fact, its temperature is greater than 1000 degrees F (537 degrees C) — significantly hotter than any planet in our own solar system!”

Very pleased that the WASP planet has water — although perhaps gin with a touch of vermouth would have been more appropriate?

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I suppose when the aliens who ended up running our quarantine whizz by the JWST, they scoff: “Mirrors! How charmingly antiquated! I stayed at a B&B on Betelgeuse IV that had one of those.” Nevertheless, I find the success of the JWST as an engineering project re-assuring; we have had no MCAS debacle; no Uber autonomous vehicle scamming; the algos seem pure. Somewhere, out there, there is a stable platform sending home images of staggering beauty, not because beauty was sought, but because it was found.

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Of course, as a final note, I should be thinking of public relations, which at NASA, despite the sad episode of the space shuttle, a bad idea badly executed, are not unknown. The New York Times, shockingly, did some actual reporting on how these particular photographs were selected, starting in 2016 (!):

In 2016, a committee of representatives from the Space Telescope Science Institute, NASA and the European and Canadian space agencies convened to start choosing Webb’s very first demo targets. They checked off boxes that vibed with the telescope’s scientific goals: a deeper-than-ever deep field, galaxies pulsing in the void like jellyfish, a star with an attendant exoplanet, star-forming regions like the Carina Nebula and more. Ultimately, this process nominated around 70 possible targets.

Once the telescope had begun operating this winter, they whittled this list down to regions of the sky it could point to within the six-week time limit — plus a few held in reserve, to tease out in the next few months as the telescope’s scientific pursuits cranked into gear.

In early June, for example, Klaus Pontoppidan, the astronomer leading this early release team, was the first human to download the new telescope’s full “deep field” view. This long, probing look at distant galaxies peers further back toward the start of time and the edge of space than any instrument of humanity has ever managed. “I was sitting there, staring at it for two hours, and then desperately, desperately wanting to share it with someone,” he said. “But I couldn’t.”

And then, finally, finally, the earliest results started trickling in through the bottleneck of Dr. Pontoppidan’s computer in early June, his being the only Webb user account granted access in this hush-hush phase of observation. From there, the team digitally combined raw frames into deeper, more polished exposures and then passed them on to image processors for color rendering.

Space exploration is never just about space. Stories matter too. And they’re often told by imagery — whether an above-the-fold print, a slickly produced livestream or a Netflix special. This tradition stretches at least as far back as the 1960s, when none other than James Webb, an early NASA administrator whose name would grace the new telescope, embraced art and visual communication as a key part of justifying the Apollo Program.

“He actually came from the State Department, where he was very well versed in ‘hearts and minds’ campaigns,” said Lois Rosson, a historian of science at the University of Southern California. While Webb was its second-ranking official, the State Department embarked on a purge of gay employees, leading to emphatic calls for NASA to rename the telescope that have gone unheeded.

So, they got me. The cold hands of a PR operation got me (and for all I know, State was Webb’s cover). On the other hand, the images are beautiful (as is the engineering), covering the hearts part. The science is worth doing, covering the minds part. Rembrandt was a businessman, after all. So was Shakespeare. Lincoln was a railroad lawyer. Ah well, nevertheless….

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