Evolution of Infrared Space Telescopes

Comparing Incredible Webb Space Telescope Images With Other Infrared Observatories

The evolution of infrared astronomy, from Spitzer to WISE to JWST. Credit: Andras Gaspar

the published images speak James Webb Space Telescope (JWST) last week aren’t officially “first light” images of the new telescope, but somehow it looks like they are. These breathtaking views provide the first indications of JWST’s power and how much infrared astronomy is about to get better.

The images were released after the lengthy process of fully focusing the telescope’s mirror segments was completed. Engineers say JWST’s optical performance is “better than even the most optimistic predictions,” and astronomers are wild with excitement.

” He does not have broke the laws of physics, but stands at the best of possibilities thanks to the extraordinary efforts of several decades,” said Mark McCaughrean, Senior Adviser for Science and Exploration at the European Space Agency and member of the JWST Science Working Group, on Twitter.

In their excitement, astronomers began posting comparison images – from previous telescopes at the JWST in the same field of view – showing the progress of the improved resolution.

Astronomer Andras Gaspar, who works with JWST’s mid-infrared instrument MIRI, compiled images from the Wide Infrared Survey Explorer (WISE) telescope to JWST’s image of the same field of view, the Large Magellanic Cloud, a small satellite galaxy of the[{” attribute=””>Milky Way.

How awesome is JWST/MIRI? Well, let’s compare the latest press release image to that of the WISE all-sky survey at 4.6 microns. This is the closest wavelength image I could find. Spitzer IRAC would have been better (slightly higher resolution and similar wavelength). https://t.co/EXqP57sULt

Then he realized Spitzer also has taken an image of the LMC, and then created the comparison of the three telescopes, seen in our lead image.

“To be fair, WISE with its 40 cm diameter telescope was only half the size of Spitzer’s [85cm primary] but both are tiny compared to JWST [6.5 meter primary]” Gaspar said on Twitter. “That’s what you get with a wide open!” Resolution and Sensitivity. And MIRI gives a medium IR! HST [Hubble Space Telescope}] can’t get that wavelength.

And there’s more :

Since #JWST’s MIRI is getting a lot of love before and after, I thought I’d do the same for the thin guidance sensor: here’s one of its two fields in the Large Magellanic Cloud, as before imaged in the near infrared by @ eso’s VISTA survey telescope. 1/ https://t.co/G4yfhPWTqQ

Astronomers and engineers actually seem amazed at the quality of JWST’s resolution. You may find this surprising. I mean, don’t they do ground tests to find out the capabilities of telescopes before launch? Yes, but ground tests don’t always tell the whole story, as Marshall Perrin, assistant project scientist for Webb at the Space Telescope Science Institute explained on Twitter.

“Yes, we had tested the whole optical train in cryo in Houston – but that didn’t really tell us the ultimate performance,” he wrote. ” Not entirely. In many ways, the ground test environment was harsh and different from space.

Perrin explains how gravity plays a role, as JWST’s mirrors are designed to have a certain zero-g shape, but in all ground tests they were inevitably distorted by gravity, requiring digital models to compensate.

Then there’s no way to test on the ground how the telescope might perform in zero-g, in terms of stability or whether there will be spacecraft vibrations. And while the ground test in the thermal vacuum chamber at Johnson Space Center could match the temperatures JWST would experience in space, Perrin said some effects in the test chamber induced optical instabilities.

“A performance prediction should not just be a wave or a wish, it should be based on quantitative numerical models and budgets, including the assessment of risks and uncertainties”, he wrote.

So, while predictions are useful, there are always uncertainties. For now, let’s savor the joy and wonder that JWST already provides.

The first official images should arrive in July.

Originally published on Universe today.

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