On July 12, 2022, first JWST images and spectra releasedAnd they were absolutely spectacular. Galaxies, stars, nebulae and even observations of the atmosphere of a distant exoplanet – all amazing and just a hint of what the space observatory will do in the coming years.
But even before those images were released, astronomers and engineers were busy running JWST through a series of tests, including looking at how well it could track objects. JWST is in an Earth-like orbit around the Sun, so deep space objects only appear to move about 1° per day (360° around the Sun in a year divided by 365 days per year). That is not too difficult.
But solar system objects move much faster. For one, they orbit the Sun, so they move against background stars, plus the Earth, and thus JWST, also orbit faster than the outer planets, so it adds to their motion.*. JWST needs to be able to track these targets if astronomers can hope to observe them.
To test its capabilities, they ordered JWST to target the King of the Planets, Jupiter. And why not: It’s big and bright, so exposures can be short, and it moves faster than the other outer planets, so if JWST can track it, then we’re good to go.
These engineering test images were not released with the others, but were made public in the data archive. Many different people pounced on them, using their abilities to create images from the data. And oh my, the results. Oh, me.
First, here is the “official” image taken by the Near Infrared Camera, or NIRCAMat JWST.
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This was taken with a 2.12-micron filter, which selects light with wavelengths about 2-3 times longer than what the human eye can see. This particular filter lets through a very narrow range of wavelengths, which is advantageous when looking at something as bright as Jupiter; it cuts out a lot of light that would otherwise overwhelm the camera. Cold molecular hydrogen: two bonded hydrogen atoms, called Htwo — emits light at this wavelength, so the filter is useful for observing star-forming regions in galaxies.
That image has been cleaned up considerably. The raw images were not observed to make pretty pictures, but instead helped to get the telescope going. So for example you can see black spots on Jupiter which are pixels on the detector that are not calibrated correctly. The bright object on the left is Europa, Jupiter’s moon, which was so bright that it saturated the detectors, flooding it so strongly that the central region turns black; think of it a bit like trying to fill a bucket with a fire hose, with most of the water splashing out. That’s not an exact analogy, but close enough.
You can see a lot of familiar structures in Jupiter’s cloud tops, including the wide fringes. However, this image is in the infrared, then things look different. The Great Red Spot, for example, emits a lot of light at 2.12 microns, so it appears very bright, as do several of the broad bands. The poles, which normally appear dark in visible light, are bright here. These differences between what we see in visible and infrared light tell planetary scientists about conditions in Jupiter’s clouds, helping them understand the complex chemistry and behavior of these structures.
So: the image is functional and quite good. But then some people who love to play with images from space telescopes got their hands on the data and yeGADS.
that image was processed by ian reganwho has a long history of working with space-based data. He cleaned the data and applied various techniques to bring out the details. Much more structure can be seen in the planet’s atmosphere, as well as Europa’s shadow just to the left of the Great Red Spot. Handsome.
judy schmidtwhose name may be familiar to regular readers because I have written about his work many times beforealso processed the data, but did something different, creating a color image from three different filters, and the results are simply amazing:
My God. The 2.12-micron filter image is shown here as blue, and it used a combination of two filters: a 3.22-micron filter that lets in light of a wide range of wavelengths, and a 3-micron filter, 23 microns with a much narrower bandpass, to create the red. layer.
In addition to adding color, his images have the contrast stretched upwards, revealing two very noticeable features.
The first is the ring of Jupiter! You can see it as a thin elliptical arc to the right and left of the planet itself. Although not as glorious and flashy as Saturn’s magnificent rings, Jupiter’s main ring was discovered in 1979. when Voyager flew over the giant planet. Faint rings were found later. The main ring is mostly dust, unlike Saturn’s, which is nearly pure water ice. On Jupiter’s right side you can also see two bright spots in the ring; those are tiny moons metis Y adrastrea, whose gravity helps keep dust particles trapped in the narrow ring, and may also be a source of dust. The faint glow over Europe on the left is the moon Thebesby the way.
Seeing the ring was a surprise, but not nearly as big as the bright arc to the right of Jupiter, just outside the curved edge of the planet itself!
It is not clear what that is. It could be an artifact of the camera looking at such a bright planet, like an internal reflection. But if so, I’d expect it to appear as a solid disk, not a narrow arc. Many planetary scientists think that it may instead be real: a mist of particles suspended high above the cloud tops. Sunlight enters slightly from the left in this image, so it is possible that it is illuminating a thin layer in the upper atmosphere. If so, this is another free bonus that JWST has given to scientists, a gift that no one expected.
And this hints at glories to come. JWST has a full program, observing objects from the inner solar system to literally the edge of the observable Universe. And it’s just beginning.
Just wait. Much more is coming. Much.
* JWST cannot look at Venus or Mercury, which are too close to the Sun in the sky. The observatory is designed to keep out sunlight to avoid heating up the instruments and mirrors, which operate at temperatures close to absolute zero. Because of this, it can only observe solar system objects outside of Earth’s orbit.
