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Juno's Daring Flyby of Europa

It seems that not a month goes by without some fantastic images being returned from an imaging instrument somewhere in space. Of all the observations planned for this year, I have been most eagerly waiting for Juno whizzing by Jupiter’s most fascinating icy moon: Europa. The last time a spacecraft came so close to Europa’s surface was over twenty years ago with Galileo, proving once more that patience is a virtue in planetary science.

The flyby finally took place on September 29th, too late for me to write about it in last month’s post (which was already hobbled up by Neptune’s breathtaking image by JWST, anyways). And we were in for a treat!

Before we analyse the image, let’s remind ourselves of the imaging instrument aboard Juno. I wrote about it in my last book: Juno was not an imaging mission to the Jovian system but a field mission to study the gas giant itself. Yet, through the design and building phase of the spacecraft, the team realised that it would be crazy to send something to orbit Jupiter and not have any instrument the image it and its neighbouring moons. So, they salvaged a somewhat basic camera from the descent stage of the Mars Curiosity rover called MARDI (11 mm focal length) and modified it for the mission (1,640 x 1,214 CCD sensor with four filters): JunoCam was born.

Since JunoCam is not a core component of the science package, its operations are restricted by limited storage and transmission bandwidth. Furthermore, with no budget for processing, citizen science initiatives were set up to allow space enthusiasts to upload and post-process the images directly. Despite these constraints, the mission images have been jaw-dropping.

Another aspect of Juno worth mentioning is that it now operates under mission extensions, allowing the mission planners to place the spacecraft on more interesting (and riskier) trajectories. In June last year, it flew by Ganymede at 1,038 km and returned beautiful shots. This time, it was Europa’s turn.

Juno’s 45th orbit of Jupiter placed it on a very tight trajectory as it passed within 352 kilometers (219 miles) of Europa’s surface (the closest ever flyby of a spacecraft was Galileo at 351 kilometers (218 miles) in January 2000) and managed to make a swath north of the equator within two hours, returning images with the highest resolution at 1 kilometer per pixel. (Galileo took an image at 6 meters per pixel in 1997).

The fact that planetary scientists got excited that a spare wide-angle camera not designed to study Jupiter’s moons took the only close-up image of Europa in over twenty years says a lot about the challenges of sending a spacecraft into the outer solar system (as well as the budgets within which these missions operate, but that’s for another post).

Now with the image itself. We can see ridges and channels crisscrossing Europa’s surface, as well as small impact craters and chaos terrains resembling icebergs indicative of subsurface pockets of warm liquids within the icy crust. The terminator shows rugged terrain and tall shadows. But it is this image below by Navaneeth Krishnan (citizen science) that I found to be truly remarkable.

(Credit: Image data: NASA/JPL-Caltech/SwRI/MSSS, Image processing by Navaneeth Krishnan)

Through enhanced processing, the image returned by Juno comes to life with beautiful colours (we still don’t know what the orange stuff is) and strong contrasts bringing out the surface features. There is so much detail in this image I have found myself studying it for long periods, although its resolution is limited by the 11mm focal length camera.

No doubt, scientists be reviewing the Juno images for years to come until NASA’s Europa Clipper and ESA’s JUICE return better-quality photos. In the meantime, note that Juno will do a flyby of fiery Io in December 2023 before ending its incredible decade-long mission.

Onwards and upwards.

(Top image credit: Image data: NASA/JPL-Caltech/SwRI/MSSS, Image processing by Björn Jónsson)


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