Ganymede Casts a Long Shadow Across the Surface of Jupiter

NASA’s Juno spacecraft captured this view of Jupiter during the mission’s 40th close pass by the giant planet on Feb. 25, 2022. The large, dark shadow on the left side of the image was cast by Jupiter’s moon Ganymede. Image data: NASA/JPL-Caltech/SwRI/MSSS Image processing by Thomas Thomopoulos

What is that large dark smudge on Jupiter’s side? It may remind you of a certain scene from the sci-fi film “2010: The Year We Make Contact,” where a growing black spot appears in Jupiter’s atmosphere.

But this is a real photo, and the dark spot is just an elongated shadow of Ganymede, Jupiter’s largest moon. Just like when Earth’s Moon crosses between our planet and the Sun creating an eclipse for lucky Earthlings, when Jupiter’s moons cross between the gas giant and the Sun, they create shadows too.  

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Jupiter and Ganymede are Connected by Magnetic Fields

Credit: SwRI

On July 5th, 2016, NASA’s Juno spacecraft arrived at Jupiter and began its four-year mission (which has since been extended to 2025) to study the gas giant’s atmosphere, composition, magnetosphere, and gravitational environment. Juno is the first dedicated mission to study Jupiter since the Galileo probe studied the system between 1995 and 2003. The images and data it has sent back to Earth have revealed much about Jupiter’s atmosphere, aurorae, polar storms, internal structure, and moons.

In addition, the Juno mission has allowed astronomers to learn more about how magnetic interaction between some of Jupiter’s moons and its atmosphere leads the gas giant to experience aurorae around its northern and southern poles. After analyzing data from Juno’s payload, a team of researchers from the Southwest Research Institute (SwRI) observed how streams of electrons from Ganymede (Jupiter’s largest moon) leave an “auroral footprint” in Jupiter’s atmosphere.

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This was Juno’s View on its 37th Flight Past Jupiter

Jupiter, as seen from Juno during its 37th pass over Jupiter. Credit: NASA/JPL-Caltech/SwRI/MSSS/Kevin M. Gill

As originally planned, Juno’s 37th close pass by Jupiter – called Perijove 37 – would have been its last. Per the original mission outline, the Juno spacecraft would have been programed to plunge into Jupiter on Perijove 37 as a mission-ending self-sacrifice. Destroying Juno would protect the Jovian moons — especially Europa — from potential future contamination by an unpowered spacecraft wandering adrift through the Jupiter system. As careful as NASA is about taking precautions to limit the amount of Earth-sourced biological material carried by robotic spacecraft, it’s incredibly difficult to ensure that no microbes might have tagged along.

But, back to Juno: as it stands now, the Juno mission is just getting started. With a mission extension granted earlier this year, Juno will continue to operate until at least 2025, with 42 extra orbits added to the mission.

And thank goodness, because the images from Perijove 37 are pretty stunning. The new mission plan put Juno on a relatively close pass to image Jupiter itself, as well as a great view of Jupiter’s moon Europa, see below.

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Here’s What it Would Be Like to Fly Low Over Jupiter’s Cloudtops

Jupiter, via Juno. Picture shows lower elevation and uses standard perspective projection. Credit: NASA/JPL-Caltech/SwRI/MSSS/Kevin M. Gill

During Juno’s extended mission, every orbit is like a new adventure. Each orbit is a little different, and NASA says the natural evolution of Juno’s orbit around Jupiter provides a wealth of new science opportunities.

But for most of us, what we look forward to on every perijove – the point in each orbit where the Juno spacecraft comes closest to the gas giant – are the incredible images taken by the camera on board, JunoCam. As Juno’s “eyes,” the camera provides a unique vantage point no other spacecraft has been able to give us.

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Ganymede in Infrared Taken During Juno’s Most Recent Flyby

Infrared view of Jupiter’s icy moon Ganymede was obtained by the Jovian Infrared Auroral Mapper (JIRAM) instrument aboard NASA’s Juno spacecraft Image Credit: NASA/JPL-Caltech/SwRI/ASI/INAF/JIRAM

On July 20th, 2021, NASA’s Juno spacecraft conducted a flyby of Jupiter’s (and the Solar System’s) largest moon, Ganymede. This close pass was performed as part of the orbiter’s thirty-fourth orbit of the gas giant (Perijove 34), which saw the probe come within 50,109 km (31,136 mi) of the moon’s surface. The mission team took this opportunity to capture images of Ganymede’s using Juno’s Jovian Infrared Auroral Mapper (JIRAM).

These were combined with images acquired during two previous flybys to create a new infrared map of Ganymede’s surface, which was released in honor of the mission’s tenth anniversary (which launched from Earth on Aug. 5th, 2011). This map and the JIRAM instrument could provide new information on Ganymede’s icy shell and the composition of its interior ocean, which could shed led on whether or not it could support life.

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Juno Captured This Image of Earth on its Way Out to Jupiter Back in 2013

Earth as seen by the JUNO spacecraft in 2013. Credit: NASA/JPL-Caltech/SwRI/MSSS/Kevin M. Gill.

Since the Juno spacecraft has been in orbit around Jupiter for nearly five years — since July 4, 2016 — you may have forgotten about that time back in 2013 Juno flew past Earth. The spacecraft needed a little extra boost to reach Jupiter, so it used Earth for a gravity assist. Image editor Kevin Gill reminded us of that flyby with some stunning newly processed images of Earth, taken by the JunoCam, the “citizen science” camera on board. Pale blue dot indeed!

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Finally! New Pictures of Ganymede, Thanks to Juno

Ganymede seen by JunoCam. The image is derived from a raw PJ34 JunoCam image, decompanded and stretched in a linear way in order to remove dark and to improve contrast moderately. Credit : NASA / JPL / SwRI / MSSS / Gerald Eichstädt.

Well, hello there old friend! This week the Juno mission to the Jupiter system made the first close flyby of Jupiter’s giant moon Ganymede, and as you might guess, the images are spectacular. This is the first time we’ve seen a close-up view of the Solar System’s largest moon since the Galileo mission 20 years ago. Voyager gave us the first views of Ganymede 40 years ago.  Now, planetary scientists will be able observe any changes in Ganymede’s surface over time.

But first, the image editing gurus back on Earth are having a go at the raw images sent back by Juno. Our lead image comes from Gerald Eichstädt, who worked his magic to bring out the details of Ganymede, and it’s a stunner.

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Stare Straight Down Into a Giant Storm on Jupiter

A view from the Juno spacecraft of a giant storm on Jupiter. Credit: NASA/JPL-Caltech/SwRI/MSSS/Kevin M. Gill

A new batch of images recently arrived at Earth from JunoCam, the visible light camera on board the Juno spacecraft at Jupiter. The camera has provided stunning views of the gas giant world since the spacecraft’s arrival in 2016. Citizen scientists and imaging enthusiasts act as the camera’s virtual imaging team, participating in key steps of the process by making suggestions of areas on Jupiter to take pictures and doing the image editing work.

This lead image, edited by Kevin Gill, is another stunner: a look straight down into a giant storm.

And we like Kevin’s attitude about this whole process:

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With its New Extension, Juno is Going to be Visiting Jupiter’s Moons

Citizen scientist Kevin M. Gill created this image using data from the spacecraft's JunoCam imager. Credits: NASA/JPL-Caltech

The Juno mission to Jupiter has been extended to September 2025 – or however long the spacecraft can keep operating around Jupiter.

While Juno has so far focused its attention on the giant planet alone, the mission extension will include observations of Jupiter’s rings and large moons, with targeted observations and close flybys planned of the moons Ganymede, Europa, and Io.

This will be the first close flybys of these moons since the Galileo mission in 1995-2003.

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