Europa, Callisto, and Io pass in front of Jupiter. Image Credit: NASA/ESA

Most of you probably know that Jupiter is the largest planet in our solar system (and if you didn’t, now you do). Its size is simply staggering: Jupiter’s volume is large enough to contain 1,300 Earth-sized planets; it contains 70% of the solar system’s planetary material; and it is so large that it has over 60 moons (67 confirmed so far). And recently, the Hubble Space Telescope captured amazing images of some of these Jovian moons.

In a rare occurrence, thee of the planet's largest moons were caught parading across the face of this gas giant. Although the planets orbit on a regular cycle, seeing three of them transiting at the same time occurs very infrequently, only once or twice a decade. In the images released today from NASA and the ESA, Europa, Callisto, and Io can be seen with their murky shadows trailing across the face of the planet. The bright bands of Jupiter's cloud formations stand out against the darkness of the surrounding sky.

As the planet is a gas giant, it is composed primarily of swirling clouds of hydrogen and helium (90% of the planet is hydrogen and the other 10% is almost entirely helium). Although most of the planet is just hydrogen and helium, Jupiter has clouds of frozen ammonia, some over 9 miles thick (15km). Ammonia gives off a rather pungent smell (similar to drying urine), so it would be rather unpleasant if you ever went for a visit. In fact, it would definitely be unpleasant, because the ammonia levels are high enough to eat away your lungs. Of course, it will eat away your skin as well, so maybe just leave the up-close encounters to unmanned space craft.

In the press release, the ESA details what can be see in the image: "The image on the left shows the Hubble observation at the beginning of the event. On the left is the moon Callisto and on the right, Io. The shadows from Callisto, Io and Europa are strung out from left to right. Europa itself cannot be seen in the image. The image on the right shows the end of the event, just over 40 minutes later. Europa has entered the frame at lower left with slower-moving Callisto above and to the right of it. Meanwhile Io — which orbits significantly closer to Jupiter and so moves much more quickly — is approaching the eastern limb of the planet."

You can see the whole event in the below video:

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