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Hubble captures rare triple transit of Jupiter’s moons

New images capture a rare occurrence as three of Jupiter’s largest moons – Europa, Callisto and Io – parade simultaneously across the giant planet’s banded face.

The images were taken with NASA/ESA Hubble Space Telescope’s Wide Field Camera 3 on January 23, 2015.

Hubble captures these moons in great clarity they can also be seen here on Earth with a small telescope or even a decent pair of binoculars.

The images 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 Europa, which cannot be seen in the image, Callisto, and Io are strung out from left to right. The images on the right shows the end of the event, approximately 42 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 appears to move much more quickly — is approaching the eastern limb of the planet. Whilst Callisto’s shadow seems hardly to have moved Io’s has set over the planet’s eastern edge and Europa’s has risen further in the west. Image credit: NASA/ESA

The images 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 Europa, which cannot be seen in the image, Callisto, and Io are strung out from left to right. The images on the right shows the end of the event, approximately 42 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 appears to move much more quickly — is approaching the eastern limb of the planet. Whilst Callisto’s shadow seems hardly to have moved Io’s has set over the planet’s eastern edge and Europa’s has risen further in the west. Image via NASA/ESA

Jupiter’s four largest moons are Io, Europa, Ganymede, and Callisto, known as the Galiliean moons, after the 17th century scientist Galileo Galilei, who discovered them. Their complete orbits around Jupiter range from two to 17 days in duration. The moons can commonly be seen transiting the face of Jupiter and casting shadows onto its layers of cloud. But seeing three of them transiting the face of Jupiter at the same time is rare, occurring only once or twice a decade.

Missing from sequence of images is the Galilean moon Ganymede which was outside Hubble’s field of view.

The moons of Jupiter have very distinctive colors. The smooth icy surface of Europa is yellow-white, the volcanic sulphur surface of Io is orange and the surface of Callisto, which is one of the oldest and most cratered surfaces known in the solar system, is a brownish color.

The event is shown from start to finish in the video below.

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Bottom line: New images taken by the NASA/ESA Hubble Space Telescope on January 23, 2015 capture a rare occurrence as three of Jupiter’s largest moons – Europa, Callisto and Io – parade across the giant planet’s banded face.

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Eleanor Imster

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