Jupiter’s moons transiting the face of the gas giant isn’t rare. The four biggest moons orbit Jupiter anywhere between 2 and 17 days.
Seeing three of the four biggest moons transiting the planet’s face at the same time is rare. Usually, it happens once every decade or two. The last time it happened was on January 23 when Europa, Callisto and Io passed in front of our view of Jupiter at the same time.
Telescopes on the ground captured the transit as it happened. But, none can compete with the visual clarity the Hubble Space Telescope offers.
Jupiter’s three moons in these images are easy to identify thanks to their distinct colors. The icy surface of Europa appears yellowish-white. Io’s volcanic sulfur surface gives it an orange tint. Callisto’s crater-riddled surface appears brown.
The fourth biggest moon, Ganymede, wasn’t part of this party. It’s outside the Hubble’s view.
If you’re interested in checking out Jupiter’s moons for yourself, a decent pair of binoculars will do the trick.
The images were taken with Hubble’s Wide Field Camera 3 in visible light. Check out some more images of the transit below. Below the images is a time-lapse of the transit.