The Big Picture: three Galilean moons make their way across Jupiter
It's easy for Hubble to take pictures of Jupiter or its moons, but it only gets the chance to capture the planet on cam with three visible Galilean satellites once or twice a decade. That's what makes the photo above special: it's a picture of the gas giant with three of its largest moons (and their shadows) making their way across the surface. Hubble used its Wide Field Camera 3 to take several photos of the event on January 23rd, 2015 -- the still you see above shows how the moons were positioned by the end of the 40-minute period.
You can tell the Galilean satellites apart based on the color of their surfaces, so if you're wondering, the yellow-orange one (due to an abundance of volcanic sulphur) at the top left is Io and its shadow. Callisto, the brown and biggest moon in the picture, has one of the most cratered surfaces in the solar system. Finally, the white circle at the bottom left is Europa (the same icy moon NASA wants to explore for signs of life), leaving Ganymede the only Galilean moon not invited to the party.
[Image credit: NASA, ESA, Hubble Heritage Team]
