Hubble Captures Jupiter Triple-Moon Conjunction

Posted on February 6, 2015

Hubble image of Jupiter triple-moon conjunction

The Hubble Space Telescope has captured a rare triple-moon conjunction on the face of Jupiter. The three moons involved are Europa, Callisto, and Io. The event took place on January 24, 2015. The image was captured with Hubble's Wide Field Camera 3.

The three moons have orbits around Jupiter that range from 2 days to 17 days. Io has the fastest orbit around Jupiter of 42 hours. Europa completes its orbit in 85 hours and Callisto takes 17 days. NASA says seeing three moons transiting the face of Jupiter at the same time is a rare occurrence. It happens just once or twice each decade.

The three moons are named Galilean moons after Italian astronomer and scientist Galileo Galilei who discovered the moons using a telescope in 1610. There is also a fourth Galilean moon, Ganymede, which is not pictured in above image. The four moons are the largest of Jupiter's satellites.

You can see a larger image of the triple-moon conjunction here. Europa can be seen entering near the end of the event at the bottom right.

The last Jupiter image released by Hubble was October 28, 2014 when it released this image of the planet appearing to have a giant eye. The "eye" was caused by a combination of Jupiter's Great Red Spot and Ganymede's shadow.

Photo: NASA, ESA, Hubble Heritage Team