Let’s learn about Jupiter’s moons

Europe’s Juice mission is now on its way to get a close-up view of Jupiter’s moons

four pockmarked orbs of different sizes are in a row against a black background; the leftmost one (Io) is a splotchy orange-ish green; the second from right (Europa) is bluish-white with deep red scratches and patches; the second from right (Ganymede) is larger than the other two and silvery with white craters; the rightmost (Callisto) is slightly smaller than Ganymede and a deep blue with bright white spots

Galileo discovered these four moons of Jupiter in the 1600s. From left to right, they are Io, Europa, Ganymede and Callisto.

NASA/JPL/DLR; adapted by L. Steenblik Hwang

This month, the European Space Agency launched its Juice mission to Jupiter. The spacecraft will make some observations of the gas giant. But Juice will also get close-up views of three of Jupiter’s largest moons. These are Europa, Ganymede and Callisto. All three moons are icy worlds thought to have oceans lurking beneath their surfaces. Europa in particular is considered one of the most promising places to find alien life in the solar system.

Galileo discovered these three moons in the 17th century. He also discovered a fourth moon of Jupiter called Io. That fiery world is the most volcanically active place in the whole solar system. The discovery of those four moons was key to Galileo’s realization that Earth is not the center of the universe.

Those moons were just the beginning, though. Astronomers have found many other moons orbiting Jupiter since then. The total count is now around 90 moons. Some of those moons may have formed from a dusty disk that swirled around Jupiter long ago. Others were likely wandering space rocks that got snagged by Jupiter’s intense gravity.

Want to know more? We’ve got some stories to get you started:

Jupiter has 12 more moons than we knew about — and one is a weirdo Astronomers found a dozen previously unknown moons of Jupiter. One may be a remnant of a larger moon that was all but ground to dust. (8/20/2018) Readability: 7.8

This moon’s surface slides, just like Earth’s Plate tectonics shape the surface of Jupiter’s icy moon Europa. (9/25/2014) Readability: 7.7

There’s a real upside to knowing you could be wrong Jupiter’s moons played a major role in Galileo’s discovery that Earth is not the center of the universe. (3/30/2023) Readability: 7.4

Check out this teaser trailer for the journey of the Juice mission to Jupiter’s moons.

Explore more

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Scientists Say: Habitable Zone

Let’s learn about the hunt for alien life

Let’s learn about Jupiter

Space toilet may teach scientists how to scout for life on distant icy moons

Students help name 5 of Jupiter’s newly discovered moons

Cool jobs: Careers on ice

Jupiter’s moons could keep each other warm by raising tidal waves (Science News)

Aurora shift confirms Ganymede’s ocean (Science News)

Baby Jupiter glowed so brightly it might have desiccated its moon (Science News)


Word find

In activities from NASA’s Jet Propulsion Laboratory, see how principles of density and magnetism can help scientists study the ocean hidden beneath Europa’s surface.

Maria Temming is the Assistant Managing Editor at Science News Explores. She has bachelor's degrees in physics and English, and a master's in science writing.

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