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Jupiter's Galilean Moons

Images related to my article at http://www.bellaonline.com/articles/art42279.asp, about Jupiter's four largest moons.

Jupiter's moon Europa during Voyager 2 close approach (1979-07-09). It was quite a surprise at the time to find that Europa has a crust of ice. The complex array of streaks indicate that the crust has been fractured and filled by materials from the interior. Europa has very few impact craters. Mona Evans, "Voyager 2 - the Grand Tour" www.bellaonline.c...

Water vapor venting from Jupiter’s moon, Europa | EarthSky.org - If these plumes vent from Europa’s subsurface water ocean, future scientists won’t need to drill into Europa’s icy crust to investigate the potential for life in that alien sea.

Hubble Space Telescope observations show water vapor on Jupiter's moon Europa. If this is coming through surface cracks from Europa's subsurface ocean, it could have a lot of information on what's there. This is an artist's impression showing Europa with Jupiter in the background. (Image credit: NASA, ESA, and M. Kornmesser) Mona Evans, "Jupiter's Galilean Moons" www.bellaonline.c...

Internal structure of Io, Europa, Ganymede and Callisto. © based on NASA images. More about the Galilean moons in Mona Evans, "Jupiter's Galilean Moons" www.bellaonline.c...

Jupiter’s moon Io and its tiny shadow sweep across the giant planet’s face back in 1999, as snapped by the Hubble Space Telescope. [Credit: John Spencer (Lowell Observatory) and NASA] Mona Evans, "Jupiter's Galilean Moons" www.bellaonline.c...

"Jupiter with Io and Ganymede" by Damien Peach. Winner of the Astrophotographer of the Year 2011 competition. An impressive image that compares well with those taken with large telescopes. At the lower left is Io and the larger moon is Ganymede. ©Mona Evans, "Jupiter's Galilean Moons" www.bellaonline.c...

Aurora on Jupiter's volcanic moon Io. [Credit: Galileo Project, University Of Arizona (PIRL), JPL, NASA] APOD wondered if any planet other than Earth had both volcanos and auroarae. Probably not, but Jupiter's moon Io does. Interactions between Jupiter and Io cause aurorae on both planet and moon. ©Mona Evans, "Jupiter's Galilean Moons." www.bellaonline.c...

Galileo Galilei (1564-1642). He was one of the first to use a telescope for astronomical purposes. Galileo discovered the four largest moons of Jupiter, which are now called the Galilean moons. ©Mona Evans,"Jupiter's Galilean Moons" www.bellaonline.c...

German astronomer Simon Marius (1573-1624). Four years after Galileo's account of his discovery of the Jovian moons, Marius claimed that he had discovered them before Galileo. Marius didn't get the credit, but the names in use today are those suggested by Marius. They are names of amorous conquests of Zeus (the Greek equivalent of Jupiter). ©Mona Evans,"Jupiter's Galilean Moons" www.bellaonline.c...

As befits the colossus of the Solar System, Jupiter has four of the system's largest moons: Ganymede, Callisto, Io and Europa. See them compared to other Solar System objects. ©Mona Evans,"Jupiter's Galilean Moons" www.bellaonline.c...

The 1:2:4 orbital resonance of the three inner Galilean moons. They are tidally locked, which means they keep the same face towards Jupiter as they orbit. In addition, they orbit in what's called a resonance created by a combination of Jupiter's gravity and the gravity of the moons themselves. Each time Ganymede orbits Jupiter, Europa orbits twice and Io four times. ©Mona Evans,"Jupiter's Galilean Moons" www.bellaonline.c...

Io. The most volcanically active body in the Solar System, it's about the same size as the Moon and orbits at about the same distance from Jupiter as the Moon does from Earth. Yet it has over 400 volcanoes and a “month” on Io lasts only 42 hours. This is all down to gravity. Caught between Jupiter's strong gravity and that of its companions Callisto & Ganymede, Io is mercilessly squeezed, releasing heat. ©Mona Evans,"Jupiter's Galilean Moons" www.bellaonline.c...

New species of benthoctopus found in a deep hydrothermal vent. Life has evolved there to use chemical energy rather than the energy of sunlight. Jupiter's moon Europa has a deep liquid ocean under the ice which is warmed by tidal heating. Astrobiologists think that Europa's ocean is the best place to find extraterrestrial life in the Solar System. ©Mona Evans,"Jupiter's Galilean Moons" www.bellaonline.c...

Europa. It's covered in ice and is one of the smoothest objects in the Solar System. The small number of craters shows that the surface is young, possibly only a 100 million years old. (That's young geologically.) In this picture you can see that there are also cracks and streaks. The cracking is caused by tidal heating, but we don't know exactly what the staining is. ©Mona Evans,"Jupiter's Galilean Moons" www.bellaonline.c...

Ganymede. It's bigger than Mercury, has a liquid iron core and is the only moon in the Solar System with its own magnetic field. The terrain is varied, but there are broadly two different types: heavily-cratered dark regions (evidence of great age) and brighter regions showing patterns of ridges and grooves for thousands of miles, suggesting later geological activity, but nonetheless ancient. ©Mona Evans,"Jupiter's Galilean Moons" www.bellaonline.c...

Callisto. This Jovian moon seems to be the odd one out. It's far enough away from the other three Galilean moons that it isn't part of the orbital resonance and its interior isn't warmed by tidal heating. It's also the least dense of the moons and shows the least internal layering. ©Mona Evans,"Jupiter's Galilean Moons" www.bellaonline.c...

Valhalla Crater on Callisto. Callisto is the most heavily cratered satellite in the Solar System. Its surface has apparently been primarily sculpted by impacts. Valhalla is its largest crater - it's 360 km (225 miles) across and the rings extend to 1900 km (1190 miles) from its center. (Photo: NASA) ©Mona Evans,"Jupiter's Galilean Moons" www.bellaonline.c...