Next stop, Jupiter?

X-ray auroras in purple on Jupiter, as seen by the Chandra X-ray Observatory and overlaid on a simultaneous optical image from the Hubble Space Telescope. (X-ray: NASA/CXC/SwRI/R.Gladstone et al.; Optical: NASA/ESA/Hubble Heritage)

This photograph of the southern hemisphere of Jupiter was obtained by Voyager 2 on 25 June 1979, at a distance of 12 million km (8 million miles). Seen in front of the turbulent clouds of the planet is Io, the innermost of the large Galilean satellites of Jupiter. Io, which is about the size of our own Moon, is the most volcanically active planetary body known in the solar system, with continuous eruptions much larger than any that take place on the Earth. (NASA/JPL)

This is a montage of New Horizons images of Jupiter and its volcanic moon Io, taken during the spacecraft's Jupiter flyby in early 2007. (NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute/GSFC)

ebris blasted off the satellite Amalthea in high-speed collisions with interplanetary meteoroids will start with slightly inclined orbits like that of Amalthea (yellow lines), forming a slender tube around the satellite trajectory. These orbital paths are not, however, stationary in space but instead wobble about Jupiter's equator like a giant hula-hoop, keeping the same tilt off the equator but continually changing their orientations at rates that differ slightly depending on orbital size and shape. (Two orbits are shown at top.) (Jim Houghton, Galileo Imaging Team, NASA)

At first glance, Jupiter looks like it has a mild case of the measles. Five spots -- one colored white, one blue, and three black are scattered across the upper half of the planet. Closer inspection by NASA's Hubble Space Telescope reveals that these spots are actually a rare alignment of three of Jupiter's largest moons -- Io, Ganymede, and Callisto -- across the planet's face. In this image, the telltale signatures of this alignment are the shadows [the three black circles] cast by the moons. (NASA, ESA, and E. Karkoschka (University of Arizona))

Jupiter and its four planet-size moons, called the Galilean satellites, were photographed in early March by Voyager 1 and assembled into this collage. They are not to scale but are in their relative positions. (NASA)

This Voyager 2 image shows the region of Jupiter extending from the equator to the southern polar latitudes in the neighborhood of the Great Red Spot. A white oval, different from the one observed in a similar position at the time of the Voyager 1 encounter, is situated south of the Great Red Spot. (NASA)

A true-color image of Jupiter taken by the Cassini spacecraft. The Galilean moon Europa casts a shadow on the planet's cloud tops. (NASA/JPL/University of Arizona)

This close-up of swirling clouds around Jupiter's Great Red Spot was taken by Voyager 1. It was assembled from three black and white negatives. (NASA/JPL)

Image of Jupiter with NASA's Hubble Space Telescope's Planetary Camera. Eight comet impact sites are visible. (Hubble Space Telescope Comet Team and NASA)

Jupiter's composition is mainly hydrogen and helium. In contrast to planetary bodies covered with a hard surface crust (the Earth, for example), the jovian surface is gaseous-liquid, rendering the boundary between the atmosphere and the planet itself almost indistinguishable. Below the roughly 1000-kilometer-thick atmosphere, a layer of liquid hydrogen extends to a depth of 20,000 kilometers. Even deeper, it is believed that there is a layer of liquid metallic hydrogen at a pressure of 3 million bars. The planet core is believed to comprise iron-nickel alloy, rock, etc., at a temperature estimated to exceed 20,000C. (Lunar and Planetary Institute)

This Hubble picture, taken on 23 July 2009, by the Wide Field Camera 3, is the sharpest visible-light picture taken of the atmospheric debris from a comet or asteroid that collided with Jupiter on 19 July 2009. This was Hubble's first science observation following its repair and upgrade in May of that year. The size of the impactor is estimated to be as large as several football fields. (NASA, ESA, H. Hammel (SSI) and the Jupiter Impact Team)

On January 15, 2001, 17 days after it passed its closest approach to Jupiter, NASA's Cassini spacecraft looked back to see the giant planet as a thinning crescent. (NASA/JPL/University of Arizona)

This schematic cut-away view of the components of Jupiter's ring system shows the geometry of the rings in relation to Jupiter and to the small inner satellites, which are the source of the dust which forms the rings. (NASA/JPL)

When 17th-century astronomers first turned their telescopes to Jupiter, they noted a conspicuous reddish spot on the giant planet. This Great Red Spot is still present in Jupiter's atmosphere, more than 300 years later. It is now known that it is a vast storm, spinning like a cyclone. (NASA)

This storm system is Jupiter's Great Red Spot and it was captured in detail by Galileo. Using real images from three color filters, the Galileo team was able to compute what a person would see if able to float just above this ancient rotating cloud system. (The Galileo Project)

A comparison portrait of Jupiter's four Galilean moons Io, Europa, Ganymede, and Callisto, each with different characteristics. (In this image composite, Jupiter is not at the same scale as the satellites.) (NASA Planetary Photojournal)

In this Hubble telescope picture, a curtain of glowing gas is wrapped around Jupiter's north pole like a lasso. This curtain of light, called an aurora, is produced when high-energy electrons race along the planet's magnetic field and into the upper atmosphere where they excite atmospheric gases, causing them to glow. (John Clarke (University of Michigan) and NASA)

This view of the region just to the east of the Great Red Spot is seen in greatly exaggerated color. The colors do not represent the true hues seen in the Jovian atmosphere, but have been produced by special computer processing to enhance subtle variations in both color and shading. (NASA/JPL)