Callisto is the one of the Galilean moons of Jupiter, the second largest. Its surface is old, showing the highest coverage by impact craters of any large body in the Solar System, but it has no volcanoes or large mountains. Callisto’s surface is one large ice-field, littered with cracksand craters from billions of years of collisions. This picture was taken in 2001 by the Galileo spacecraft.

Image Credit: NASA


idamoonThis color mosaic shows the asteroid Ida and its moon Dactyl. The images use to assemble this picture were taken by the camera system on the Galileo spacecraft as it was passing through the Asteroid Belt in 1993. Ida is about 52 km in length and, as you can see, is irregularly shaped. The image shows many craters, including quite a few degraded ones, indicating Ida’s surface is older than previously thought.

Dactyl was discovered in the series of images Galileo recorded over an observation period of 5.5 hours during the 1993 flyby of Ida. Dactyl’s longest dimension is about 1.6 km.

Image Credit: NASA


The asteroid Ida orbits the Sun between the orbits of Mars and Jupiter. It takes about 4.8 years to complete an orbit. Ida has a moon named Dactyl, official designation (243) Ida I Dactyl, discovered in images taken by the Galileo spacecraft during its flyby in 1993. These images provided the first direct confirmation of an asteroid moon. Dactyl is heavily cratered, like Ida, and consists of similar materials, suggesting they are fragments of the same parent body. Ida is the dot on the right side of the image above. The image on the left is our best closeup of Dactyl to date. Dactyl is about 1.6 x 1.4 x 1.2 km across.

Image Credits: NASA


Jupiter has (at last count) 79 moons. The four Galilean moons make up over 99.9% of the mass of all of the planet’s satellites. The next largest moon Amalthea was discovered in 1892. It’s irregularly shaped, 250 × 146 × 128 km, and not much was know about until the Voyager 1 and 2 flyby of Jupiter in 1979 and the Gailieo order mission which did a close pass by the moon in 2002.

Image Credit: NASA

Jupiter’s Magnetosphere

This visualization shows a simplified model of Jupiter’s magnetosphere, designed to illustrate the scale,  basic features of the structure, and impacts of the magnetic axis (cyan arrow) offset from the planets axis of rotation (blue arrow). It was derived by taking a fresh look at data from the Galileo mission which ended in 2003.

Video Credit: NASA


This video shows a map of Ganymede based on images from the Galileo orbiter. The U. S. Geological Survey has classified the surface of Ganymede into various types of terrain. The regions shown in brown are those that are heavily cratered and much older than the light shaded regions that are smoother with few craters. The lighter shaded regions were likely formed by flooding of the surface with water coming from faults or cryo-volcanos that has occurred over billions of years. Tectonic processes may be at work with some crustal ice sheets being forced downward by the emergence of newer icy material. The best models of Ganymede from the Galileo data suggest a deep ocean under a thick ice crust.

Video Credit: NASA / USGS

Io’s True Colors

io_truecolorJupiter’s moon Io is one of the weirdest in the Solar System. It’s bright yellow, and this picture is an attempt to show how Io would appear to the average human eye. Io’s colors derive from sulfur and molten silicate rock. The moon’s is constantly being refreshed by a system of active volcanoes. Tides caused by Jupiter’s gravity stretch Io, and the resulting friction greatly heats Io’s interior, causing molten rock to explode through the surface. Io’s volcanoes are so active that they are effectively turning the whole moon inside out. Some of Io’s volcanic lava is so hot it glows in the dark.

Image Credit: NASA

Planetary Rings

RingsThese belong to Jupiter, not Saturn. The ring system of Jupiter was imaged by the Galileo spacecraft in 1996. This image of the west ansa (the edge of a ring system) of Jupiter’s main ring has a resolution of 24 km per pixel. Plotting the brightness of ring from the inner-most edge of the image to the outer-most through the thickest part of the ring, shows the “dips” in brightness caused by perturbations from satellites. Two small satellites, Adrastea and Metis, which are not seen in this image, orbit through the outer portion of the ansa much like the small moons that shepherd Saturn’s rings.

Image Credit: NASA