Jupiter's moons in focus

Europa's icy crust may conceal an ocean

By BBC News Online science editor Dr David Whitehouse

This mosaic provides the best view ever obtained of the side of Jupiter's moon Europa that faces the giant planet.

Tides may crack the ice

The 12 images of the ice-encrusted surface were taken by the Galileo spacecraft last November during its 25th orbit of Jupiter. Details as small as one kilometre (0.6 miles) can be seen.

Astronomers believe that beneath the ice-crust lies a liquid water ocean which some think may be a good place to look for alien life.

Linear features visible in the centre of the mosaic and toward the poles may have formed in response to tides strong enough to fracture the moon's icy surface.

Some of these features extend for over 1,500 km (900 miles). Darker regions near the equator on the eastern (right) and western (left) limb may be vast areas of chaotic, broken terrain. Bright white spots near the western limb are the ejecta blankets of young impact craters.

Io is the most volcanic world in the Solar System

High-resolution images of Jupiter's volcanic moon Io have also just been released by Galileo mission scientists. They show the relationships between the different surface materials and the underlying geologic structures on Io.

The red material, seen around the margin of an erupting volcano called Monan Patera, is thought to be a compound of sulphur. A broad circle of bright, white material seen in the image is thought to be sulphur-dioxide being deposited from the plume called Amirani.

Sulphurous chemicals spill on to the surface

The lengths of the shadows cast by the mountains make it possible to estimate the mountains' heights - between 4,000 and 8,000 metres (13,000 to 26,000ft) high.

Another Io image shows the Zal Patera region. The edge of this volcanic crater is marked by black flows, coinciding with the edge of a plateau. In this image, the red material follows the base of a mountain, which may indicate that sulphurous gases are escaping along a fault associated with the formation of the mountain.

Io is the most volcanic world in the Solar System.