NASA has released new images of two of Jupiter's moons -- Io and Europa -- taken by the Galileo spacecraft during encounters late last year.

The images show volcanic features on Io and the side of Europa that faces Jupiter. Pictures from the more recent, closest-every flyby of Io on February 22 are currently being transmitted to Earth and will be processed and then released in the near future.

Galileo has been orbiting Jupiter and its moons since December 1995. After its primary mission ended in December 1997, Galileo successfully completed a two-year extended mission, and it is currently embarking on another extension, called the Galileo Millennium Mission.

This picture of Jupiters volcanic moon Io combines hig-resolution black and white images taken by NASAs Galileo spacecraft on October 10, 1999, with lower resolution color images taken by Galileo on July 3, 1999 to help scientists better understand the relationships between the different surface materials and the underlying geologic structures. For example, there is red material, which is often associated with areas where lava is erupting onto the surface and is thought to be a compound of sulfur, around the margin of Monan Patera (the elongated caldera just to the lower right of center). The broad circle of bright, white material (just to the left of center) is thought to be sulfur-dioxide which is being deposited from the plume Amirani. The lengths of the shadows cast by the mountains make it possible to estimate the mountains1 heights. The southern mountain on the far right of the mosaic is approximately 8 kilometers (26,000 feet) high and the mountain to the north of it is approximately 4 kilometers (13,000 feet) high. North is to the top and the image is centered at 22.8 degrees north latitude and 109.5 degrees west longitude. The higher resolution images have a sharpness of about 500 meters (or yards) per picture element and they are illuminated from the left. These images were taken at a range of 25,000 kilometers (15,500 miles). The color images are illuminated from almost directly behind the spacecraft. The color images were taken at a distance of about 130,000 kilometers (81,000 miles) and show a resolution of 1.3 kilometers (0.8 miles) per picture element. Photo: NASA/JPL

The Zal Patera region of Jupiters volcanic moon Io is shown in this combination of high-resolution black and white images taken by NASAs Galileo spacecraft on November 25, 1999 and lower resolution color images taken by Galileo on July 3, 1999. By combining both types of images, Galileo scientists can better understand the relationships between the different surface materials and the underlying geologic structures. For example, in the center toward the top of the picture, the edge of the caldera, or volcanic crater, is marked by the black flows, and it coincides with the edge of a plateau. Also, the red material (just above and to the right of the center of the image) is typically associated with regions where lava is erupting onto the surface. Here the red material follows the base of a mountain, which may indicate that sulfurous gases are escaping along a fault associated with the formation of the mountain. Scientists can use the lengths of the shadows cast to estimate the height of the mountains. They estimate that the northernmost plateau, which bounds the western edge of Zal Patera, rises up to to approximately 2 kilometers (6,600 feet) high. The mountain to the south of the caldera has peaks up to approximately 4.6 kilometers (15,000 feet) high, while the small peak at the bottom of the picture is approximately 4.2 kilometers (14,000 feet) high. North is to the top of the image, which is centered at 33.7 degrees north latitude and 81.9 degrees west longitude. The higher resolution images have a sharpness of about 260 meters (or yards) per picture element, and they are illuminated from the left. These images were taken on November 25, 1999 at a range of 26,000 kilometers (16,000 miles). The color images are illuminated from almost directly behind the Galileo spacecraft. The resolution of the color images is 1.3 kilometers (0.8 miles) per picture element. They were taken on July 3, 1999 at a distance of about 130,000 kilometers (81,000 miles). Photo: NASA/JPL

his 12-frame mosaic provides the highest resolution view ever obtained of the side of Jupiter1s moon Europa that faces the giant planet. It was obtained by the camera onboard NASAs Galileo spacecraft on November 25, 1999 during the spacecrafts 25th orbit of Jupiter. The new images have resolutions of about 1 kilometer (0.6 miles) per picture element. Lower resolution context was provided by images acquired during earlier Galileo orbits. In the earlier images, the resolution is 7 and 13 kilometers (4 and 8 miles) per picture element, respectively. Numerous linear features in the center of the mosaic and toward the poles may have formed in response to tides strong enough to fracture Europa's icy surface. Some of these features extend for over 1,500 kilometers (900 miles). Dark er regions near the equator on the eastern (right) and western (left) limb may be vast areas of chaotic terrain. Bright white spots near the western limb are the ejecta blankets of young impact craters. North is to the top of the picture and the sun illuminates the surface from the left. The image, centered at 0 latitude and 10 longitude, covers an area approximately 2,500 by 3,000 kilometers. The finest details that can discerned in this picture are about 2 kilometers across (about 1,550 by 1,860 miles). The images were taken by Galileo's camera on November 25, 1999 when the spacecraft was 94,000 kilometers (58,000 miles) from Europa. Photo: NASA/JPL