The picture above right 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 mountains' 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. This image is also available in a desktop ready version

Zal Patera region of Jupiter's volcanic moon Io - Click For Desktop Ready Image

The Zal Patera region (shown right) on Io is also a 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.

Scientists 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). This image is also available in a desktop ready version