NASA’s Cassini spacecraft performed a daring flyby of Saturn’s moon Enceladus on Wednesday, speeding at 15 kilometres per second through icy Old-Faithful-like geysers erupting from giant fractures in the moon’s cracked shell, and capturing the highest resolution views yet of the north polar region.

This three-image mosaic is the highest resolution view yet of Enceladus’ north polar region. The image looks south over cratered and fractured terrain from high above the north pole. Image: NASA/JPL/Space Science Institute.

The new data provide a much more detailed look at the fractures from which the geysers emanate and reveal significant differences between the moon’s north and south polar regions. The north polar region is found to be much older, pitted with craters of varying sizes and degradation and showing alteration by tectonic activity and possibly past heating from below. Although similar conclusions were reached from the Voyager images, the new data give a significantly improved comparison of the geologic history of the north and south poles.

The new images also show a variety of different crater morphologies, some with raised floors and others with smaller craters within, and many showing evidence of having been sliced by small parallel cracks. Two prominent overlapping craters, Ali Baba and Aladdin, are among the largest craters known on Enceladus. Also visible in the image are patches of much younger terrain, labelled Samarkand Sulci and “leading hemisphere terrain”. Samarkand Sulci slices through some prominent craters images by Voyager and it was originally thought that the parts of the craters that extended into the terrain were completely destroyed. However, the new images from Cassini show that some remnants of the crater rims have survived, providing clearer insight into how tectonic processes modify older terrains and how the geological history of these different terrains has unfolded over time.

"These new images are showing us in great detail how the moon's north pole differs from the south, an important comparison for working out the moon's obviously complex geological history," says Carolyn Porco, Cassini imaging team leader of the Space Science Institute at Boulder, "And the success of yesterday's daring and very low-altitude flyby means this coming summer's very close encounter, when we get exquisitely detailed images of the surface sources of Enceladus' south polar jets, should be an exciting 'next big step' in understanding just how the jets are powered."

Close-up view of Enceladus, showing the younger, fractured terrain cutting through older craters. Image: NASA/JPL/Space Science Institute.