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Saturn’s smooth operator

Saturn's moon Telesto

The smooth surface of Saturn's moon Telesto is shown to good effect in this image captured during the Cassini spacecraft's August 27, 2009, fly-by.

Most small, rocky moons are covered in craters, having suffered millions of years of bombardment by meteoroids that happened to come along and find themselves in the wrong place at the wrong time.

Those small moons do not have volcanic, tectonic or other processes to wipe out the traces of those impacts, the craters. (By comparison, on a large world like Earth, there are lots of erosion processes—eg. wind, rain, volcanism—that have obliterated almost all traces of impact craters.)

But in the small moon stakes, Saturn’s Telesto is an exception.

Very small, only 24 kilometres long at its widest point, this moon doesn’t appear to have much in the way of craters. Rather, it seems to be covered by a layer of fine, dust-sized particles of (probably) ice, giving it a smooth appearance.

NASA’s Cassini spacecraft—which has been reconnoitering the Saturnian system since 2004—has taken several images of this mysterious moon. None of the images are very large, as Telesto is tiny and the images were taken from quite large distances.

Cassini’s closest approach to Telesto occurred in October, 2005, during which it managed to capture an image from a distance of approximately 14,500 kilometres (9,000 miles) showing detail down to 86 metres (283 feet) per pixel.

False colour view of Saturn's moon Telesto

A false colour view of Telesto reveals surface variations.

Cassini’s images reveal Telesto’s smooth nature, and show a handful of broad features such as large craters, depressions and mounds.

A special false-colour image shows subtle variations in surface texture across the face of the moon. No one’s really sure what causes the variations, but it’s probably due to small differences in the chemical composition of the ice particles, or maybe their sizes.

Another of Saturn’s moons, Pandora, has a similar dusty surface (see our earlier story on Pandora).

Telesto (pronounced teh-LESS-toh) is also a “Trojan” moon, meaning that it has an orbit that keeps it at the same distance from another body in the same orbit. In this case, Telesto always orbits 60 degrees behind the larger moon Tethys. Another moon, Calypso, orbits 60 degrees in front of Tethys. Telesto is the “leading Trojan,” Calypso is the “trailing Trojan.”

Telesto facts:

  • Discovered: in 1980 in ground-based observations by Brad Smith, Harold Reitsema, Stephen Larson and John Fountain
  • Distance from Saturn: 294,660 km (about 183,090 miles)
  • Equatorial diameter: 30 x 25 x 15 km (19 x 15.5 x 9 miles)
  • Mass: 8 x 10^17 kg

Story by Jonathan Nally, editor

Images courtesy NASA / JPL / Space Science Institute.

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