Enceladus is only 500 kilometers (310 miles) in diameter, but despite its petite size, it’s one of the most scientifically compelling bodies in our solar system. It is quite similar in size to Mimas, but has a smoother, brighter surface. Enceladus reflects almost 100 percent of the sunlight that strikes it.

In 2005, Cassini’s multiple instruments discovered that this icy outpost is gushing water vapor geysers out to a distance of three times the radius of Enceladus. The icy water particles are roughly one ten-thousandth of an inch, or about the width of a human hair. The particles and gas escape the surface at jet speed at approximately 400 meters per second (800 miles per hour). The eruptions appear to be continuous, refreshing the surface and generating an enormous halo of fine ice dust around Enceladus, which supplies material to one of Saturn’s rings, the E-ring.

Several gases, including water vapor, carbon dioxide, methane, perhaps a little ammonia and either carbon monoxide or nitrogen gas make up the gaseous envelope of the plume.

Enceladus displays at least five different types of terrain. Parts of Enceladus shows craters no larger than 35 km in diameter. Other areas show regions with no craters, indicating major resurfacing events in the geologically recent past. There are fissures, plains, corrugated terrain, geysers that indicate that the interior of the moon may be liquid today, even though it should have frozen eons ago. It is possible Enceladus is heated by a tidal mechanism similar to Jupiter’s moon Io.

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“Enceladus is only a little larger than Mimas, at 500 km in diameter; but seems to have evolved differently. Rather like Ganymede, a satellite ten times its size, its surface shows large-scale cracks and flow patterns. These are thought to have been produced when the interior was melted at a later stage in its history than seems to have been the case with Mimas, requiring an internal source of heat. While Ganymede may have had enough heavy elements in its makeup for this to have been radiogenic heat, this is unlikely to have been the case for Enceladus. The alternative is tidal dissipation, as seems to be happening currently on Io and Europa, but that would require Enceladus to have had a nearer neighbour, or to have been in a different orbit, than is the case now.”

The Cambridge Photographic Guide to the Planets by F. W. Taylor [page258]

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