Enceladus, the sixth-largest moon of Saturn

 
Enceladus, the sixth-largest moon of Saturn

Image Credit: Cassini Imaging Team, SSI, JPL, ESA and NASA

Enceladus is, with a diameter of only 505 km (314 mi), the sixth-largest moon of Saturn. This oblate spheroid has a highly reflective surface devoid of impact craters and reflects almost all of the sunlight that strikes it. Because Enceladus reflects so much sunlight, the surface temperature is only -330 degrees Fahrenheit (-201degrees Celsius).

Despite the moon’s small size, it has a wide range of terrains. In addition to cratered areas, Enceladus contains smooth plains, linear cracks and ridges, fissures, and unusual crustal deformations. The smooth plains indicate a very young surface, perhaps only a few hundred million years old. The craters on Enceladus are all smaller than 21 miles (35 km) in diameter. The cracks, ridges, and other unusual features seem to indicate that the interior of the moon may still be liquid. This could be caused by internal heat as a result of tidal forces from Saturn.

Enceladus has water ice on its surface and probably sub-surface liquid water. The smooth plains were almost certainly formed by water flowing to the surface from deep inside the moon. Cryovolcanoes at the south pole shoot large jets of water ice particles into space. Some of this water falls back onto the moon as “snow”, some of it adds to Saturn’s rings, and some of it reaches Saturn.

Because of this apparent water at or near the surface, Enceladus is emerging as the most habitable spot beyond Earth in the Solar System for life as we know it.

Cassini spacecraft discovered water-rich plumes and complex hydrocarbons venting from the moon’s south polar region. The salty composition of these plumes strongly suggests that they originate from a subsurface salty ocean or subsurface caverns filled with salty water. The discovery of the plumes, along with the presence of escaping internal heat, active eruptions and very few (if any) impact craters in the south polar region, shows that Enceladus is geologically active today.

Enceladus orbits Saturn at a distance of 238,000 km from the planet’s center, between the orbits of Mimas and Tethys, keeping one face pointed toward Saturn, and requires 32.9 hours to revolve once. It orbits in the densest and narrowest part of Saturn’s diffuse E ring, the widest and outermost of Saturn’s rings. Such a wide ring is unstable, and therefore – combined with the apparent youthful appearance of the surface, and the discovery of the plumes – scientists suggest that the E-ring consists of particles vented from Enceladus’s surface.

Enceladus is perturbed in its orbit by Saturn’s gravitational field and by the large neighboring satellites Tethys and Dione. This disturbance is probably responsible for the internal heat of Enceladus.

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