Saturn's 'cool' moon Enceladus is a really hot place i
By Amanda Jermyn



If youíre looking for hot stuff on a cool moon, check out Enceladus, Saturnís sixth largest satellite. While its outer crust is extremely cold, it generates internal heat and is geologically active.

Discovered in 1789 by astronomer William Herschel, it lies in the densest part of Saturnís outermost E ring, a wide band of dust and ice particles orbiting the planet. With a diameter of only 310 miles, Enceladus is very small, only one tenth the size of Saturnís largest moon, Titan. With its clean, water ice surface, Enceladus shines brightly, reflecting almost all the sunlight that reaches it. And close beneath that icy surface there appears to be a salty, liquid water ocean.

If Enceladus receives very little heat from the distant sun and has an icy exterior, why would its interior be hot? The most likely causes are the heat generated by the decay of internal radioactive elements, as well as tidal heating. The latter occurs when Saturnís immense gravity pulls with varying strengths on either side of Enceladus, with more force exerted on the side closest to Saturn. The tidal flexing that results exerts a squeezing force, causing friction which generates heat within the moon.

While last month we explored the possibility of finding some form of life on Titan, Enceladus seems even more promising in this regard. Jupiterís moon, Europa, is also considered a prime candidate, but its water ocean lies under a very thick layer of ice. In contrast, the thin layer of ice above Enceladusí ocean would make it more accessible for exploration. More importantly, its internal warmth bodes well for the possibility of life.

From several close flybys by the Cassini spacecraft, some within about 30 miles of Enceladus, it has become clear that this moon is geologically active, with cryovolcanoes that eject ice particles, water vapor and various gases, rather than hot rock. Other objects within our solar system known to have volcanic activity include Earth, Neptuneís moon Triton, Jupiterís Io, and Saturnís Titan.

A deformed area surrounds Enceladusí south pole, showing tectonic fractures and ridges caused by internal heating. There are very few large impact craters visible in this region, indicating that the surface here is relatively young, possibly as young as 500,000 years in places, with prior volcanic activity renewing the surface and removing evidence of earlier craters. Cassini has observed active cryovolcanoes in this south polar region spewing large jets of ice particles, water vapor and other gases into space. Most of these particles fall on Enceladus as snow, some escape the moonís low gravity and reach Saturn itself, while still others, together with dust from meteoric bombardment of Enceladus, provide the main source of particles comprising Saturnís E ring. Gases found in the volcanoesí plumes include nitrogen and carbon dioxide, as well as hydrocarbons, including propane, ethane, methane and acetylene. Hydrocarbons can, in the presence of nitrogen, assemble themselves into complex structures such as amino acids which form the building blocks of life. This discovery raises the likelihood of some form of life existing in the ocean beneath the moonís surface. In fact, Enceladus is currently considered the most likely place to find extraterrestrial life in our solar system.

Join the Springfield Stars Club on Tuesday, September 25th at 7:30pm at the Springfield Science Museum for a talk by Richard Sanderson on ďA Transit of Venus Adventure at Mount Wilson Observatory.Ē Sanderson will talk about his experiences at a conference at Mount Wilson in California for this yearís Transit of Venus. The talk will include a virtual tour of the observatory and its historic instruments, as well as observations of the rare Transit of Venus through the observatoryís solar telescope and a variety of other instruments. Sanderson is curator of physical science at the Springfield Science Museum and manages the museumís Seymour Planetarium and observatory. He is also an astronomy writer who has been published in international journals such as Sky & Telescope and Astronomy. He is co-author of the 2006 book, ďIllustrated Timeline of the Universe.Ē Sanderson is a past president of the Springfield Stars Club and co-founder of the Connecticut River Valley Astronomerís Conjunction. Refreshments will be served, and the public is welcome free of charge.