Discovery of Enceladus

On August 28 in 1789, William Herschel turn his mammoth 48-inch telescope on the planet Saturn, and identified a new moon, latter to be called Enceladus.

Just a month earlier, he had begun a systematic series of observations in order to determine the number and orbits of Saturn’s moons. His data for that year were published in the  Philosophical Transactions of the  Royal Society of London,  1 January 1790 vol. 80 pp. 427-495. You can read his paper online (if you have access) at http://rstl.royalsocietypublishing.org/content/80/427.full.pdf+html

19th and early 20th century spectroscopic observations identified water on or near the surface of the moon, but very little else wan know about it until the Voyager and Pioneer 11 flybys on the mid 1980s. These showed a bright, icy surface with a mix of moderate cratering and almost no cratering, showing the moon was still geologically active in some regions. At that time, there was no known mechanism for geologic activity on such a cold object. The Voyager I observations also lead to the hypothesis that Saturn’s E ring was actually formed of material vented by this moon, but the Voyager II observations were not good enough to confirm this.

Skip forward 20 years to 2005, and NASA’s Cassini mission’s first encounter with the moon. A lot of questions were answered in those first few flybys, and a whole lot more raised. Titan may be the largest moon, and the only one with an atmosphere, but is some planetary scientist’s books, Enceladus is the most interesting!

Enceladus (Photo credit: Wikipedia)

Cassini quickly confirmed the E ring material was ejected from some very active geysers on the younger, southern side (yep, it has a young side and an old side, like a lot of moons, and even Mars).  The southern hemisphere is lined with “tiger stripes” (the blue lines in the image at left) that are much warmer, hinting at cryovolcanism. They also appear to contain organic material, leading some scientists to speculate on the potential habitability of the moon.

Cassini is still orbiting Saturn, and still looking for more answers, though where Enceladus is concerned, every answer seems to raise at least three new questions.  http://saturn.jpl.nasa.gov/science/moons/enceladus/

If you’d like to observe Enceladus yourself, you’ll need a small telescope (48″ is nice, but 6″ will do). The Saturn’s moons javascript app from Sky&Tel will show you where to look relative to the planet.

Related articles

• Variation in water jets on Saturn moon said evidence of deep oceans (upi.com)
• Gravity controls icy moon’s spew (bbc.co.uk)
• News in Brief: Saturn’s tides drive icy moon’s plumes (sciencenews.org)
• Tides control the geysers of Enceladus (physicsworld.com)