Cassini discovers ‘underground ocean’ on Saturn’s moon Enceladus
Image data from the Cassini-Huygens mission shows that Saturn’s moon Enceladus has a subterranean ocean spread all over the celestial body. The conclusions were drawn after analyzing the so-called libration of the Saturn moon.
That writes NASA on its site. The researchers noted that the small oscillations or “libration” that the small moon has are greater than what would have been possible had the moon been made entirely of solid matter. The observed fluctuations can only be so relatively strong if the outermost layer of ice floats on a liquid layer, in this case indicating the existence of an ice-covered ocean that spans the surface of the entire moon.
Why the water layer around the stony core is not completely frozen remains a mystery, according to the researchers. For example, it could be that the tidal forces that Saturn is exerting on the moon are causing much more heat inside Enceladus than previously thought.
The spacecraft had already detected geysers of water vapor, ice particles and simple molecules in early 2005 at breaks and fissures in the ice on the moon’s surface near the south pole. That pointed to the possible existence of a water reservoir at the South Pole. Subsequent analysis of Cassini-Huygens data already suggested the existence of a lenticular body of water or sea beneath the moon’s Antarctic region. Gravity data had also already been collected that indicated a possibly larger, perhaps extensive sea. The latter appears to be the case after studying seven years of image information from the Cassini-Huygens mission.
The Cassini-Huygens spacecraft was launched on October 15, 1997 and arrived at Saturn on July 1, 2004. Since then, the probe has been sending information to Earth. The collaborative project between ESA, NASA and the Italian Space Agency is likely to run until 2017, subject to funding.
The system with which the photos are made by Cassini-Huygens is called iss, or the imaging science subsystem. The instrument uses a wide-angle camera and a small-angle camera. A small-angle camera takes pictures over a very long distance from a very small area. For comparison, a 2-euro coin is visible over a distance of 4 kilometers. A wide-angle camera, on the other hand, takes more ‘overview photos’. Both cameras take pictures with different filters and CCDs of 1024 by 1024 pixels. The system sends about 2,700 photos a month to Earth, which explains why there are so many beautiful photos of Saturn and its surroundings.
The research paper appeared online Sept. 11 in the journal Icarus.
Update 15.56: Added a short piece about the probe’s imaging system.