Evidence Grows for an Ocean Inside Saturn's Moon, Enceladus

As the Cassini space probe continues to study Saturn and its system of moons, the evidence is mounting that one of those moons, Enceladus, may have liquid water beneath its surface.  Combine this intriguing possibility with the fact that a wide array of organic compounds have also been detected on that body, and it makes Enceladus one of the most fascinating places to look for extraterrestrial life.

The special interest in this little moon began in 2005, when Cassini observed huge jets of vapor and particles coming from parallel cracks on Enceladus’ surface.  Cassini obtained a spectrogram of the material in one of the plumes by sampling the light from a star as it passed behind the plume.  To the amazement of scientists, the plume was loaded with water vapor and other chemicals necessary to produce life.   Not only that, but the cracks from which the geysers were coming, nicknamed “tiger stripes,” were actually deep valleys providing protected areas where nature could perform the delicate chemistry of forming life.  As you can imagine, Enceladus has been the object of intense scrutiny ever since.

One of the main questions that are being asked is, where’s the water coming from?  Since the initial discovery, scientists have been tossing around the interesting idea that there may be large amounts of water beneath the surface of Enceladus.  If this turns out to be true, there are further questions: just how much water, and how deep is it?  There is even the tantalizing possibility that Enceladus may have an internal ocean, which would be an even better place for life to start than the tiger stripes.

The Cassini probe is still in operation, and has continued to study Enceladus as well as the rest of Saturn’s moons.  Enceladus has not proven disappointing; in fact, the more that is learned about it, the more intriguing it becomes.  To date, Cassini has made eight flybys of Enceladus, as well as conducting observations of Saturn’s E ring, which is thought to be replenished by particles coming from Enceladus.  While interpretations of the data are still quite preliminary- and controversial, in some cases- the evidence is mounting that the moon has large amounts of water beneath its surface, possibly even the internal ocean that theorists have envisioned.

One piece of supporting evidence is the detection of sodium in the material of the E ring.  Sascha Kempf of the Max Planck Institute for Nuclear Physics in Heidelberg, Germany, has reported that Cassini’s cosmic dust detector found sodium in the E ring in concentrations of about one part in 100,000.  Jonathan Lunine of the University of Arizona in Tuscon, a Cassini researcher who was not a part of Kempf’s team, says that an ocean beneath the surface of Enceladus is the best explanation for the sodium.

“A liquid water layer or pocket in contact with the rock, which is deep below Enceladus’ surface, will acquire sodium from the rock, essentially leaching the rock,” Lunine says.  The flowing water would transport the water to the jets, which would spray it into space.  Water containing dissolved sodium would freeze into ice particles, which would be added to Saturn’s E ring.

The idea is controversial.  Roger Yelle of the University of Arizona points out that the sodium could be coming from the surface of Enceladus rather than from deep underground, and therefore would not imply the existence of an ocean.  And any interpretation of the new data is complicated by the fact that observations by Earth-based telescopes, such as the Keck Observatory at Mauna Kea, Hawaii, have not found any indication of sodium in the E ring.

But Kempf points out that such observations could only detect sodium in its gaseous state, not frozen in ice particles.  Cassini’s cosmic dust detector, on the other hand, is designed to study solid particles- and it did find sodium.

Unfortunately, Cassini’s neutral mass spectrometer did not find sodium when it flew through the plumes in March, though it did identify several organic compounds that could support life.

Other interesting information was gained when Cassini sampled Enceladus’ plumes in March and October.   Ammonia was detected in the plume material, which is interesting because ammonia is water soluble, and keeps water liquid at a lower temperature than would otherwise be possible.

Another substance found in the plume material was argon-40.  Like the sodium mentioned earlier, argon-40 would probably form in rock deep within the moon, and would stay there unless dissolved and transported to the geysers by water.  Again we have the tantalizing possibility of large quantities of water moving beneath the surface.

The evidence is inconclusive, but it’s certainly intriguing.  Enceladus, as well as the rest of Saturn’s moons, will provide us with great pictures and data for years to come.  Maybe that ocean really is there, waiting for us.  Maybe someday we’ll have submarines in there, looking for life and perhaps finding it.

Sources:

Cowen, Ron: Saturn’s Moon May Host an Ocean in Science News magazine, June 24, 2009 www.sciencenews.org/view/generic/id/44975/title/Saturn’s_moon_may_host_an_ocean

Cowen, Ron: Evidence Mounts For Liquid Interior of a Saturn Moon in Science News magazine, July 22, 2009 www.sciencenews.org/view/generic/id/45823/title/Evidence_mounts_for_liquid_interior_of_a_Saturn_moon

Website for CICLOPS (Cassini Imaging Central Laboratory for Operations) ciclops.org/view/6005/Enceladus_Rev_121_Flyby_Raw_Preview_1

Cassini: Equinox Mission at JPL website: saturn.jpl.nasa.gov/science/moons/enceladus/