April 4, 2014
Discovery Of Underground Ocean Hints That Enceladus Houses Organic Life
redOrbit Staff & Wire Reports - Your Universe Online
The Cassini spacecraft and Deep Space Network have discovered evidence of a large underground ocean of liquid water on one of Saturn’s moons, suggesting that the satellite could be home to extraterrestrial microbes, according to research appearing in Friday’s edition of the journal Science.
Marc Kaufman of National Geographic reports the ocean is located between the rocky core and a layer of thick ice on Enceladus , one of Saturn’s smaller satellites. It is estimated to be about the same size as Lake Superior – relatively large for a moon with a diameter of just 310 miles (500 kilometers).
The ocean was located by Cassini, which has been exploring the moon for 10 years, and is beneath 18 to 24 miles of surface ice, the researchers explained. The apparent discovery means that Enceladus becomes the latest of Saturn’s moons that appears to be home to liquid water, joining the ranks of Titan and Europa.
“For the first time, we have used a geophysical method to determine the internal structure of Enceladus, and the data suggest that indeed there is a large, possibly regional ocean about 50 kilometers below the surface of the south pole,” Caltech planetary sciences professor and study co-author David Stevenson said in a statement Thursday. “This then provides one possible story to explain why water is gushing out of these fractures we see at the south pole.”
Stevenson and his colleagues, including lead author Luciano Iess of Sapienza University of Rome, collected extremely precise measurements of Cassini’s trajectory by tracking its microwave signal carrier with the Deep Space Network during three flybys of the moon from April 2010 through May 2012. By monitoring the effect that Enceladus had on the probe’s signal frequency, the study authors were able to learn about the moon’s gravitational field and the distribution of its mass.
They discovered a negative mass anomaly at Enceladus's south pole, which indicates that there is less mass in the location than would be expected in the case of a uniform spherical body. Since the investigators knew there was a depression in the surface of the south pole, they expected to find the negative mass anomaly, but they were surprised that it was smaller than would have been predicted by the depression alone.
This type of compensation for mass is not uncommon on different planetary bodies, but typically the lack of material at the surface is made up for by the presence of deeper, denser material. In the case of Enceladus, the absence of surface material is compensated at depth by the presence of material that is denser than ice, and according to Stevenson, the “only sensible candidate for that material is water.”
“By analyzing the spacecraft’s motion in this way, and taking into account the topography of the moon we see with Cassini’s cameras, we are given a window into the internal structure of Enceladus,” said Iess. “The perturbations in the spacecraft’s motion can be most simply explained by the moon having an asymmetric internal structure, such that an ice shell overlies liquid water at a depth of around 30–40 km in the southern hemisphere.”
While the discovery of the ocean itself is interesting, experts are more excited by the fact that the moon’s wet environment could be favorable enough to house microbial life. The study authors believe water vapor found in Enceladus’ geysers originates from the subsurface ocean, and that organic material detected in that plume increased the likelihood that life once existed (or still exists) on the diminutive moon.
“Material from Enceladus’ south polar jets contains salty water and organic molecules, the basic chemical ingredients for life,” added Linda Spilker, Cassini project scientist at NASA’s Jet Propulsion Laboratory (JPL) in Pasadena, California. “Their discovery expanded our view of the 'habitable zone' within our solar system and in planetary systems of other stars. This new validation that an ocean of water underlies the jets furthers understanding about this intriguing environment.”