New information from the Cassini spacecraft has lead scientists to come to a surprising conclusion about Saturn’s famous moon Titan. It has been documented for awhile that this little moon contains lakes which are made of methane and ammonia, but now, fro new Cassini observations, it is thought that Titan has a subterranean ocean, covered by a layer of ice and a thick, organic atmosphere. This is because of a tidal flux that is now observed to be much greater than would be expected from a “rock tide”. Because of the gravitational pull of Saturn during the satellite’s orbit, a solid tide, made of only rock, would be expected to be about 3 feet, or one meter in height. What Cassini found, though, is a tidal flux of 30 feet (10 meters), which can only suggest that Titan is not completely made of solid rock. Just as a point of comparison, the tides on Earth which result from the gravitational pull of our moon on the oceans can get to be about 2 feet, while the pull from the sun and the moon on the Earth’s crust can cause bulging “solid tides” of about 20 inches.
Luciano Iess, the lead author of the paper published in Science yesterday and a Cassini team member from Sapienza University in Rome, Italy, stated that “Cassini’s detection of large tides on Titan leads to the almost inescapable conclusion that there is a hidden ocean at depth. The search for water is an important goal in solar system exploration, and now we’ve spotted another place where it is abundant.”
What Cassini actually measured was the squeeze and pull effect of Saturn’s gravity on Titan. As the spacecraft made a few fly-by’s, scientists were able to measure the amount of elongation that the moon experienced at different parts of its orbit. Because Titan is not completely spherical to begin with, these changes in its shape were fairly detectable. As Titan gets closer in it’s orbit to Saturn, it becomes more elongated, and and as it gets farther from Saturn it becomes nearly round.
Sami Asmar, a Cassini team member at NASA’s Jet Propulsion Laboratory in Pasadena, California, stated ”We were making ultrasensitive measurements, and thankfully Cassini and the DSN were able to maintain a very stable link. The tides on Titan pulled up by Saturn aren’t huge compared to the pull the biggest planet, Jupiter, has on some of its moons. But, short of being able to drill on Titan’s surface, the gravity measurements provide the best data we have of Titan’s internal structure.”
This does not mean that Titan has life on it, however. It is now believed by scientists that life is most likely to arise when liquid water is in contact with rock, and these measurement do not lead to any conclusions about whether the bottom of Titan’s oceans are made of rock or ice. Jonathan Lunine, a Cassini team member at Cornell University, Ithaca, N.Y, explains why these findings are important: ”The presence of a liquid water layer in Titan is important because we want to understand how methane is stored in Titan’s interior and how it may outgas to the surface. This is important because everything that is unique about Titan derives from the presence of abundant methane, yet the methane in the atmosphere is unstable and will be destroyed on geologically short timescales.” It may help solve the mystery of methane replenishment on Titan.
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