The insides of Saturn?s largest moon Titan are arranged like a slushy mix of rock and ice instead of the rigidly layered structures found in other bodies across the solar system, NASA's Cassini spacecraft has found.
Astronomers were able to determine the temperature and consistency of Titan's slushy innards by measuring the gravitational tugs registered by Cassini as it flew by the cloudy Saturn moon.
"There have been several flybys of Titan by Cassini," said study co-author David Stevenson, a professor of planetary science at the California Institute of Technology in Pasadena, Calif. "As it goes by, its path is deflected by the gravity of Titan. We use that deflection to learn about the gravity of Titan."
The gravity data reveals that the first 300 miles (500 km) down into Titan is devoid of any rock fragments, while ice and rock are mixed to various extents at greater depths. Cassini was able to record the data during four flybys of Titan between February 2006 and July 2008.
Scientists have long-known that Titan is made up of about equal parts rock and ice. Cassini's gravity data confirmed that finding and also revealed new details on the exact consistency and distribution of the interior material's makeup.
Cassini researchers described Titan's interior as "a sorbet of ice studded with rocks," in a recent NASA statement.
Researchers think Titan never heated up beyond a relatively lukewarm temperature, which explains why the moon's ice and rock have not fully divided and formed layers within Titan's interior like other bodies in the solar system.
"To avoid separating the ice and the rock, you must avoid heating the ice too much," Stevenson told SPACE.com. "This means that Titan was built rather slowly for a moon, in perhaps around a million years or so, back soon after the formation of the solar system."
Cassini built the gravity map of Titan by flying about 800 to 1,200 miles (1,300 to 1,900 km) above the moon. Scientists then used ground-based antennas with the Deep Space Network to note changes within five thousandths of a millimeter per second in the Cassini's speed as Titan's gravity perturbed the spacecraft path along its orbit.
"These results are fundamental to understanding the history of moons of the outer solar system," said Cassini project scientist Bob Pappalardo at JPL. "We can now better understand Titan's place among the range of icy satellites in our solar system."
Cassini has been studying Saturn and its rings and moons since 2004, when it arrived in orbit around the gas giant planet. The spacecraft completed its initial mission in 2008 and received and extended flight through 2017 earlier this year.
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