Main Content
The Cassini probe zooms past a cutaway section of Saturn's moon Titan in an artist's rendering.
Image courtesy NASA/JPL
Published March 11, 2010
Saturn's largest moon, Titan, is perhaps best know for its unique, hazy atmosphere and lakes of liquid methane.
But a new look at Titan's insides reveals even more oddities: Beneath the brittle crust of ice lies a layer of slush. Deeper still is an underground ocean over a solid core of rock and ice.
This new picture is based on measurements of Titan's gravity field. The measurements were made by clocking the speed of the NASA-ESA Cassini orbiter with extreme precision—gaguing how many five-thousands of a millimeter the craft traveled per second.
"The ripples of Titan's gravity gently push and pull the spacecraft. By studying the velocity changes we can calculate the gravity," explained study leader Luciano Iess, of Sapienza University of Rome.
Subtle differences in Titan's pull on Cassini suggest that the materials inside the moon are a mix of ice and rock with no clearly defined rocky layers.
Titan's Icy Insides
Until now, scientists had thought Titan's interior would look a lot like the inside of Jupiter's moon Ganymede: Both bodies are large, have similar densities, and are made of roughly the same materials.
Under Ganymede's thin, icy crust lies a well-defined upper mantle of warmer ice, an inner mantle of silicate, and a molten iron core. (Related blog: "Comets 'Melted' Jupiter's Biggest Moon.")
But the new gravity data suggest that Titan and Ganymede had very different evolutionary histories.
"It is really quite a surprise, and it tells us that [Titan] never got hot enough to separate out into a core, mantle, and crust," said Ulrich Köhler of the German Aerospace Center in Berlin, who wasn't on the study team.
Instead, Iess and colleagues think that Titan's ice and rock remained together in a relatively lukewarm mixture.
This mixture took a leisurely million years or so to settle toward Titan's center—"plenty of time for heat to escape" and for the moon to cool into its present state, Iess said.
The team's calculations support the idea that Titan today has a subsurface liquid ocean from which methane bubbles up through an icy crust, constantly shrouding Titan in thick smog. (Related: "Methane Rain Formed New Lake on Saturn Moon.")
The study's notion of a relatively warm, spongy ice layer beneath a thin, hard outer shell would also explain Titan's lack of major mountains.
"Large mountains can't exist on Titan," Iess said. "They would simply sink into the ice."
Findings published in this week's issue of the journal Science.
Latest News
Most Popular News
-
"Spectacular" Species Off Canada
New pictures reveal a potentially new—and arguably adorable—purple octopus and other rare species found off Canada.
-
Dead Sea Scrolls Mystery Solved?
Recent finds may help reveal who wrote the scrolls. For starters, they may hail from the purported home of the Ark of the Covenant.
-
Recent Global Warming "Undeniable"
The past decade was the hottest on record, a government report says—part of an "unmistakable upward trend."
Advertisement
News Blogs
-
Rangers Trap "Killer" Bear
Grizzly is believed to be responsible for death of a camper and several other attacks.
-
Want to Be an Astronaut?
Find out what it takes, and discover some recent adventures from space.
-
Success for and Against Lions
A new fencing program is protecting livestock and the cats it's made to keep out.
Gulf Oil Spill News and Pictures
-
100s of Gulf Turtle Eggs Relocated
In an effort to save baby sea turtles from the BP oil spill, workers are moving up to 700 nests from the Gulf to Florida's Atlantic coast. Video.
-
Oil Seeps Linked to Another Well
Seeps detected near the Deepwater Horizon wellhead highlight difficulties in teasing out the cause of leaks in the oil-rich Gulf.
National Geographic Magazine
-
Valley of the Whales
The origins of the marine mammal lie buried in Egyptian sand.
-
A Grassland Kingdom
India’s Kaziranga park shelters tigers, buffalo, and rhinos.
Special Ad Section
-
Play Game
Visit river rescue sites and save the ecosystem!
-
Photo Contest
See a selection of photo entries in this year's contest!
