Washington: A new picture of Titan has revealed that Saturn’s largest moon has surprisingly slushy insides with no clear layers.
According to a report in National Geographic News, 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 slushy mix with no clearly defined rocky layers.
Until now, scientists had thought that Titan’s interior would look a lot like the inside of Jupiter’s moon Ganymede, as 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.
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 Kohler of the German Aerospace Center in Berlin.
Instead, Iess and colleagues think that Titan’s ice and rock remained mixed together in a relatively lukewarm mush.
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, according to Iess.
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.
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. They would simply sink into the ice,” Iess said.