Back in 2010, the Cassini Equinox mission took a colorful snapshot of one of Saturn’s moons in the infrared, Mimas, looking for all the world like a fluorescent-hued Pac-Man. That was because of the unexpected sharply varying temperatures across the moon’s surface, based on the latest data from Cassini’s composite infrared spectrometer. The v-shaped “hot zone” boundary looked remarkably like Pac-Man’s “mouth” on the verge of gobbling the famed Herschel Crater.
And now Cassini scientists have found a second Pac-Man-shaped feature on a Saturnian moon — this time on Tethys, named after the one of the Titans in Greek mythology (as, indeed, are most of Saturn’s moons, thanks to 19th century astronomer John Herschel).
The critical aspect at work here is Mimas’ frozen surface, which should have had smoothly varying temperatures, not the sharp temperature contrasts Cassini’s instruments actually observed. Astronomers figured the colder portions occur because the surface materials in certain areas — low latitudes on that side of the moon that faces forward as it orbits the gas giant — are more thermally conductive.
That means the sun’s rays soak through to the moon’s subsurface, rather than warm the surface. So it doesn’t heat up as quickly in the sunshine, or cool down as quickly at night, compared to the rest of the icy surface.
Something similar appears to be at play on Tethys as well, since it is also made predominantly of water ice, with just a bit of rock tossed into the mix. There is a twist: unlike Mimas, the Tethys Pac-Man can just barely be seen in visible-light images of the moon’s icy surface.
The new data confirms the working hypothesis about the fluctuations in temperature on the moons’ respective surfaces, and should lend insight to the processes at work when shaping planetary moons.
Carly Howett, one of the scientists on the project, said via press release that this means “the processes creating these Pac-Men are more widespread than previously thought. The Saturn system — and even the Jupiter system — could turn out to be a veritable arcade of these characters.”
So apparently the moons of Saturn are just elements in one giant video game. Wocka, wocka wocka!