Pac-Man on the Moon

Saturn’s moon Mimas must be a fan of 1980s pop culture.

Not satisfied with being labeled the “Death Star moon,” Mimas has now decided to host an interplanetary game of Pac-Man.
paku-paku, paku-paku

Scientists working with NASA’s Cassini orbiter yesterday released the highest resolution heat map to date of daytime temperatures on the icy moon. The map unexpectedly revealed a pattern that’s the spitting image of the video arcade icon.

Even better, the map makes it look as if the galactic Pac-Man is about to chomp down on a red-tinged power pellet in the form of Herschel crater, an 80-mile-wide (128-kilometer-wide) basin that has long been Mimas’s defining feature.

The zany pattern has scientists baffled, as they were expecting to see daytime temperatures more akin to an off-center bull’s eye.

That’s because the sun is directly over Mimas at midday, with lots of sunshine hitting close to the moon’s equator.

A buildup of solar heat should mean that the moon sees its highest temperatures in the early afternoon, creating a pattern rather like the watchful eye of Hal, of 2001: A Space Odyssey fame.
Mimas’s predicted heat map

Instead, when Cassini swooped in for a close flyby of Mimas on February 13, the probe’s composite infrared spectrometer saw heat gathered in a bizarre part-eaten pizza-pie kinda shape.

Of course, heat is a relative term: The “warm” Pac-Man region averages 92 Kelvin (-294 Fahrenheit, or -181 Celsius). That stands out in the temperature data because the cold, bluer region is about 77 Kelvin (-320 Fahrenheit, or -196 Celsius).

The astronomers suggest Mimas might have surface materials in those blue spots that are highly conductive, which means they quickly shuttle heat deeper into the moon.

“It’s maybe something like the difference between old, dense snow and freshly fallen powder,” Cassini team member John Spencer said in a NASA release. Darker, compact snow allows heat to soak through, while fresh, bright white snow acts like an insulator, trapping heat at the surface.

But why Mimas would have such an oddly sharp divide between conducting and insulating materials remains a mystery.

What’s more, Cassini’s close flyby also revealed more subtle temperature differences around Herschel crater that are equally hard to explain.

“Other moons usually grab the spotlight, but it turns out Mimas is more bizarre than we thought it was,” said Cassini project scientist Linda Spilker.

Let’s just hope Cassini’s upcoming April 5 flyby of the hazy moon Titan doesn’t reveal any multicolored ghosts. Otherwise it’s game over, Mimas. Game over.

—All images courtesy NASA/JPL/GSFC/SWRI/SSI

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