Saturn has another Pac-Man moon

Posted by Kate Taylor

Cassini scientists have found a second 'Pac-Man' moon orbiting Saturn, this time on the moon Tethys.

In 2010, the team discovered that thermal imaging of the icy moon Mimas revealed a shape just like a Pac-Man eating a dot, with warmer areas making up the Pac-Man shape.

"Finding a second Pac-Man in the Saturn system tells us that the processes creating these Pac-Men are more widespread than previously thought," says team member Carly Howett. "The Saturn system - and even the Jupiter system - could turn out to be a veritable arcade of these characters."

The scientists theorize that the shape occurs because high-energy electrons bombard low latitudes on the side of the moon that's facing forward as it orbits around Saturn, turning that part of the fluffy surface into hard-packed ice. As a result, the surface doesn't heat as rapidly in the sunshine or cool down as quickly at night as the rest of the surface.

Finding another Pac-Man on Tethys confirms that high-energy electrons can dramatically alter the surface of an icy moon. And because the altered region on Tethys, unlike on Mimas, is also bombarded by icy particles from Enceladus' plumes, it implies the surface alteration is occurring more quickly than its recoating by plume particles.

"Studies at infrared wavelengths give us a tremendous amount of information about the processes that shape planets and moons," says Mike Flasar, the spectrometer's principal investigator. "A result like this underscores just how powerful these observations are."

The new images were taken in September2011, and show daytime temperatures inside the mouth of Pac-Man to be cooler than their surroundings by 29 degrees Fahrenheit. The warmest temperature recorded was minus 300 degrees Fahrenheit - slightly cooler than the warmest temperature at Mimas.

At Tethys, unlike Mimas, the Pac-Man pattern can also be seen subtly in visible-light images of the surface, as a dark lens-shaped region. This brightness variation was first noticed by NASA's Voyager spacecraft in 1980.

"Finding a new Pac-Man demonstrates the diversity of processes at work in the Saturn system," says Cassini scientist Linda Spilker. "Future Cassini observations may reveal other new phenomena that will surprise us and help us better understand the evolution of moons in the Saturn system and beyond."