A big impact basin gives one of the moons of Saturn a dual personality. From some angles, it makes Mimas look like a giant eyeball. But from others, it gives the moon a more sinister look — like a Star Wars “death star.” And for scientists, the basin is a tool for understanding the structure and history of this intriguing moon.

Mimas is the smallest and closest of Saturn’s major moons. It’s about 250 miles in diameter, and it’s about half as far from Saturn as our moon is from Earth. It may be only a billion years old — less than a quarter of the age of Saturn itself.

The impact basin is called Herschel. It’s about 80 miles across and six miles deep. It was gouged by an impact so powerful that it almost blasted Mimas to bits.

Mimas is made mainly of frozen water, with only a smattering of rock. But there are some oddities in the way it twists back and forth. They suggest that an ocean of liquid water could be buried about 15 or 20 miles below the surface. And according to a recent study, the idea is supported by Herschel’s contours.

The ocean would have been buried much deeper when Herschel was created. Since then, the little moon’s icy crust has gotten thinner — although scientists can’t yet explain why.

Saturn appears near our Moon in the wee hours of tomorrow morning. It stands to the upper left of the Moon at first light, and looks like a bright star.
 

Script by Damond Benningfield