No, that's not Death Star - rather, it's a strange walnut-shaped moon of Saturn. Scientists have just solved the mystery of its weird shape:

There's a strange moon whizzing around Saturn that's shaped, oddly, like a walnut.

Now astronomers find that Iapetus got its nutty shape from a super-fast spin that was frozen into place early in the solar system's formation.

When the Cassini spacecraft snapped close-ups of Saturn's moons in 2005, it revealed a bulging waistline of rock along the equator of the now slowly spinning Iapetus. Astronomers think this characteristic shape persists because Iapetus was cryogenically frozen in time about 3 billion years ago, during the moon's "teen" years.

"Iapetus spun fast, froze young and left behind a body with lasting curves," said Julie Castillo, a Cassini scientist at NASA's Jet Propulsion Laboratory (JPL) in Pasadena, Calif.

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