Close-Up of A Saturnian Moon
Astronomers who recently discovered the so-called 10th planet have also found what may be the weirdest object in the solar system: a Pluto-size orbiter shaped like a squashed football. EL61, as it is officially known, is a mass of ice and rock that flops through space with a spin rate far faster than that of any known body its size, making complete rotations around its wide axis every four hours.
Photo courtesy NASA/JPL/Space Science Institute
A surprising new look: Before Cassini took this close-up of Saturn's moon Hyperion, astronomers had no idea the tiny satellite was craggy and spongelike.
"People ask us, 'Are you sure it's rotating that quickly?' " says Yale University astronomer David Rabinowitz. "It's hard to believe. But our data is unambiguous."
Rabinowitz is part of a United States team that reported EL61's discovery one day after an identical announcement by Spanish astronomers. The coincidence is steeped in controversy, with the U.S. team accusing the Spanish team of cribbing their data. But the dispute does not detract from the thrill of the discovery.
The planetoid is the strangest of several new bodies discovered in the solar system's icy fringe, the Kuiper belt. This region of deep space is filled with detritus from the early universe that was probably flung there by the gravity of large planets like Jupiter. EL61 may have been compressed into its shape by eons of breakneck spin. Why something so large revolves so quickly is a different question. Perhaps an equally massive object slammed into it long ago, Rabinowitz says. "Certainly in the early solar system things got knocked around quite a bit."
Rabinowitz was surprised to find a tiny moon orbiting the planetoid. Nothing quite like this pair had been seen before, but as telescopes improve, squashed footballs with boulder-size satellites may not be so unusual for long. "We've only known about the Kuiper belt for a short time, and we know next to nothing about how the solar system formed," says Rabinowitz. "I'm sure we'll see things that are much odder."