The moons that orbit Saturn may be increasing by one -- an icy, pint-sized object that astronomers have named “Peggy.”
NASA’s Cassini spacecraft has spotted evidence that a mysterious object measuring perhaps half a mile across is disturbing the outer edge of Saturn’s large, bright A ring. The object’s gravity seems to have roughed up the ring’s usually smooth profile.
As a result, a stretch of the A ring that measures 750 miles long and 6 miles wide is now about 20% brighter than it would typically appear. The fuzzy blob on the A ring’s edge was imaged by Cassini’s narrow-angle camera exactly one year ago, on April 15, 2013.
Peggy, which is believed to have caused this mess, is too small for Cassini to see directly. But NASA scientists hope to get a closer look in late 2016, when Cassini is scheduled to fly near the A ring.
There’s good reason to think Peggy could join the very long list of Saturnian moons (a list that includes 53 official moons and nine provisional ones). Astronomers have theorized that the moons started out as collections of ice from Saturn’s hefty rings and then drifted into orbits farther away.
The oldest moons probably formed when the rings were more substantial. By coalescing so much material, they grew large and drifted into orbits farther away from the planet.
Younger moons, on the other hand, tend to be smaller and closer in. If Peggy is indeed a moon, it would certainly seem to be following that pattern.
“We may be looking at the act of birth, where this object is just leaving the rings and heading off to be a moon in its own right,” Carl Murray, an astronomer at Queen Mary University of London, said in a statement from NASA. “We have not seen anything like this before.”
Murray is the lead author of a report on Peggy that was published online Monday in the journal Icarus.
Peggy -- named after Murray’s mother-in-law, according to reports -- is probably as big as it’s ever going to get. It might even be coming apart, according to NASA. But it may still be able to give scientists clues about how Saturn’s dozens of other moons came to be.