Rings Of Saturn May Be Shedding A New Moon; Astronomer Says He Might Be Watching 'An Act Of Birth'
Saturn is having a baby, and its name is Peggy.
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That is, one of the rings of Saturn appears to be peeling off from the others, and some scientists believe they're witnessing the genesis of the planet's 63rd known moon. "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, of Queen Mary University of London, said in an announcement of the discovery. To the discoverers go the naming rights; these guys called the protrusion Peggy, after Murray's then-80-year-old mother-in-law.
The idea that rings are the precursors to moons, including ours, is a relatively recent one, described by French astrophysicist in Science in 2012. They said that Saturn, Neptune, and Uranus probably all had bigger ring systems than they have today and that the Earth and Pluto probably had rings, too.
In the cases of the latter two, the quick condensation of the rings caused a single main satellite to form: the moon for us, Charon (and a couple of smaller ones) for Pluto. But slow spreading of the gas giants' rings caused multiple moons. "Most regular satellites in the solar system probably formed in this way," they wrote.
Saturn's rings are the largest, and they're an endless source of fascination for NASA. In 1997, a Titan rocket launched a spacecraft called Cassini into space to take up-close pictures of Saturn, 890 million miles away. Since then, it's sent back thousands of stills a year. On April 15, 2013, Cassini sent back the picture shown above. Murray happened to see it with a strange bump on the edge of the A ring, brighter than everything around it. "We hadn't seen anything like this before," he said.
So they went into the records and pulled out any picture they thought might show the same anomaly. Sure enough, they found a bunch. Nine of them are included in their paper, which was published in the journal Icarus.
Murray says it squares with the French moon theory. "The theory holds that Saturn long ago had a much more massive ring system capable of giving birth to larger moons," he says. "As the moons formed near the edge, they depleted the rings and evolved, so the ones that formed earliest are the largest and the farthest out. The mass of the ring system that produced them has been getting smaller with time."
Meanwhile, the older moons are thought to cause the formation of the new ones by tugging at the rings with their gravity. Before Peggy is declared a moon, it has to keep building up enough mass. Right now, its weak gravity is trying to gather up enough ice and dust — which is what all of Saturn's rings and moons are made of — to survive on its own. If it can't, it could just dissolve.
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