Satellite smashups could have given birth to Saturn’s odd moons

Weird moons orbiting the ringed planet might have been forged from head-on collisions

Saturn moons and simulated moons

SPITTING IMAGE  Simulated collisions between two moonlets can lead to oddly shaped moons (bottom row) that closely resemble some of Saturn’s moons (top row; from left to right: Pan, Atlas and Prometheus).

Images: JPL-Caltech/NASA, Space Science Institute; Simulations: A. Leleu, M. Jutzi and M. Rubin/Nature Astronomy 2018

A space ravioli. A planetary baguette. A cosmic Kaiser roll. Some of Saturn’s moons have shapes that are strangely reminiscent of culinary concoctions.

Images of the oddball moons, mostly from the now-defunct Cassini spacecraft (SN Online: 9/15/17), got planetary scientists wondering how these satellites ended up with such strange shapes. Now, researchers suggest that collisions between young moonlets could have done the job, according to a study published online May 21 in Nature Astronomy.

Adrien Leleu , a planetary scientist at the University of Bern in Switzerland, and colleagues developed computer simulations that let the scientists virtually smack together similar-sized moonlets at various speeds and angles. The team found that, at low angles and relative speeds of tens of meters per second (roughly equal to a car on country roads), impacts can create offbeat shapes that look like the misfits around Saturn.

Head-on collisions result in a flattened moon like Pan, which resembles an empanada (SN Online: 3/10/17). An impact angle of just a few degrees leads to an elongated satellite such as Prometheus, which looks like a French loaf.

Not all run-ins create a weird looking moon. At higher angles, for example, moonlets might hit and run. Or they could form highly elongated rotating moons that subsequently break apart.

Leleu and collaborators focused on the smaller moons of Saturn that orbit within the planet’s rings. But the team also found that a similar collision between two larger moonlets could also account for the odd shape of Iapetus (SN Online: 4/21/14), a more distant walnut-shaped moon with a pronounced ridge along its equator that has puzzled scientists since the belt’s discovery. Other speculative origins for the ridge include volcanoes, plate tectonics or ring debris that rained down on the moon.

Christopher Crockett is an Associate News Editor. He was formerly the astronomy writer from 2014 to 2017, and he has a Ph.D. in astronomy from the University of California, Los Angeles.

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