Cassini Sees Meteoroids Pummeling Saturn’s Rings

Larry Beck was watching TV last Friday night when he heard a loud crash on his roof. Beck thought something that had fallen off a plane since his home is in the flight path of a nearby airport. When he went into the attic to look, he discovered a hole in his roof and a softball-sized rock, which was soon confirmed as a meteorite. Credit:

The spectacular fireball over Chelyabinsk, Russia in February and a more recent meteorite fall through the roof of a home in Wolcott, Connecticut last Friday remind us the solar system is still littered with debris left over from its formation 4.6 billion years ago.

Piles of small meteorites dropped by the Chelyabinsk fireball on Feb. 15, 2013 and collected by meteorite hunter Mike Farmer. Credit: Mike Farmer

During and immediately after the formation of the planets, meteorite bombardment was nonstop. Since then the impact rate has dropped dramatically – a good thing for life – but continues to this day as a steady rain of everything from fine dust to the occasional teeth-rattling meteorite strike.

Five images of Saturn’s rings, taken by NASA’s Cassini spacecraft between 2009 and 2012, show clouds of material ejected from impacts of small objects into the rings. Click for large version. Credit: NASA/JPL-Caltech/Space Science Institute/Cornell

Besides Earth, amateur and professional astronomers have recorded meteorite or comet strikes on the moon and Jupiter. Now we can add Saturn to the list. Detailed study of thousands of images sent back to Earth by the Cassini spacecraft have turned up nine meteoroid strikes on Saturn’s rings in 2005, 2009 and 2012.

Think of the rings as a giant meteoroid detector/collector. If Earth gathers some 37,000-78,000 tons of space debris per year (mostly as dust but approx. 3-8 tons as rocks weighing 1/3 ounce to 2.2 lbs.), Saturn’s rings, with a surface area 100 times that of our planet, is more like humpback whale during feeding season.

This illustration shows the shearing of an initially circular cloud of debris as a result of the particles in the cloud having differing orbital speeds around Saturn. The numbers in the lower left of the panels in the still image show how quickly a cloud can be elongated as it orbits the planet. Credit: NASA/Cornell

Meteoroids pummeling the rings range in size from about a half-inch to several yards (one cm to several meters). When they bash into the icy ring particles they self-destruct, creating clouds of dust and ice in the process. The material is then sorted according to its distance from the planet – closer debris orbits more quickly, material further out more slowly. Soon the dust cloud gets stretched into an elongated bright streak that Cassini can photograph as it looks down (or up) onto the ring plane.

Detail of a debris cloud from a meteoroid strike in Saturn’s C-ring in 2012. Credit: NASA/JPL-Caltech/Space Science Institute/Cornell

“These new results imply the current-day impact rates for small particles at Saturn are about the same as those at Earth — two very different neighborhoods in our solar system — and this is exciting to see,” said Linda Spilker, Cassini project scientist at NASA’s Jet Propulsion Laboratory in Pasadena, Calif.

It’s fascinating to realize that the sight of a meteor in Earth’s starry skies finds its counterpart among the icy boulders of Saturn’s rings nearly a billion miles afield.