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.
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.
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.
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.
“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.