From 1989 to 1994, the Perseid meteors, which occur every August, came in bright staccato bursts. One particular night in 1993 stood out to observers in Europe.

“It’s known as the night of the howling dogs,” says Peter Jenniskens of the SETI Institute in Mountain View, California. “Meteor observers were so excited with the oohs and the ahs that the dogs in the neighbourhood picked up on that.”

But we didn’t know why so many meteors were clustered together. “This series of outbursts was not well explained,” says Jenniskens.

Now a team led by Aswin Sekhar at the University of Oslo in Norway thinks it may have an answer: a rare gravitational dance between the Perseids, Saturn and Jupiter.

The Perseid meteors are fragments of ice and rock ejected by Comet Swift-Tuttle, which swings into the inner solar system every 133 years. When Earth passes through this stream of debris each year, our skies light up with meteor showers.

But at key locations in the Perseid stream, meteors may clump together thanks to gravitational nudges from what’s called a three-body orbital resonance. “For one orbital period of the Perseid particles, you have 10 revolutions of Jupiter and four of Saturn in the same time,” Sekhar says.

Perseids prediction

The fact that these two planets’ orbital periods are whole number multiples of the Perseids’s “year” is extremely rare, but we know of other instances of orbital resonance in the solar system. Take Jupiter’s moons: for every trip of Ganymede around Jupiter, Europa goes around twice and Io four times. But this is the first time such a resonance has been found for a meteor stream.

Sekhar thinks the intense showers of the early 1990s were caused, at least in part, when Earth passed through a dense clump of Perseids herded together by the resonance.

But it will take a while to reach peak Perseid again. “My predictions say that 2111 is a good year,” he says. “Hopefully in the next work we will find something sooner.”

Currently, Sekhar and his colleagues are trying to predict smaller, near-future outbursts of the Perseids that observers could look out for.

“The next step is to come up with more precise predictions of when they would expect these enhancements to occur,” says Jenniskens. But in the meantime, he thinks it’s a compelling suggestion.

“I’m very intrigued,” he says. “Maybe they’ve stumbled on to why there was such a thing as the night of the howling dogs.”

Source: New Scientist