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“Ping Pong” Planets

By David Reneke

News from the space and astronomy communities around the world.

David Reneke is an astronomy lecturer and teacher, a feature writer for major Australian newspapers and magazines, and a science correspondent for ABC and commercial radio. Subscribe to David’s free Astro-Space newsletter at

The full text of this article can be purchased from Informit.

A gravitational tug of war more than a million years old could be in play between nearby binary stars. It’s generally accepted that planets can be ejected from solar systems, especially during the dynamic and unstable period early in the solar system’s life where planets are jostling for the most stable orbits.

Astronomers have recently found exoplanets in double and even triple star systems, and in a new study, Nickolas Moeckel and Dimitri Veras of the Institute of Astronomy, Cambridge, found that a planet ejected from orbit around one star could find itself passed onto its binary companion.

It’s more than a good bet that the planet may then find itself “bounced” between the stars, providing one possible explanation for the eccentric orbits of some exoplanets. Taken to the extreme, planets could be kicked out of one star’s clutches only to be sent careening around, or into, its binary companion.

Moeckel feels there are two key prerequisites for this phenomenon. “First, the stars need to be on a wide enough orbit so that one is not interfering with planet formation around the other. Second, there needs to be multiple planets around one of the stars,” he said.

Researchers are in agreement on one thing: the orbital instability that leads to the bouncing phenomenon requires that two planets come in close proximity to each other. In fact, they say it...

The full text of this article can be purchased from Informit.