Planetary Systems Compared To Pancakes
October 15, 2012

Majority Of Planetary Systems ‘Flatter Than Pancakes’

Lee Rannals for - Your Universe Online

Astronomers from UCLA using NASA's Kepler space telescope have determined that most planetary systems are "flatter than pancakes."

The team wrote in a paper submitted to the Astrophysical Journal that they developed a computer model of planetary systems and compared them to the properties of Kepler data.

They found that the more than 85 percent of planets have inclinations of less than three degrees, making the planetary systems very flat.

The scientists looked at the trajectories of planets around the host star and found that the trajectories are closely aligned in a pancake-like geometry, similar to planets in our own solar system.

These flat orbits imply low relative inclinations with planets all orbiting near the same plane, according to UCLA graduate student Julia Fang.

"Next time you eat a thin-crust pizza, you can get a sense of the flatness of a typical planetary system," said UCLA professor Jean-Luc Margot.

The researchers said that one motivation for the study was to compare the properties of these Kepler planetary systems to the solar system and determine how typical the solar system is.

Seven out of the eight planets in our solar system have inclinations of less than three degrees, with Mercury as the exception.

"It looks like our results are consistent with the flatness also evident in the planetary orbits in our solar system," Fang said. "Our solar system may be common compared to other planetary systems in this regard. Perhaps we're not that special."

Margot said he made pancakes with a mean thickness of a little under a quarter of an inch, and a mean radius of about 2.5 inches.

"This corresponds to inclinations of six degrees. So most planetary systems are flatter than pancakes, by about a factor of two," Margot said. "The best mental image for the geometry of planetary systems is somewhere between a crepe and a pancake."

The team's models of planetary systems also yielded the typical numbers of planets per planetary system.

They found that for orbital periods out of 200 days, about 75 percent of systems have one or two planets.

The scientists will be able to use data from the Kepler mission to extend their study to longer orbital periods.

The launch of Kepler and its discoveries has been able to play a key role in research for planetary astronomers.

"Kepler is an amazing telescope in space; so far it has discovered a treasure trove of planets totaling more than 2,300 candidates," Fang said.

The telescope stares at over 100,000 stars for glimpses of planets crossing in front of the stars. This is like staring at more than 100,000 car headlights a few miles away to look for the dimming due to a mosquito crawling across the headlight.

"Our study has begun finding answers to fundamentally important questions in planetary astronomy," Fang said. "We'll be presenting exciting results at upcoming conferences."

The astronomers will continue to study planets discovered by Kepler to learn more about their dynamical properties.