A trio of planets orbiting a sun-like star has the most similar layout to our solar system yet seen.
The discovery supports the idea that planets emerge from relatively flat discs of material encircling stars and, at first, orbit neatly in the same plane, just as our eight planets circle the sun. This long-held notion has recently been called into question by a haul of planetary systems with wildly skewed orbits.
Most of these chaotic systems contain hot Jupiters, massive gas giants that circle their stars in a tight embrace. These behemoths frequently have dramatically tilted and sometimes even backward orbits. The big question is whether hot Jupiters form from slanted discs of material or if the planets scatter into odd positions when a tidy system is somehow disrupted by gravitational interactions among its multiple worlds.
Using data from NASA’s Kepler space telescope, a team led by Roberto Sanchis Ojeda of the Massachusetts Institute of Technology examined a star system called Kepler 30 and measured how well the planets’ orbits line up with the star’s rotational plane, something known as obliquity.
They found that the orbits of all three planets nearly align with the star’s equator (Nature, DOI: 10.1038/nature11301). The planets are about four, nine and 12 times the size of Earth and circle far enough from their star that none is considered a hot Jupiter.
Finding more aligned systems free of hot Jupiters would suggest that games of planetary pinball are the primary cause of planets in skewed orbits, say the authors. That would back the idea "that wild, scattered systems are in the minority", says Matthew Payne of the University of Florida, Gainsville, who wasn’t on the team.