Boffins analysing early data from NASA's exoplanet-hunting Kepler space telescope say they've been surprised to detect an unexpectedly large number of star systems with multiple planets.
Kepler spots planets orbiting other suns by noting the changes in the light emitted by the star when a planet transits in front of it. The scope can thus only see planets whose orbital plane is edge-on to us. Even a slight tilt will mean that Kepler cannot see a given planet, and thus scientists didn't expect to see many stars with more than one planet passing in front of them: even where a star had multiple worlds orbiting it, generally only one of them would be spotted.
As an example, an alien Kepler looking at our solar system from some directions and seeing Earth would miss Mercury and Venus, as their orbits are slightly tilted with respect to ours.
But Kepler is in fact actually seeing a lot of very flat solar systems with planetary orbits closely aligned.
"We didn't anticipate that we would find so many multiple-transit systems. We thought we might see two or three. Instead, we found more than 100," said astronomer David Latham (of the Harvard-Smithsonian Center for Astrophysics) at a press conference in Boston today.
To be specific, of the 1,200+ possible planets picked up so far by Kepler, some 408 are in flat, multi-transit systems.
Latham and his fellow boffins think that the flat systems exist because they have no massive gas-giant worlds like our own Jupiter, which could affect other planets' orbits with their strong gravity.
"Jupiters are the 800-pound gorillas stirring things up during the early history of these systems," explained Latham. Kepler's newly found flat-system worlds are mostly smaller than Neptune: comparative tiddlers.
The scientists are particularly excited to have so many multiplanet systems to work on, because such systems allow them to deploy an extra analytical tool in which the planets' gravitational effects on the timing of each other's transits are measured.
"These planets are pulling and pushing on each other, and we can measure that," said Latham's fellow astronomer Matthew Holman. "Dozens of the systems Kepler found show signs of transit timing variations."
This extra handle on planetary sizes and orbits around other stars could be a key boffinry leg-up in finding and verifying the first rocky exoplanets known to be at such a distance from their parent suns as to allow liquid water to exist on their surfaces. Worlds of this sort are of great interest as they could be habitable – or even inhabited by alien life along the same general lines as that of Earth. ®