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Artist Concept of HD 209458b, a Gas Giant orbiting a distant star. 'Hot Jupiters' like it could be all alone in their solar systems.
Photo: NASA/Jet Propulsion Lab
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by Alan McBride
GAINESVILLE, FLA. -- "Hot Jupiter-type" planets are most likely to be alone in their systems, according to research made public by a University of Florida astronomer and others.
"Hot Jupiters" are giant planets beyond our solar system, roughly the size of Jupiter but orbiting close to their parent stars.
They are much hotter than the Earth or Jupiter, and they have very short orbital periods, completing a turn around their stars in fewer than 10 days.
A U-F study, published in the journal Proceedings of the National Academy of Sciences, provides new insights into how they are formed.
This research used information gathered by NASA's planet-hunting Kepler mission, which is tasked with finding Earth-sized worlds.
Along the way, Kepler is also finding worlds that are substantially larger than Earth, and scientists are digging into that data.
Scientists selected a sample of 63 planetary systems containing previously detected hot Jupiter candidates, and looked for signals of additional planets either crossing in front of the host stars or gravitationally tugging on the hot Jupiter's orbit.
In all cases they found no evidence of additional planets.
To allow comparisons, they used the same methods to study a sample of warm Jupiter candidates, equally big planets but located farther away from their parent stars and hot Neptunes; smaller but closer to the stars. They found compelling evidence that at least 10 percent of the warm Jupiters and one third of the hot Neptunes have other planetary companions nearby in the system.
So, what makes the hot Jupiters the lonely planets of the galaxy?
Astronomers said it could be due to the way the hot Jupiters are formed.
Current models suggest that they are probably formed farther away from their host star, and then gravitational interactions with another body caused their orbits to become highly elongated.
Elongated orbits eventually become tighter and more circular, but not before the hot Jupiter has swung through the inner solar systems over the course of eons, sweeping through matter ... and low-mass planets ... within their orbital plane.
Basically, scientists say the hot Jupiters clean out their inner solar systems on their ages-long trip from the fringe to the interior of those systems.
U-F scientists said when a giant planet repeatedly passes through the inner regions of a planetary system on an elongated orbit, it would wreak great havoc on any planets that had formed there.
The other planets would either fall into the star, collide with the hot Jupiter or be kicked out of the system through a gravitational slingshot.
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