Hot Jupiters found to be loners

So-called hot Jupiter-type planets orbiting distant stars are likely alone in their systems, research by a University of Florida astronomer and others found. Hot Jupiters, giant planets roughly the size of Jupiter but orbiting close to their parent stars -- and thus much hotter than Earth or Jupiter -- have short orbital periods, speeding around their parent stars in fewer than 10 days, astronomer Eric Ford said. Ford and other researchers analyzed data from NASA's Kepler space telescope, looked for signs of additional planets either crossing in front of the host stars or gravitationally tugging on the orbits of hot Jupiters, but found no evidence of additional planets, a university release reported Monday. Astronomers say they believe hot Jupiters are solitary because of the way they form. They are probably formed far from their host star in highly elongated orbits. Researchers say that causes them to pass very close to the host star and then travel far away. The star's gravitational forces affect the planet, causing its orbit to become smaller and more circular, they said -- a process that would remove or destroy other low-mass planets that may have formed initially between the star and the giant planet. "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," Ford said. "The other planets would either fall into the star, collide with the hot Jupiter or be kicked out of the system via a gravitational slingshot."