From the Trible Sunset article
The heat coming from a nearby star frustrates the initial stages of giant planet formation -- the gluing together of planetary seeds, called cores. Therefore, the typical hot Jupiter is thought to form farther out -- beyond a theoretical limit called the snow line.
"Past about 3 AU, it is cold enough to form ices and other solid material for building cores," Maciej Konacki of the California Institute of Technology said. An AU is the distance between the Sun and the Earth -- about 93 million miles.
Once a sufficiently large core is built outside the snow line, the planet can start accreting gas and -- if the conditions are right -- migrate toward its sun.
Although this scenario appears to work in most stellar systems, it has difficulty explaining the newly-discovered planet in HD 188753. Of all the planet-harboring stars known, this is the closest that a stellar companion has ever been found.
"The problem is that the pair is a massive perturber to the system," Konacki said. "Together, these two stars are more massive than the main star."
Moreover, the pair goes around the primary along an oblong orbit that stretches from 6 AU out to 18 AU over a 26 year period. This eccentricity increases the instability of the disk around the primary. Konacki estimates that due to the gravitational perturbations from the pair, the proto-planetary disk was truncated down to 1.3 AU, far within the snow line.
"How that planet formed in such a complicated setting is very puzzling. I believe there is yet much to be learned about how giant planets are formed," Konacki said.
(Quote edited to identify the speaker and affiliation.)
