"Before the first extrasolar planets were discovered, astronomers had high confidence that other solar systems would resemble ours. We have rocky planets close to the sun, and gas giants farther out. Planetary scientists were pretty sure the pattern would hold up around other stars. Now that we have hundreds of examples to compare, the reality has been far different from expectations. The number of surprises in real exoplanet systems underscores the potential flaws in building models based on a sample size of one...
There are so many surprises in this field—almost nothing is turning out as we expected. There are Jupiter-mass planets in three-day orbits. There are planets with masses that are between those of the terrestrial planets in our solar system and the gas giants in the outer part of our solar system. There are Jupiter-mass planets with hugely inflated radii—at densities far lower than what we thought were possible for a gas-giant planet. There are giant planets with gigantic solid cores that defy models of planet formation, which say there shouldn’t be enough solids available in a protoplanetary disk to form a planet that dense. There are planets with tilted orbits. There are planets that orbit the poles of their stars, in so-called circumpolar orbits. There are planets that orbit retrograde—that is, they orbit in the opposite direction of their star’s rotation. There are systems of planets that are in configurations that are hard to describe given our understanding of planet formation. For instance, some planets are much too close to one another."
"The discovery of a fourth giant planet orbiting the star HR 8799 marks a big find for exoplanetary observers, but it also casts doubt on long held theories of how worlds are formed...
However, the fact that these massive worlds are orbiting so far, and so close, to their star directly contradicts leading theories of how planets are born.
Worlds are thought to be formed either by "accretion" -- where small clumps of dust build up into a rocky inner core over a few million years and then gravity pulls gases toward it, or "fragmention" -- where sections of the galactic disc suddenly collapse into a planet, over the course of about 10 thousand years.
The four exoplanets surrounding HR 8799 can't be explained by either theory. The three outer planets would be so far away, and the dust moves so slowly, that by the time the dust had balled up into a rocky core by accretion, the gases surrounding the star would be long gone. The closest inner planet -- our newly discovered HR 8799e -- on the other hand, orbits so close to the star that it would be far too hot for the disc to collapse inward, as explained by the fragmentation theory."
"However, astronomers are puzzled by the fact that the planet is so close to the parent star. According to orbital migration theory, which is currently the leading model of planetary formation, the gravitational pull of the other two stars should have stripped away the protoplanetary disk from the parent star. This disk contains the gas and condensed matter from which planets are thought to form.
"How that planet formed in such a complicated setting is very puzzling," says Konacki. "Planets from complicated stellar systems will put our theories of planet formation to a strict test.""
Even more interesting, many of the astronomers in these science articles are talking about planetary migration, where planets change orbits within their solar system, a theory once espoused by a very controversial scholar in academic circles, I might add...
Post Edited (29-Jan-13 05:43)