Are Planetary Systems Filled to Capacity?

Such interactions also caused the orbits of the major planets to migrate. Because the growing planets Saturn, Uranus and Neptune tossed more small bodies inward toward the orbit of Jupiter than out of the solar system, those planets migrated outward, to conserve the total angular momentum. But the much more massive planet Jupiter ejected most of the small bodies it encountered into the outer solar system and beyond, and it consequently migrated inward. When the solar system was forming, the Kuiper belt contained hundreds of times more mass than it does today. The objects now in the belt represent only the small fraction that managed to survive. The same is true of the asteroid belt. Gravitational sculpting by the planets has severely depleted both populations, leaving the Kuiper and asteroid belts as remnants of the primordial planetesimal disk. Whereas some mean-motion resonant orbits in the solar system are highly unstable, others are quite resistant to disruption.

The subtitle is, "Computer simulations suggest that the answer may be yes. But observations of extrasolar systems will provide the ultimate test" -- that has already shown to be a crock. Due to the limitations of observing machinery of various kinds, the first extrasolar planets found were larger than Jupiter and orbiting very close to their parent stars. It is generally agreed that they could not have originated in their current orbits; either they originated much further out, but have been migrating slowly inward toward destruction (i.e., they move in retrograde), or they were captured into orbit by the stars, or they are of more recent origin and are made of hurled off debris from the the stars themselves. One could argue that these earliest discoveries are unusual systems, and that they will be submerged in the data stream of thousands of discoveries to be made in the future, but that doesn't change the fact that a large number of those already known don't fit his description at all.

Are Debris Disks and Massive Planets Correlated? [abstract]
Amaya Moro-Martin, John M. Carpenter, Michael R. Meyer,
Lynne A. Hillenbrand, Renu Malhotra, David Hollenbach,
Joan Najita, Thomas Henning, Jinyoung S. Kim,
Jeroen Bouwman, Murray D. Silverstone, Dean C. Hines,
Sebastian Wolf, Illaria Pascucci, Eric E. Mamajek,
Jonathan Lunine
Using data from the Spitzer Space Telescope Legacy Science Program "Formation and Evolution of Planetary Systems" (FEPS), we have searched for debris disks around 9 FGK stars (2-10 Gyr), known from radial velocity (RV) studies to have one or more massive planets. Only one of the sources, HD 38529, has excess emission above the stellar photosphere; at 70 micron the signal-to-noise ratio in the excess is 4.7 while at wavelengths < 30 micron there is no evidence of excess. The remaining sources show no excesses at any Spitzer wavelengths. Applying survival tests to the FEPS sample and the results for the FGK survey published in Bryden et al. (2006), we do not find a significant correlation between the frequency and properties of debris disks and the presence of close-in planets. We discuss possible reasons for the lack of a correlation.
Stars Swallow Planets and Researchers Have Proof
by Harald Franzen
May 10, 2001
A light spectrum analysis of HD82943â€”a star slightly hotter and larger than the sun, harboring its own planetary systemâ€”revealed that it contained traces of an isotope of lithium called Lithium-6, or 6Li. Although 6Li is common in planets, it burns up quickly in stars after they are born and thus shouldn't exist in a star like HD82943... To confirm their theory, the scientists looked at another star that shared HD82943's characteristics except that it did not have planets. In keeping, they found that did not have 6Li in its spectrum. The researchers hope that this finding will help to explain how so-called exoplanets form and if this kind of cannibalism is a common process.
Metal Ring Round White Dwarf Solves Missing Planets Puzzle
SpaceRef
Saturday, December 23, 2006
Astrophysicists at the University of Warwick have found an unusual ring of metal-rich gas orbiting very close around a white dwarf star. The presence of the ring helps solve a problem for astronomers who, up till now, have been puzzled by the apparent absence of planets around white dwarf stars... This "metal" disc around SDSS1228+1040 appears to be relatively rare. Before their study, three white dwarfs, out of a study of a few hundred, were suggested to be surrounded by planetary debris material. However, in none of those three cases could a definite proof of an asteroid origin be made due to the lack of information on the geometry and the chemical abundance of the material found in the vicinity of these stars. As part of their study, the Warwick team investigated data for 500 additional white dwarfs without finding conclusive evidence for another system harbouring such a disc.
Rogue Planet Find Makes Astronomers Ponder Theory
by Maggie Fox
October 5, 2000
Eighteen rogue planets that seem to have broken all the rules about being born from a central, controlling sun may force a rethink about how planets form, astronomers said on Thursday... "The formation of young, free-floating, planetary-mass objects like these is difficult to explain by our current models of how planets form," Zapatero-Osorio said... They are not linked to one another in an orbit, but do move together as a cluster, she said... Many stars in our own galaxy, the Milky Way, may have formed in a similar manner to the Orion stars, she said. So there could be similar, hard-to-see planets floating around free near the Solar System.
55 Cancri
by James B. Kaler
The Planet Project
Farthest out, at 5.9 Astronomical Units (AU) from the star, is the most massive, 55 Cnc-d, which is at least 4.1 times the mass of Jupiter and takes 14.7 years to orbit. The other three are much closer and less massive. Next in order are 55 Cnc c, b, and e with minimum masses of 0.21, 0.84, 0.045 solar, orbital radii of 0.24, 0.11, 0.038 AU, and periods of 44, 14.7, and 2.81 days. The existence of 55 Cnc-c is questionable. 55 Cnc-e has the smallest measured minimum mass, only about that of Uranus or Neptune. It is also closest to its parent star, its orbit just 10 percent the size of that of Mercury... 55 Cancri is a mid-sixth magnitude star (magnitude 5.95) class G (G8) dwarf 41 years away. A bit cooler (5280 Kelvin) and carrying only 0.87 of a solar mass, it shines at just 58 percent of the luminosity of the Sun, its radius 0.9 solar.

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