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Strange New 'Twin' Worlds Found
toomanyairmiles writes "The BBC reports on the the discovery of 'twin worlds' which orbit each other, successfully blurring the line between planets and stars. 'Their existence challenges current theories about the formation of planets and stars.' according to the Journal of Science article which reports their existence. 'The pair belongs to what some astronomers believe is a new class of planet-like objects floating through space; so-called planetary mass objects, or "planemos", which are not bound to stars.'"
Anticipating a possible question: no, a previously-unknown population of "planemos" can't be the dark matter astronomers are searching for. First, there were enough of them to account for the huge mass of dark matter (some 95 percent of the mass of the universe), we would have seen a lot more of them by now. "Massive compact halo objects", or basically planetoids, brown dwarfs, neutron stars, etc. have been detected (via gravitational lensing), but they are known not to comprise the majority of dark matter due to such bounds on their total mass. Furthermore, from the effects of dark matter on structure formation in the early universe, the cosmic background radiation, and other factors, it is known that "normal" matter can't account for most of the mass of dark matter, either: most of it needs to be in the form of "weakly interactive massive particles" (sort of analogous to neutrinos, except much heavier).
technically they do... a planetary object by definition needs something to orbit.
What i think you meen is that a nebula of the right size can form a stelar object that doesnt have the mass for fusion.
pluto is thought to be a captured kuiper belt object,, meaning that some collision or gravitational interaction with a massive body brought it in towards the inner solar system, which explains its eccentric orbit which is also at a very high inclination to the plane of the ecliptic.
You are incorrect as to why the planets are on the same elliptical plane.
http://www.nineplanets.org/origin.html
#3 on that page is the step which explains why the solar system is on the same plane. Pluto being outside that plane is most likely it is actually a kupier belt object and was far enough out from the formation of our sun to not have fully fallen into the accretion disc.
More information is available at http://en.wikipedia.org/wiki/Accretion_disc
http://en.wikipedia.org/wiki/Protoplanetary_disc
The reason your explanation doesn't work for why the planetary bodies are on the same plane is because they are all in stable orbits. To plane out into a disc they would need to still be falling towards the sun.
Planetary rings are in the ring pattern because they follow the orbit of the object from which they were created, they are not collected and built up from smaller particles but probably the result of the destruction of a large object.
http://en.wikipedia.org/wiki/Planetary_rings
They both orbit around their common center of mass, as do all pairs of orbiting bodies. The moon and earth actually orbit around a point 4700km from the earths center.
"Prefiero morir de pie que vivir siempre arrodillado!"