I found an interesting link at spacedaily.com today. Apparently the planetoid Sedna, a Pluto-type Kuiper belt object, may be explained by a second star in the solar system. The hypothesis that the sun might be part of a binary system isn't new, but this is the first good evidence in its favor for a long time. Sedna's orbit reportedly fits pretty closely with the orbit expected of a theoretical second star, but is not very well explained by other forces. If such a star exists, it must surely be a red or brown dwarf, since it has never been seen. It can't be a black hole, which would have been much much easier to spot, unless said black hole is quiescent right now. (There's a cheery thought, huh?)

The other star, if it exists, would be named Nemesis. It's just a theory for now, but if it exists, future star- and planet-finding projects may detect it. Barnard's star, just under 6 light-years from us, is a red dwarf that's very dim, but was detected due to its motion relative to other stars. If a star that close can be missed, then one that's 1 to 1.5 light-years away could also escape detection if it's a similar or dimmer model. Nemesis was first proposed to explain what were thought to be periodic mass-extinctions, caused by perturbation of the Oort cloud that sent comets hurtling inward toward the inner planets; other theories suggest no such periodic timetable ever existed, or that the sun crossing the galactic plane could have the same effect.

When looking up binary stars on Wikipedia, I discovered another interesting fact. In a related link, astronomers hypothesize based on computer models that terrestrial planets may be more common in binary systems. However that story is looking at models of binaries that have up to maybe 12, 15 AU separation between them at most. Nemesis is suggested to be about 50,000 to 100,000 AU away from the sun. One does wonder, though, if it would have a unique impact on planetary formation or orbital stability that might explain why Earth has a nearly circular orbit.

Also in the story on Sedna, it's mentioned that the recently discovered Kuiper belt object UB313 (sometimes called "Xena" while it's awaiting a more official name) is bigger than Pluto. I discovered elsewhere that its potential status as a 10th planet is under debate. Its official name may end up being Lila. A proposed name for its moon is Gabrielle. Apparently in the rush of new objects detected by early astronomy, all the Greco-Roman god names were taken, leaving us with Geoff the god of biscuits and Simon the god of hairdos.