OUR SOLAR SYSTEM

New 'planetoid' Sedna raises possibility of another Earth-sized object in our Solar System

Scientists can't figure out how Sedna, the most recently-discovered planetoid -- about three-quarters the size of Pluto, came to have such a strange orbit around the Sun. Sedna's path is highly elliptic. It ranges from 76 astronomical units (AU) when it is closest to the Sun to 1,000 AU when it is farthest.
'How on Earth could anything get into an orbit like that,' wonders astronomer Brian Marsden. He suggests another sort of Earth might have had something to do with putting Sedna on its current, odd course.

Richard A. Muller's Nemesis theory -- that our Sun has a companion star responsible for recurring episodes of wholesale death and destruction here on Earth -- seems to reemerge periodically like microbes after a mass extinction. It's a theory that has many detractors. And it's a theory that has been beaten down and left for dead in the minds of most scientists.
Yet it is a theory that just won't die.
Nemesis is cautiously supported by a handful of scientists. Muller meanwhile acknowledges the possibility that the whole idea could turn out to be wrong, but he is nonetheless confident that Nemesis will be found within 10 years.
Nemesis, as Muller sees it, is a dwarf star that would be visible if only we knew which of some 3,000 stars to look at. These are stars that have been cataloged, but their distances are not known. Muller figures Nemesis' orbit ranges from 1 to 3 light-years from the Sun.
On its closest approach, the lethal companion would pass through a vast, but sparsely populated halo of primitive comets called the Oort Cloud, which surrounds our solar system from beyond Neptune's orbit out to nearly a light-year away. (The Sun's nearest known star, Proxima Centauri, is about 4.25 light-years away).
During this passage through or near the Oort Cloud, the gravity of Nemesis would scatter a furious storm of primordial comets that had been relatively undisturbed for 4.5 billion years, since the solar system came into being.