By Ron Cowen
Planetary scientist Mike Brown has had plenty of practice finding objects at the fringes of the solar system. In sky images spaced an hour apart, he and his colleagues have identified several of the solar system’s most distant denizens, revealed by their motion relative to the background of fixed stars. Early in 2004, soon after his team began using a new version of their discovery software, Brown was in his office at the California Institute of Technology in Pasadena reviewing images on his computer screen. He came across a sequence of pictures, taken by the Samuel Oschin telescope on Palomar Mountain near Escondido, Calif., showing a faint object moving so slowly that it must have been in the outer solar system, far beyond Pluto. “I think I fell out of my chair,” says Brown.
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The extremely slow motion of the object, now dubbed Sedna (SN: 3/20/04, p. 179: Planetoid on the Fringe: Solar system record breaker), indicates that the body lies so far out that “there is nothing in the solar system today that could have ever made it … and if you run time backwards, there’s nothing in the solar system today that can put [a body] in this orbit,” says Brown. Finding Sedna, he adds, “just blew our minds.”