In the Solar System, 53 is a Crowd

SAN FRANCISCO--Caltech astronomer and planet hunter Mike Brown continued his assault on the recently-downgraded Pluto today during a lecture titled "How I Killed Pluto and Why It Had It Coming" at the annual American Association for the Advancement of Science conference.

It was Brown's discovery of Eris, the Kuiper Belt Object slightly larger than Pluto, that finally forced the International Astronomical Union to define just what is and isn't a planet back in August. Under one IAU proposal, the number of planets in the solar system would have ballooned to 53, including Brown's find, Eris. However, that idea was deemed ridiculous by world class astronomers and kindergarten teachers alike, and a few days later the current eight planet ruling came down and kicked Pluto to the curb. Even though the ruling meant that Brown's find wasn't, in fact, a planet, he's a fan of the eight planet system. "Who says that 53 is too many? I do," Brown said. "I want my planets to mean something." Plus, he really seems to hate Pluto and surely took some twisted pleasure in knocking it down a notch.

Brown also took us on a tour of some other interesting Kuiper Belt Objects, including what he considers the "coolest object in the universe," a bright, rapidly-rotating oblong thingy (136108) 2003 EL61, also known as "Santa." Santa is one of roughly 800 known wonky KBOs, which many astronomers study to learn what the conditions were like when our solar system was pulling itself together. If Santa is any indication, there was a lot of ice and rocks.

Even further away from the Sun is the Trans-Neptunian object Sedna, which Brown was extremely lucky to spot back in 2003: Because the object takes 12,000 years to orbit the sun on its extremely egg-shaped path, there is only a 200-year-window each orbit during which it's close enough to Earth to be visible. Sedna runs about 75 percent the size of Pluto, and Brown estimates that there could be another 50 to 60 similarly-sized objects following a similar orbit. And, he continued, if there are that many Sedna-sized objects, there's a good chance that there are a dozen or so Mecury-sized rocks, and perhaps even a couple planets the size of Earth. Just when you thought memorizing the solar system's planets had gotten a little easier.--Bjorn Carey