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

You probably havent been waiting on this announcement with as much bated breath as for, say, the first Suri Cruise photos, but just weeks after officially kicking Pluto out of the band formerly known as the Nine Planets, the International Astronomical Union has decided on the name Eris for the space rock 2003 UB313. Eris, Plutos Kuiper Belt mate, helped fuel the whole Whats a planet? controversy following its 2003 discovery, when astronomers realized it was larger than Pluto.

Before becoming Eris, the dwarf planet had a public identity crisis that would make even Diddy jealous. Its discoverer, Caltech astronomer Michael Brown, first suggested Xena, of warrior-princess fame, which was adopted by many media outlets in favor of the stodgy yet official 2003 UB313. Brown later suggested Lila after his newborn daughter and, most recently, Persephone, the mythical wife of Pluto, ruler of the underworld, but that name already belonged to an asteroid.

After a quick refresher on Greek mythology, however, Eris is clearly the most appropriate choice anyway. Eris is the Greek goddess of discord and strife, exceptionally proficient at stirring up jealousy and envy to cause fighting and anger among men. At the wedding of Peleus and Thetis, the parents of the Greek hero Achilles, all the gods were invited with the exception of Eris. Enraged at her exclusion, she spitefully caused a quarrel among the goddesses that led to the Trojan War. What a spitfire. —Bjorn Carey

The twin Mars rovers, Spirit and Opportunity, have observed more than 4,000 geographical features on the planet since they landed in January 2004. Expected to run for only three months, the rovers are still going strong, and their mission has now been extended to at least September of next year. They've been ranging for so long, in fact, that they're causing a problem for their handlers. In order to document the terrain efficiently, scientists have had to come up with unique names for all the features the rovers discover, a task that gets tougher with each passing day.