Metzger recommends classifying a planet based on if it is large enough that its gravity allows it to become spherical in shape.
"And that's not just an arbitrary definition, Metzger said. "It turns out this is an important milestone in the evolution of a planetary body, because apparently when it happens, it initiates active geology in the body."
Pluto, for instance, has an underground ocean, a multilayer atmosphere, organic compounds, evidence of ancient lakes and multiple moons, he said.
"It's more dynamic and alive than Mars," Metzger said. "The only planet that has more complex geology is the Earth."
Uncle Bob's would like to apologize to the following people or groups of people who we undoubtedly have offended over the course of the past few years. If you feel you have been personally offended then take this apology to be specifically for you. Otherwise, we apologize to Jewish Mexicans, President Barack Hussein Obama Mmm Mmm Mmm a.k.a. Hopey McChangey, Catholic Priests who dork little boys, vegetarians, Fruit Loop, Atkins' Diet adherents and other fat-asses, Dennis J. Olson, Delta Lady, Joe and his Socks, paranoid persona's, space aliens, Illegal Aliens, Boy Scouts, same sex aficionados, Harry Reid, Nancy Pelosi, Canadians, ditch diggers, people who support the aforementioned, people on Prozac, Mel Gibson, Nazi Mods, Tiger Woods, motorcycle gang members, rag heads or towel heads or any other Middle Eastern personas or personae, Crotch Bombers, Britney Spears, the blind, the entire Gay and Lesbian community, Charlie Sheen, Black Panthers, NAACP, and anybody who has ever been called Lard Ass.