Scientists gear up for planetary smackdown

"I'm tired," Tyson said. "I've been arguing Pluto for eight years, so it's another occasion where I'm arguing Pluto. This one happens to be a little more formal in its construct. So I see it as another day of just trying to tell people, teach people about, what we now know about the solar system."

Sykes thinks an object should be considered a planet if it's round and orbits a star, which is a definition based on physical features of an object, such as its size and mass. Objects become round when they are so massive that gravity crushes them into this shape, which is in hydrostatic equilibrium (a state where gravitional and internal pressures are in balance). His definition would usher in not just Pluto, but also Ceres (an object in the asteroid belt) and Eris (the current name for 2003 UB313), as solar system planets.

Based on what has worked in the past for planetary scientists, Tyson supports the idea of using "observational features" to put an object on or off the planet list. Such criteria would include distance from its host star, but it wouldn't include what the planet is made out of. Particularly with planet-like objects discovered outside of the solar system, astronomers can't eke out, say, whether the core is made of iron or another chemical, or whether its surface is rocky or not.

It is hard to know what will transpire at the conference with so many top thinkers, Tyson said.

"When you bring a lot of creative, talented people together new solutions can arise that might not have arisen from any one individual," he told SPACE.com. "The collaboration, the intersection of ideas, has its own way of creating new understanding."

What to expect
Sykes and others organizing the conference say the most important aspect of the conference is, well, the conference itself.

"This topic provides the perfect opportunity to teach science as a process, not a collection of facts," said conference organizer Keith Noll of the Space Telescope Science Institute in Baltimore. "We also need to stress the importance of incorporating new discoveries to continually improve our understanding of the diverse objects within planetary systems."

Hal Weaver, a conference organizer and planetary astronomer at APL said, "No votes will be taken at this conference to put specific objects in or out of the family of planets." He added, "But we will have advocates of the IAU definition and proponents of alternative definitions presenting their cases."

At the end of the day, though, scientists are looking to come up with some sort of consensus on the topic of what it means to be a planet.

"There's a lot of emotion, still a lot of room for opinion," Tyson said, "but it's conferences like this that are hoping to settle the dust and see what remains standing and see if a consensus can emerge."

If a sensible classification system does emerge, Tyson said, it will spread throughout the astronomical community.

The best-case scenario in Tyson's view: "Everyone sings 'Kumbaya' at the end with a brand new classification scheme for everything that orbits a star. That would be really cool."

His worst-case scenario: "Worst case is that people throw tomatoes at each other. There's been some fascinating emotion that has arisen over the past eight years. And I'd be interested to see at what level they express themselves at this conference."

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