Fickle Astronomers Can't Decide Pluto's Fate

It would seem that I spoke too soon last week when I welcomed the prospect of our new planetary neighbors. In a stunning turn-around, the International Astronomers Union reversed their previous position of adding three new planets to our solar system. Instead, the IAU came to the rather difficult decision of stripping Pluto of it's planetary status.

The decision was ultimately driven by technical advances that have allowed us to look deeper into space, and to more accurately determine the sizes of remote objects. "This is all about the advancement of science changing our thinking as we get more information," said Richard Binzel, professor of Planetary Sciences at MIT, and a member of the planet definition committee.

The IAU scientists agreed that, to be called a planet, a celestial body must:

1. Be in orbit around a star while not itself being a star.
2. It must be large enough in mass for its own gravity to pull itself into a nearly spherical shape.
3. It must have gravitationally swept and cleared the immediate neighborhood of its orbit of other debris.

So Pluto failed their third rule due to its orbital overlap with Neptune. Xena, and Ceres also fail this measure. Even now, though, the publishers haven't started warming up the presses yet, because the astronomical smack-down continues.

From yahoo: "Pluto Hijacked in Revolt"
By Paul Rincon
Science reporter, BBC News

A fierce backlash has begun against the decision by astronomers to strip Pluto of its status as a planet.

On Thursday, experts approved a definition of a planet that demoted Pluto to a lesser category of object. But the lead scientist on Nasa's robotic mission to Pluto has lambasted the ruling, calling it "embarrassing". And the chair of the committee set up to oversee agreement on a definition implied that the vote had effectively been "hijacked".

The vote took place at the International Astronomical Union's (IAU) 10-day General Assembly in Prague. The IAU has been the official naming body for astronomy since 1919. Only 424 astronomers who remained in Prague for the last day of the meeting took part.

An initial proposal by the IAU to add three new planets to the Solar System - the asteroid Ceres, Pluto's moon Charon and the distant world known as 2003 UB313 - met with considerable opposition at the meeting. Days of heated debate followed during which four separate proposals were tabled.

Eventually, the scientists adopted historic guidelines that see Pluto relegated to a secondary category of "dwarf planets".

Drawing the line

Dr Alan Stern, who leads the US space agency's New Horizons mission to Pluto and did not vote in Prague, told BBC News: "It's an awful definition; it's sloppy science and it would never pass
peer review - for two reasons.

"Firstly, it is impossible and contrived to put a dividing line between dwarf planets and planets. It's as if we declared people not people for some arbitrary reason, like 'they tend to live in groups'.

"Secondly, the actual definition is even worse, because it's inconsistent."

"One of the three criteria for planethood states that a planet must have "cleared the neighbourhood around its orbit". The largest objects in the Solar System will either aggregate material in their path or fling it out of the way with a gravitational swipe.

Pluto was disqualified because its highly elliptical orbit overlaps with that of Neptune. But Dr Stern pointed out that Earth, Mars, Jupiter and Neptune have also not fully cleared their orbital zones. Earth orbits with 10,000 near-Earth asteroids. Jupiter, meanwhile, is accompanied by
100,000 Trojan asteroids on its orbital path.

"These rocks are all essentially chunks of rubble left over from the formation of the Solar System more than four billion years ago. "If Neptune had cleared its zone, Pluto wouldn't be there," he added.

Stern said like-minded astronomers had begun a petition to get Pluto reinstated. Car bumper stickers compelling motorists to "Honk if Pluto is still a planet" have gone on sale over the internet and e-mails circulating about the decision have been describing the IAU as the "Irrelevant Astronomical Union".

I wonder which Roman gods will triumph?