There appears to be no end to the current controversy over the 2006 demotion of Pluto-from the ninth planet of the solar system since first discovered in 1930-to mangy dwarf planet status.
When a few members of the International Astronomical Union (IAU) met in Prague that year to consider the question, their deliberations created a firestorm among astronomers and planetary scientists; many, notably in the United States, protested loudly that they weren't invited to be part of the discussion. Among the protesters is Alan Stern, principal investigator of NASA's New Horizon probe now past the half way point for a fast flyby of distant Pluto.
A portion of the space science community was upset over how the question was handled-and by most accounts, the Pluto decision was handled badly. Science can be messy and there's nothing messier than the current tug of war over planetary semantics.
At the heart of the storm is the definition of just what a planet should be. To be classified as a plant, must a celestial body be a certain size? Must it have a "traditional" orbit around its sun? Must it be composed of rock or ice (or both)?
According to Internet science writer Robert Roy Britt, "The IAU's final proposal was lambasted by many astronomers for having been slapped together at the last minute and for not adhering to recommendations from two separate committees."
NASA astronomer David Morrison attended the August 2006 IAU meeting and was one of the few Americans in attendance for the final vote demoting Pluto.
"The definition of a planet is not primarily a science issue. Scientists can use all sorts of jargon," Morrison said in a news story last week about the IAU vote. "This issue is of interest because non-scientists, including writers of science textbooks, want a definition. Now they have one. But it is not obvious to me that planetary scientists will adjust their terminology because of the IAU votes."
So, then, dwarf or otherwise, isn't Pluto still a planet?
"Yes and no," Morrison said. "The answer is semantic, based on whether dwarf planets are planets, just as dwarf pines are pines. I would say that Pluto is a planet, but it is a dwarf planet, and the first example of the (new) class of trans-Neptunian dwarf planets. Ultimately, the definition of a planet will come through common usage and scientific utility. There is no need to throw away current school texts; Pluto has not gone away."
In the meantime, according to Alan Stern, the New Horizons primary mission to Pluto hasn't changed. When it arrives at Pluto in July 2015 it will unlock one of the solar system's enduring planetary secrets. The spacecraft will skim the orbits of all eight planets, from Earth to Neptune, and then fly by Pluto and its large moon Charon. Seven science instruments on the probe will shed light on the dwarf planets' geology, interior and atmospheres.
What's in the Sky: During the first week of June in the WNW, in the constellation Leo, Regulus and Mars are close together; use these objects to find several stellar clusters. Mars is moving away from Earth; it will become dimmer as summer passes. Seeing Stars' sky chart is courtesy of J. Kirk Edwards.
Lou Varricchio, M.Sc., lives in Vermont. A former NASA science writer, he is Vermont's NASA/JPL solar system ambassador.