Pluto: The Way Forward

Probably like many of you, I'm growing a bit weary of the Pluto controversy. I was originally planning to drop the discussion from this blog. But before I turn to another topic on Thursday (and I promise I will!), I wanted to point out that I have had several very interesting private discussions this past week with planetary scientists about the Pluto controversy. They have convinced me that the International Astronomical Union (IAU) vote to downgrade Pluto to dwarf-planet status, despite being made by only a few hundred people, was indeed representative of the professional astronomical community as a whole, that it followed established procedures, and that it was based on sound scientific reasoning. I also agree with their contention that the IAU is the only proper forum to address these issues.

But I still think that for a variety of reasons that I have discussed ad nauseum, the IAU definition is flawed on a number of accounts, and it needs to be improved regardless of what one thinks about Pluto's status. And even though several scientists and readers have raised very strong arguments in favor of the IAU's decision to downgrade Pluto, I still have not found any of them to be satisfying from a strictly scientific perspective. I'm comfortable with the IAU's decision that Pluto is a "dwarf planet," but just as a "dwarf star" is still a "star," and a "dwarf galaxy" is still a "galaxy" in conventional astronomical usage, I think the majority of voters at the IAU General Assembly made a scientific and public-relations error by deliberately specifying that a "dwarf planet" is not a "planet."

So, where do we go from here? There is a great deal of acrimony within the astronomical community right now. Scientific debate is healthy and enables human knowledge to advance. But the degree of bitterness and anger that currently exists within the community is probably not a good thing, and goes beyond typical and appropriate standards of scientific debate. I continue to be utterly amazed at the passion that is stirred by a relatively small ice world in the distant reaches of the solar system.

I am going to paraphrase one of the e-mail messages sent me last week, from the distinguished astronomer Keith Noll of the Space Telescope Science Institute. I agree totally that this is the way to move forward. We need a calmer scientific discussion that seeks to broaden the definition of "planet" to include extrasolar planetary systems, that deals explicitly with binary objects in the solar system (dozens of binary asteroids and trans-Neptunian objects are known), and that includes planet-sized satellites such as Ganymede, Titan, and Earth's Moon. (One could make a very strong case that these objects should also be considered "planets," with the appropriate terminology to indicate their dynamical status.) He would also like any broadened definition to address the very interesting issue of free-floating planetary-mass objects that are being found in increasingly large numbers in interstellar space. Dr. Noll concludes, "When that happens, Pluto may make a reappearance as an ice dwarf planet that is still a planet."

Before I close, I want to thank everyone who has written to this blog to express his or her thoughts on the Pluto/planet controversy. I wish I had time to respond individually to everyone's comments and questions. But as you know, we also have a magazine to produce! :-)