The Other Side of Pluto
Saturday January 31, 2009
The other day, I mentioned Neil DeGrasse Tyson's appearance on The Daily Show. Shortly thereafter, I was drawn into the debate ... not by a hate letter from a third grader, but by an articulate letter from amateur astronomer Laurel Kornfeld. In the letter, she discusses her views on why Pluto is, in fact, a planet. I quote her e-mail below, where she lists reasons for her objection to the reclassification of Pluto:
- Pluto as a planet is not in a category of one. There are several of these smaller planets that need to be distinguished from asteroids because their makeup is exactly like that of planets in that they are in a state of hydrostatic equilibrium. This means they have enough self gravity to pull themselves into a round shape, which makes them
geologically differentiated like the larger planets and unlike shapeless asteroids and comets. Tyson never discusses hydrostatic equilibrium and blurs this crucial distinction by lumping Pluto and other small Kuiper Belt planets with comets and asteroids.
Editor's Note: My understanding is that Pluto is classified as a "dwarf planet," which is a designation that is distinct from the classification given to comets and asteroids. Hydrostatic equilibrium is specifically defined as one of the key traits in the official dwarf planet definition passed by the International Astronomical Union in 2006. Having not read DeGrasse Tyson's The Pluto Files, maybe there is a point where he equates them with comets and asteroids, but the official classification seems to make them clearly different objects.
- The scientific community has not made a final decision on this matter. This definition was adopted by only four percent of the IAU, most of whom are not planetary scientists. No absentee voting was allowed. It was done so in a highly controversial process that
violated the IAU’s own bylaws, and it was immediately opposed by a petition of 300 professional astronomers led by Dr. Alan Stern, Principal Investigator of New Horizons, saying they will not use the new definition, which they described accurately as “sloppy.”
Also significant is the fact that many planetary scientists are not IAU members and therefore had no say in this matter at all.
Many believe we should keep the term planet broad to encompass any non-self-luminous spheroidal object orbiting a star. - Support for Pluto's planethood is not limited to Americans. I have personally received emails from around the world opposing Pluto's demotion, and there are Internet groups worldwide committed to seeing Pluto reinstated. Many songs and poems opposing the demotion were written by people other than Americans.
- Tyson's claim that people's emotional attachment to Pluto is largely due to the Disney dog is at best questionable. Most Pluto supporters are astronomy enthusiasts with a strong interest in the solar system. They view the solar system as a "family," and see a round object that looks exactly like a planet and find it bizarre that anyone would categorize it as something else.
Editor's Note: My only emotional attachment to Pluto is largely due to the Disney dog.
- Tyson's comparison of Pluto with comets is a red herring. Yes, if brought into Earth's orbit, Pluto would begin sublimating and appear to grow a tail. However, so would any planet brought close enough to its parent star. If Earth were placed in Mercury's orbit, it would appear to grow a tail as well. Pluto is also far larger than any comet, and its orbit never takes it into the inner solar system. Significantly, a large exoplanet was just discovered, which is several times the mass of Jupiter and orbits its star in only a few days, yet has a comet like orbit. Is this object, which is bigger than any in our solar system, not a planet but a comet because of its elliptical orbit? Clearly, "comet-like" orbits alone do not make objects comets instead of planets.
What's your opinion on the status of Pluto? Is it a planet or not? Why? Leave a comment and let us know what you're thinking.
Comments
Bear with me. This will start strange, but will get to the point quickly.
On the first season of Gilligan’s Island, the theme song ended with “and the rest,” not naming the Professor and Mary Ann explicitly. In subsequent seasons, they were elevated to Theme Song status, as they should have been from the beginning.
So we can keep arguing about whether some planets should be part of “and the rest,” or do the right thing and give Pluto the credit it deserves. The other objects out there can be “and the rest.”
Pluto (more correctly, Pluto-Charon) is clearly an outlier in comparison to the traditional planets. I’m quite happy thinking of it as merely the first of the transneptunian objects, or “outsteroids.” But every body with a round shape has some degree of “planetness” from a geologist’s viewpoint.