Counterpoint: Back to Hades, Pluto

Eminent astrophysicists received unprecedented attention from schoolchildren in 2006. Unfortunately, the attention consisted of an astonishing volume of hate mail.

The International Astronomical Union (IAU) had decided that Pluto was no longer a planet and third graders worldwide were revealing something unsavory about human nature as they attempted to drag science back to what they learned in first grade. Well, surprise, kids. The universe is a big place and we are constantly relearning everything about it. Ignorance is intrinsic to astronomy and planetary science. Don’t get attached to what you learned yesterday, because it will be out of date in two years.

Today’s nostalgia for Pluto’s exalted position in what was then a relatively unexplored cosmos is a distraction from the ongoing torrent of discoveries that constantly recontextualize humanity. Moreover, Pluto’s new position in the solar system is vastly more exciting than its old role as a lonely, cold planet.

Pluto’s demotion is overwhelmingly intuitive to most scientists, although a precise justification remains elusive. People like Hayden Planetarium director Neil deGrasse Tyson and Caltech astronomer Mike Brown have written books explaining the IAU’s infamous decision. In short, the astronomical community pulled a collective all-nighter to agree on a technical definition of “planet” that would exclude Pluto. Historically, planets have been loosely defined as unique objects that dominate the solar system; no precise definition has ever been sufficient to capture planetary diversity while excluding interlopers like Pluto.

The IAU’s attempt, no exception, is clunky (why does a planet need to “clear its orbit”? What does that even mean?), but prevents the nightmarish alternative. Pluto is part of the Kuiper Belt, a population of icy bodies very far from the Sun, some of which are probably larger than Pluto. If Pluto is a planet, then the larger members of the Kuiper and asteroid belts are also planets and the word’s utility has vanished. The eight unique planets deserve individual examination, but Pluto must be considered statistically with its compatriots in the Kuiper Belt.

Exploring Pluto nevertheless remains a national priority. In fact, the $700 million New Horizons mission to Pluto was launched a few months before Pluto’s demotion, with total support from scientists worldwide. New Horizons will classify the surfaces, interiors, and atmospheres of Pluto and Charon (Pluto’s satellite) in 2015 and potentially visit additional Kuiper Belt objects afterwards. Because the Kuiper Belt has been relatively undisturbed for billions of years, it preserves records of interactions with other stars during the solar system’s formation and may offer evidence that our gas giant planets (Neptune, Uranus, Saturn, and Jupiter) have dramatically shifted their orbits. Pluto prototypes a class of objects that reveals much more about our origins than Pluto could on its own.

Pluto’s demotion should remain unmourned. Reinstatement would unnecessarily confuse students and the public. Planetary science is new, exciting, and in a constant state of renewal.

In the last 50 years, planetary exploration has returned an awesome series of discoveries. Robotic spacecraft have visited the eight planets and many other celestial objects. NASA’s Kepler mission may detect an Earth-sized planet orbiting in the so-called habitable zone of a Sun-like star as soon as 2012.

These epic quests have expanded our imagination, hinting that certain questions may have fantastic answers. Does Mars currently harbor subsurface life? Is there an advanced civilization lurking among the twinkling lights of the New Haven sky?

To study planets is to constantly reconsider all assumptions, methods, and conclusions. Pluto’s planethood is a necessary victim of this process.

Joseph O’Rourke is a senior in Silliman College. He is a member of the Yale Drop Team and an Astronomy & Physics and Geology & Geophysics major.


  • laurele

    Pluto’s demotion should not be mourned; it should be overturned. The IAU definition creates a far greater nightmare than and does more to confuse the public than getting rid of it would do. First, it conveys the message that science is decided by fiat of an authoritative body, which is not the case. That is the way of dogma. Things do not change merely because “someone said so,” and it is for this reason that so many people reject Pluto’s demotion. Why would the utility of the word “planet” vanish if there are hundreds of planets in the solar system? We already know, given exoplanet discoveries, that there likely are billions of planets in the universe. No one objects to having billions of stars or billions of galaxies with the claim that this reduces the “utility” of the words star and galaxy. The real paradigm shift here is a change from a solar system of nine planets to one of possibly 50 or more. I am also troubled by the fact that you mention only books written on the side supporting the IAU decision while ignoring those written from the other point of view. Two good books supporting Pluto’s planet status are “Is Pluto A Planet?” by Dr. David Weintraub and “The Case for Pluto” by Alan Boyle. “Pluto Confidential: An Insider Account of the Ongoing Battle Over the Status of Pluto,” is co-written by Dr. Laurence A. Marschall and Dr. Stephen P. Maran, two authors representing opposing sides in this debate. Interestingly, even Tyson has come to admit that the debate over Pluto’s planet status is still ongoing and has gone so far as to say he never claimed our solar system has only 8 planets. It is very disappointing to see the newspaper of a university as prestigious as Yale be so one-sided in discussing what is clearly an ongoing debate. Finally, you do not mention that the demotion was adopted by only four percent of the IAU, most of whom are not planetary scientists and was opposed by an equal number of professional astronomers in a formal petition led by New Horizons Principal Investigator Dr. Alan Stern. Pluto’s planethood is NOT a necessary victim of the scientific process in planetology; it is a victim only of human shortsightedness.

  • Cody

    What an awesome column!