When I was growing up and learning about the planets of our solar system, many children used a mnemonic like the title of this post to remember the order of the planets, finishing it with something like “Pizzas” or “Pies.” It was something we all accepted as part of the natural order of the universe — that we live in a solar system that has nine planets, with us on the third.
But on August 24, 2006, the International Astronomical Union (“IAU”) finally provided a formal definition of a planet and poor Pluto did not make the cut. There are only eight planets that orbit our Sun. Some of the reaction to the change was strongly negative. Petitions were organized online to implore the IAU to reconsider its decision and to reinstate Pluto to its “rightful” place as a planet. Protests were held, with people marching with placards proclaiming that “Size Doesn’t Matter” and wearing T-shirts announcing their “Protest for Pluto.” The State of New Mexico — where Clyde Tombaugh was working when he discovered Pluto in 1930 — passed a resolution declaring that Pluto will always be considered a planet when in the skies of New Mexico. Illinois — where Tombaugh was born — did the same thing a couple of years later. A resolution was introduced in California denouncing the IAU for “scientific heresy.” And many astronomers I know, who remembered with deep fondness how they discovered the sky as children, felt a sentimentally wistful loss at the change. Even now, four years after the IAU decision, protests are still occasionally being held. 
It is heady stuff, whether Pluto is rightfully part of the club of planets or not.
The decision of the IAU is one that emblemizes how brutal science rightfully is as new information and understanding is developed. Old ideas that no longer fit with modern evidence and knowledge are to be summarily executed in favor of concepts that do comport with what we have learned through our investigations into nature. And even though some astronomers felt some nostalgia, they also know that this ruthlessness is a necessary part of the scientific method that they embrace.
I was reminded of Pluto — and of both the strict demand that science has for evidence and its willingness to reject old ideas wholesale — when I read the decision in Perry v. Schwarzenegger, the federal court decision from last week holding that prohibiting same-sex marriages violates both the due-process and equal-protection clauses of the federal Constitution.
One of the strongest reasons for opposition to same-sex marriages is rooted in the traditions of this and other countries that marriages are between one man and one woman. Those traditions very much reflect a moral and often religious view of what marriage is, and a judgment that homosexuality is “wrong.” But as Thomas Jefferson famously noted in his 1802 letter to the Danbury Baptists, the United States seeks to maintain a “wall of separation” between church and state through the First Amendment to the federal Constitution. As the judge in Perry noted, a “state’s interest in an enactment must of course be secular in nature.”
And so the judge — who interestingly had difficulty with his original appointment by Ronald Reagan because he represented the U.S. Olympic Committee in prohibiting use of the term “Gay Olympics” — demanded that there be some evidence that a legitimate state interest is promoted by limiting marriage to opposite-sex couples. Like the IAU and Pluto, it would not be enough that there was a long history of such a limit, and the evidence had to be real and solid.
There are many reasons that have been suggested by those who are opposed to same-sex marriage and that were considered in Perry. The interest of the state in promoting procreation. The commonly held belief that children’s emotional development is most stable when raised in a household with both a father and a mother as role models for each sex. The risk that opening up marriage to same-sex couples will erode its value, even in perception, of providing stability for heterosexual couples. If true and supported by evidence, it is difficult to argue that these are not legitimate interests of the state.
But that is where the proponents of a traditional definition of marriage fell short. Much evidence from social scientists was presented during the trial that these reasons are not supported by evidence — that children develop emotionally with as much strength when raised by same-sex or opposite-sex households and that relaxation of restrictions on the physical characteristics of parties who marry is unlikely to erode the respect that heterosexual couples have for marriage. A strong analogy was made to the 1967 decision of the Supreme Court in Loving v. Virginia that miscegenation laws banning interracial marriage were unconstitutional.
It is widely accepted that the parties wanting to preserve the traditional definition of marriage did a poor job in presenting their case during trial, even as the judge nudged and implored them to do better and to present their case more persuasively. They didn’t call nearly as many witnesses as the other side and the witnesses that they did call were less well-credentialed and credible. There is still a significant belief that some of those interests articulated in support of limiting marriage to opposite-sex couples do actually have evidence among social scientists. And no matter which side one falls on the issue, we should all acknowledge one fundamental fact: the contrary evidence deserves to have been presented in its strongest and most persuasive form. It is when the strongest possible evidence is considered and still found to be lacking — just as the IAU did with Pluto — that we have the greatest confidence in decisions, particularly when they seem to run counter to tradition and intuition.
The full opinion in Perry can be read here.
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