It's A Planet: We're Winning!

http://www.newyorker.com/online/blogs/comment/2014/06/many-moons-of-pluto.html

I was working on an acting job this week, and the subject of Pluto's status came up, like it often does when I am part of a conversation. One of the crew members told a story about an incident between her daughter and a kindergarten teacher about six years ago. Following a pre-set curriculum, the teacher taught her class about the solar system, and when they got to Pluto, she told the children that Pluto is a dwarf planet, then added that dwarf planets are not planets but another type of object entirely.

The then-six-year-old daughter immediately recognized the flaw in this statement. "If dwarf planets are not planets, then are dwarf people not people?" she asked her teacher. Stumped, the teacher didn't know what to do, unable to explain her position. That night, she called the girl's mother and told her about the argument she and the girl had had in class. "I didn't know what to say," the teacher said, and it was obvious from her tone that she believed the girl was right.

And she was. A six-year-old inherently recognized that the IAU definition makes no sense. Many adults have asked the same question she did in commenting on various Internet sites. But now we have a kindergartner who knows better than the IAU. That is priceless!

With the New Horizons flyby only one year away, many people, children and adults, are already raising the inevitable question asked in the article above: will the images and data from the mission lead to a reconsideration of Pluto's planet status, whether by the IAU or by some other group or just by public consensus.

The media goofed big time by portraying the IAU vote as a done deal, as if 424 people could just change the status of a celestial body 3 billion miles away. To those of us who never accepted the IAU decision, which was made in a highly flawed process and involved a very questionable definition, Pluto never stopped being a planet. One of the reasons the IAU decision was met with so much outrage is that people inherently understand that science does not work like religion. Something does not become true or stop being true through a decree from "on high." Notably, the IAU leadership was asked by professional astronomers to re-open the discussion in 2009 but adamantly refused, leading those astronomers to boycott that year's General Assembly. As a result, the split between the IAU and astronomers who disagree with them on this and other issues has become much more pronounced, and the IAU has lost a lot of respect in the astronomy community.

Nobody voted on relativity; nobody voted on whether the universe is made of many galaxies or just the Milky Way, and nobody will vote on whether the Big Bang or another theory explains how the universe came to be. Ultimately, detailed study over time is what determines whether theories and ideas rise or fall.

The anti-Pluto activists' claim that opposition to Pluto's demotion is "emotional" is essentially a straw man created to discredit those with whom they disagree. Those of us who support Pluto's planet status do so because we adhere to what Dr. Alan Stern calls a geophysical planet definition. According to this definition, a planet is any non-self-luminous spheroidal body in orbit around a star, in orbit around another planet, or free-floating in space. Yes, this means that spherical moons such as Earth's moon and Europa are satellite planets. The key is that the object in question is large enough and massive enough to be rounded by its own gravity. When this happens, a world becomes complex, often with geology, weather, and layering. Pluto almost certainly has all three, as does Ceres. This is what makes them planets. Ironically, Dr. Stern is the person who first coined the term "dwarf planet," but he did so to designate a third class of planets in addition to terrestrials and jovians, small planets large enough to be rounded by their own gravity but not large enough to gravitationally dominate their orbits. He never intended for dwarf planets to not be considered planets at all. In fact, the concept of dwarf planets being a subclass of planets is very much inline with the use of the term "dwarf" in astronomy, where dwarf stars are still stars, and dwarf galaxies are still galaxies.

Some supporters of Pluto's demotion based their position on the notion that we cannot have too many planets in our solar system. That is hardly a scientific argument. We have whatever number we have, and if that turns out to be 100 or more, so be it. Memorization of a list of names is not important to learning. We don't ask kids to memorize the names of all the rivers or mountains on Earth, just to learn the characteristics that define a river and a mountain.

Pluto is a planet, but it is no longer the outermost planet. That designation possibly belongs to dwarf planets Sedna or Biden, or to a yet undiscovered world. Just recently, astronomers published an article making a case for the presence of two giant planets orbiting far beyond Pluto. It will be interesting to see whether these really exist.