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Astronomers should apologize for abusing Pluto

It’s pretty difficult to pass a college class if one doesn’t buy the textbook. So, I’m sort of proud of my “C” in astronomy, a grade that averaged the “A” on my term paper with the “F” that I actually earned in the class. I took the class only because I was required to complete a certain number of units in physical and biological sciences in order to complete my first degree, an Associate in Arts from Foothill College in the West Bay Area.

Now, as is the case in so many areas, I wish that I had paid attention to the lectures and done the reading. But, in the days of my squandered youth, the only heavenly bodies that interested me were named Loni, Sandy, Cathy, and Marilyn. During my freshman and sophomore years, the college campus was simply a magnificent datescape. What happened in space was inconsequential. But, it shouldn’t have been. The Soviet Union had launched Sputnik while I was still in high school, and Yuri Gagarin, a Russian cosmonaut, rode the Vostok 1 into space while I was cutting class and trying to arrange a date for some upcoming event.

I suppose I became more interested in things astronomical when an American, John Glenn, achieved orbital flight in the Mercury-Atlas 6 in 1962. But, by that time, I was “between” colleges and working as the assistant manager of the Foothill College Bookstore. My knowledge of the cosmos only extended to my ability to name the nine planets: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, and Pluto. Actually, I learned that in elementary school, not in college. But, that astronomical factoid remained true throughout the 20th century. Then, in 2006, my mental image of the solar system was shattered.

The ecliptic plane

Scientists demoted Pluto from its status as a planet. Why did they do that to the outermost orb, kind of like our little sister, after which Mickey Mouse named his dog?

For the past decade, Pluto has been considered to be a “dwarf planet,” which really isn’t a planet in the same sense as the eight that remained in the major leagues. Some astronomers hastened to point out that, among other factors, Pluto did not share the ecliptic plane with the Big Eight. In order for me to understand this, I had to go back and study the subject that I had abused during my early college years.

Here’s a simple way to understand this concept, which — by the way — is the only way that I understand most things that are outside my own academic field. Imagine a line that follows the earth on its trip around the sun. Now, think of that circle-like image being the rim of an oval-shaped saucer. That is the plane of the earth’s orbit. Now, think about that saucer expanding infinitely, that is the ecliptic plane. The orbits of seven planets are on that same plane (or saucer), more or less. Mercury’s orbit is actually a bit off. Its little saucer would be at a slight angle (about 7 degrees) to the big saucer, and this is known as its inclination to the ecliptic plane.

Pluto, like the Big Eight, revolves around the sun, but its orbit is at a 17-degree inclination to the ecliptic. And, to some eyes, that made it a rogue. But, according to Evan Gough, writing in Universe Today, “Pluto’s status as a non-planet may be coming to an end.” The heavenly body, whose presence was detected as early as 1915 but which was not officially discovered until 1930, has been going through an existential crisis.

What is a planet?

In 2005, another dwarf planet, Eris, was discovered, but it is 27 percent more massive than Pluto. Gough says that this caused the International Astronomical Union (IAU) to look into how planets should be defined. The members had to make a decision: Either expand the definition of what is and what is not a planet or shrink the definition. In the first scenario, Eris and Ceres (among others) would become planets. In the second, Pluto and all other similar bodies would remain dwarf planets or would be given some other designation.

Writing for CNET, Eric Mack claims that there is a “semantics debate that is simultaneously meaningless and central to how we view the universe.” Consequently, most of the members of IAU have “moved on,” sticking with the recognition of eight planets in the solar system. Still, Jean-Luc Margot, chair of the Planetary and Space Sciences Department at UCLA, says that there are a few people, “primarily and perhaps not coincidentally associated with the New Horizons mission to Pluto, who apparently cannot accept a universe where Pluto is not classified as a planet.”

The group to which Margot refers seems to be headed by Kirby Runyon, a doctoral candidate at Johns Hopkins University. Maintaining a philosophy that “nomenclature is important as it affects how we compare, think, and communicate about objects in nature,” his group has developed a new definition.

In a paper that was delivered at last week’s Lunar and Planetary Science Conference, his team proposed: “A planet is a sub-stellar mass body that has never undergone nuclear fusion and that has enough gravitation to be round due to hydrostatic equilibrium regardless of its orbital parameters.” In other words, it’s smaller than the sun, didn’t disintegrate into space dust, is spherical, and revolves around the sun, but not necessarily on the same ecliptic plane as the Big Eight.

Given this new definition, there are more than 110 celestial bodies that could be called planets. Gough points out that “there are sound reasons for updating definitions based on our growing knowledge.” I agree, but I can’t imagine asking elementary school children to memorize the names and order of so many orbs. I’d opt for the designation “classical planets” for the nine (including Pluto) that were known to us through the 20th century. Of course, that classification should be accompanied by an apology from the astronomers who have abused poor, little Pluto.

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