Clyde Tombaugh and Pluto

Much has been said and written over the past several years about the downgrading of the planet Pluto from its position as the ninth planet in our solar system to what is now called a “dwarf planet.”  In other words, it just didn’t quite make the grade as a planet.  Astronomers like planets that do predictable and sedate things, like orbiting the sun in a nice, almost circular orbit, and sweeping the area around them clear of debris.  Pluto just didn’t do that.  It’s so small, almost a small as the Earth’s moon, and it orbits the sun in a weird ellipse that actually crosses over the orbit of the next planet inside it, Neptune.  This frustrated classic astronomers and they reacted by downgrading Pluto to dwarf status.

That really upset the friends and relatives of the person who discovered Pluto in the first place, Clyde Tombaugh (1907-1997).  How could they do that, they wail.  How can you call a planet a planet one minute, and then pull the proverbial rug out from under it the next?  Well, I have to say I agree with the astronomers on this, although I do sympathize with Tombaugh’s supporters.  Here’s why.

This downgrading of Pluto shouldn’t be looked on as a demotion of Tombaugh, nor as a denigration of his work, nor as a minimizing of his contribution to science and astronomy, it should be thought of in a whole new sense.  Tombaugh is still a great astronomer, still deserving of all the accolades he accumulated.  His work still stands alone.  After all, he discovered Pluto in 1930, when astronomers had far fewer instruments to help them in their sky searches.   He knew what he was doing.  The discovery of Pluto wasn’t an accident; he didn’t find it while he was doing something else.  He knew exactly where to look in the sky because he calculated where it should be based on its gravitational effects on the planet Neptune.  He spent hundreds of hours looking at photographic plates of the sky, comparing one with another to see if anything changed from one night to the next.  And he honed in on it like a cat on a mouse.  (Okay, bad analogy, but you get the point.)

All of this actually increases Tombaugh’s status in astronomy, not decreases it.  Yes, I said increases.  The reason is, he discovered, not a planet–and here is why I agree with the astronomers–but the first of a whole collection of objects that orbit our sun way out beyond Neptune and even beyond Pluto, called Kuiper belt objects.  There are thousands, probably even millions of them out there, most so small they can’t be detected very easily.  Pluto is the largest, and it’s so close in (relatively speaking) it could be discovered and tracked.   Many comets that enter our solar system come from this belt; Halley’s comet is probably a Kuiper belt object because it swings in around the sun then travels back to the belt.  That’s why it takes so long from one appearance to the next.  This was a great accomplishment for an astronomer working in the 1930’s and we shouldn’t be lightly tossing it away.  Kudos to Tombaugh.  But we who are inheritors of his legacy need to see him in the correct light.

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