What a bum deal for Pluto: Yesterday, it either lost its nifty distinction as the most distant planet in our solar system or it got kicked out of the planet club entirely.
That’s because astronomers have announced the discovery of Sedna, a ball of rock and ice currently about eight billion miles from here–three times further from the sun than remote Pluto and about three quarters as large as its frigid little friend.
We knew this was coming. The search for the tenth planet has been underway ever since Clyde W. Tombaugh spotted Pluto in 1930 and realized it wasn’t moving fast enough to be an asteroid. He was in fact looking for something much bigger–a Planet X that would explain some deviations in the orbit of Neptune. This, in fact, is how Neptune had been discovered in 1846. The German astronomer Johann Galle knew exactly where to look because John Adams of Cambridge and Urbain Leverrier of Paris had predicted its existence based on the irregular behavior of Uranus, the most unfortunately named object in our solar system.
Today, we know that mismeasurements caused the supposed deviations in Neptune’s orbit, not Planet X. But the search for new planets in our solar system continues. Two years ago, a pair of Caltech astronomers located Quaoar, an object about half the diameter of Pluto. Its orbit is nearly circular, which is much more normal than Pluto’s eccentric path around the sun. Sometimes Pluto is briefly closer to the sun than both Neptune and Quaoar and at other times it is further out. (Sedna’s orbit is the strangest of all–it lasts 10,500 years in an ellipse that seems more like a comet’s than a planet’s, with a perihelion of about 8 billion miles and an aphelion of 84 billion miles.)
The discovery of Quaoar highlighted a debate that had erupted some years earlier over whether Pluto was in fact a planet. In the early 1990s, astronomers came to realize that there were a lot of objects zipping around the sun outside the orbit of Neptune in what they called the Kuiper Belt. Many of them began to suggest that Pluto was simply the biggest of these–more “planetoid” than “planet.”
I always found this irritating. First of all, Pluto wins my sympathy as the runt of the litter–it’s dinky, it’s super cold, and I feel sorry for it. Hey astronomers: Does it really pain you that much to let the poor thing be a fully certified planet? Were you mean to small animals as children? Also, there’s a certain aesthetic appeal to a solar system that concludes with miniature Pluto, a tiny flourish after a series of enormous gas giants.
Maybe I’m overreacting. If anybody lived on Pluto, I’d be happy to let them decide: littlest planet or king of the Kuiper Belt? Maybe we should leave it up to the first person who sets foot on Pluto.
Which brings me to my space-policy point. I’m an advocate of spending plenty of federal dollars on space exploration, but I’m also skeptical of sending people to Mars in the near term, as the Bush administration has proposed. Yes, yes, it would be a glorious achievement and I’d love to see someone plant an American flag on top of Olympus Mons. But I also suspect that we could get a bigger bang for our bucks, in terms of raw scientific knowledge about the universe, by investing in unmanned space probes, high-powered telescopes, and the like.
A relentless focus on Mars would force us to crimp on proven technologies already in hand and unproven ones that are within easy reach. NASA’s recent decision to cancel a final servicing mission to the Hubble space telescope is due in part to the Columbia disaster (see NASA head Sean O’Keefe in yesterday’s Houston Chronicle here)–but also a matter of budgets. One of our most important tools for the study of astronomy will suffer for it. Diverting billions to the human exploration of space doesn’t strike me as an obviously better bargain.
The discovery of Sedna shows us how much there is to learn. Besides, I’m still waiting for the first really good picture of Pluto. There’s no reason why we shouldn’t have one soon, though by soon I mean within the next decade or two.
And after that, on to Sedna–or Planet X, if it’s really out there.