LAST year, two colleagues and I announced that we had found an unknown body slightly larger than Pluto in the far reaches of our solar system. Since then, astronomical confusion has reigned on Earth and, depending on whom you ask, our solar system has 8, 9, 10 or, shockingly, 53 planets.
In the coming weeks, the International Astronomical Union, which oversees astronomical rules and conventions, will vote on a strict definition of “planet.” The result of that vote is hard to predict, but soon, we’ll likely lose a planet we’ve gotten to know for the past 76 years, or gain at least one more.
From a scientific point of view, the status of Pluto and the newly discovered object — stuck with the cumbersome label 2003 UB313 until astronomers decide what it is — is easy to discern. If you were to look unemotionally at the hundreds of thousands of bodies orbiting the sun, only eight (Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune) would clearly distinguish themselves by their large sizes.
The remaining objects, which are significantly smaller, are mostly either rocky bodies in the asteroid belt between Mars and Jupiter or icy bodies in the Kuiper Belt in the distant regions beyond Neptune. Of the more than 1,000 known objects in the Kuiper Belt, 2003 UB313 and Pluto are the largest and second largest.
So why is there any debate at all, if the scientific view is so clear?
It all dates back to the discovery of Pluto in 1930. At the time, Pluto was thought to be considerably larger than it is now known to be, and the existence of the rest of the Kuiper Belt was unknown. No other reasonable category existed in which to place the object, so Pluto became the oddball planet at the edge of the solar system.
Since then, Pluto has been very much a part of our mental map of the universe. You’ll find it on lunchboxes, postage stamps, NASA Web sites, and in the mnemonics that children learn to remember the planets. Pluto’s qualifications may be more cultural than scientific, but we’ve fully embraced it as a planet in good standing.
This is why astronomers who question Pluto’s status come across as bullies trying to kick everyone’s favorite cosmic underdog out of the club. And while they have a point — after all, it’s not a great idea to let cultural attachments dictate scientific categories — they’re missing an important part of the picture.
Think of it this way. The term “planet” is similar to “continent.” The word helps us organize our world, but the division between continents and subcontinents is thoroughly arbitrary. Yet no union of geologists has tried to vote on a definition of “continent,” and no one is concerned that letting culture determine the difference between Australia, the smallest continent, and Greenland, the largest island, somehow erodes science.
Like continents, planets are defined more by how we think of them than by someone’s after-the-fact pronouncement.
How then should we think about 2003 UB313? I’m biased, but I like to imagine this question through the eyes of the child I was in the 1970’s, when astronauts had just walked on the Moon, the first pictures were coming back from the surface of Mars and the launch of Skylab promised a future of unbroken space exploration.
If I had heard back then about the discovery of something at the edge of the solar system, I wouldn’t have waited for a body of astronomers to tell me what it was. I would have immediately cut out a little disk of white paper and taped it to the poster of planets on my bedroom wall. That night, I would have looked up, straining to see the latest addition to our solar system, hoping that I, too, might someday find a new planet.
Recently, many plans for exploration and scientific study have been scrapped, and those that haven’t are being scaled back. It’s hard to have the same excitement about a limitless future in space.
The astronomical union isn’t helping matters by forcing a Hobson’s choice: stick with the current nine planets or open the floodgates to a yawn-inducing 53 or more. It’s a “No Ice Ball Left Behind” policy.I hope the union takes another galactic approach, and simply declares 2003 UB313 our 10th, full-fledged planet. Doing so might convince schoolchildren to put new paper disks on their walls, to look up to the sky and realize that exploration does continue, and that they can be part of it, too.