How I Killed Pluto and Why It Had It Coming - Mike Brown [45]
As we had with Quaoar before, we eagerly looked for pictures of Dutch that had been inadvertently taken by previous astronomers. Dutch was much fainter than Quaoar had been, so there weren’t nearly as many on which it showed up, but after a few days of careful searching we found it back a few years, which was enough to calculate what sort of orbit it had.
What was it going to look like? Circular, the way the orbits of massive planets should be? Scattered, like the orbits of many of the other smaller objects in the Kuiper belt? At first it was hard to tell. Although it is true that you need to figure out only where an object is and how fast it is moving to know an orbit, Dutch was so far away and moving so slowly that every time we measured it we came up with a slightly different answer. First we thought its orbit was circular; then we thought it was moving in a straight line and not even in orbit around the sun (that would be a first!). But after more care and measurement, we finally got the answer: Dutch was definitely not moving in a circular orbit, and it was definitely not moving in a straight line. The orbit was extremely elongated. So was Dutch at its farthest point in its orbit and moving inward like a normal scattered object would? No: just the opposite. It turned out that Dutch was at almost its closest point and moving outward. And its orbit around the sun appeared so elongated that it was going to take eleven thousand years to go all the way out and come back in again. It was the most distant object that humans had ever seen in the solar system, but it was eventually going to be even ten times farther away. Nothing was supposed to act like this in the solar system. It was neither a normal-seeming planet nor a normal scattered Kuiper belt object. There was nothing like it known anywhere else in the universe.
It’s sometimes hard to picture all of these orbits and what they mean. So try this. Take a sheet of copy paper, a pencil, and a quarter (or just follow along on the diagram on the next page). Put the quarter in the middle of the paper, trace its outline, and put a little dot at the center of the circle you have just drawn. This little dot is the position of the sun, while the outline of the quarter is the nice circular orbit of Neptune. Inside this circle is everything in the solar system that was known until the moment that Pluto was discovered in 1930. If you would like to put Pluto on your drawing, put your pencil at the four o’clock position of the circle of Neptune’s orbit and now draw an oval that starts and ends there, but while it goes all the way around the sun it reaches a distance almost but not quite twice the diameter of Neptune’s circle from the sun at the ten o’clock position (okay, if you’re being precise, get out your ruler and make Pluto go 19/16 inches from the center of your circle). Now you can draw the outer edge of the Kuiper belt: Sketch a rough circle all the way around the sun at the farthest distance of Pluto. Finally, shade in all of the space between Neptune and this outer circle. Now it is time to add a few scattered objects. Place your pencil at, say, a point halfway inside your Kuiper belt at the eight o’clock position. Now draw an oval all the way around the sun that starts and ends here but gets to a distance two or three times farther by the two o’clock position. Feel free to draw as many scattered objects as you like, just always make sure to start and end in the middle of the Kuiper belt before zipping off to the edges of the solar system.
Now you will need to draw Dutch. Draw a little dot about three times as far from the sun as the orbit of Neptune at, say, the