How I Killed Pluto and Why It Had It Coming - Mike Brown [44]
I gave my normal lecture. But at the end I couldn’t resist. After I told my students all about what we understood to be the edge of the solar system, I stopped, looked up, and added, “Maybe.” I told them that I had perhaps just found something that had changed all of that. But I wasn’t sure. And I would keep them posted.
I went back to my office and sent an e-mail to Chad and David. I tried to downplay the potential discovery:
Subject: amusement
I just found something that, if real, is at 100 AU. Wouldn’t that be fun?
Something at 100 AU—a hundred times the distance from the earth to the sun—would be more than three times the distance of Pluto and well beyond anything ever found in the Kuiper belt. Chad wrote back almost immediately:
If that one is real I’ll be buying the champagne.
Chad and I eventually drank that champagne. We were sitting on a beach on the Big Island of Hawaii, with the sun setting over the ocean in front of us, a pig roasting in a pit behind us. By entirely appropriate chance, Antonin, who had convinced me not to quit my search for a new planet, was there, too. We raised our plastic cups to an unending solar system.
• • •
This was it; something so far away that we could nonetheless see had to be big—almost certainly bigger than Pluto. It’s true we had been fooled by Quaoar at first—since it had had a much shinier surface than we had anticipated and was thus unusually bright without being as large as Pluto—but even if this new object had a surface as shiny as Quaoar, it would still have to be bigger than Pluto. Because it had been so elusive, we gave this new object the code name Flying Dutchman. The Flying Dutchman is, of course, the ghost ship of folklore that can never go home and is instead destined to sail the seas forever. We had no idea at the time what an appropriate name this was.
Since the Flying Dutchman—or Dutch, for short—was farther away than anything anyone had ever seen before, it certainly seemed to be part of a new, previously undiscovered part of the solar system. But I knew that there was another possibility. Even though Dutch was currently far beyond the Kuiper belt, it could still really be part of it. Sometimes objects in the Kuiper belt come a little too close to Neptune and get flung out onto long, looping orbits.
We do the same sort of flinging whenever we want a spacecraft to get somewhere in a hurry; we send it by Jupiter first to get a slingshot off the planet. The trick is to aim the spacecraft almost at Jupiter. The spacecraft gets closer and closer to Jupiter and is pulled faster and faster by the gravity of the giant planet, and then it just misses, skims the clouds, and now zips along at high speed toward its final destination. Jupiter is so massive that it has enough gravity to give an object a slingshot that will take it clear out of the solar system. The Pioneer and Voyager spacecraft went past Jupiter, took pictures, got the slingshot, and will never be seen again. Neptune, however, is too small to give a strong enough slingshot to propel something out of the solar system, so when it tries, the objects always come back. Many objects in the Kuiper belt thus have orbits that take them close to the orbit of Neptune but then much, much farther away from the sun. These objects have been called “scattered” Kuiper belt objects, as Neptune appears to have scattered them to those looping orbits.
Only small things get scattered. The large planets are on nice circular orbits because there is nothing big enough to kick them around. The objects in the Kuiper belt—including Pluto—have tilted, elongated orbits because they are too small to resist the bullying