One of the nicest things about science is that, usually, when you’re wrong you’re just wrong. There is no use sitting around arguing about it or trying to persuade someone to change his mind, you’re just plain wrong and the universe has explained it to you. Game over. Thanks for playing. Try again later. Next?
Only there really was no “next.” Red? For the most part, colors of objects in the Kuiper belt are relatively mysterious, so there wasn’t much of story there. Snow White remained nicknamed Snow White, despite the now obvious inappropriateness of the name, but it mostly became known as a moderately large object in the Kuiper belt that didn’t have a real name. As I mused in this space 2 1/2 years ago, Snow White needed a bailout. By which I meant, we needed to find out something interesting about it or it was never going to be worth talking about, much less naming. As I said back then, "Snow white? Well, it’s just a big Kuiper belt object."
And then something really interesting happened: Snow White got brighter. While observing a slew of Kuiper belt objects at the Keck observatory two years ago, we swung the telescope around to Snow White and were shocked to find out that it was almost two times brighter than we had expected.
Kuiper belt objects don’t suddenly get brighter without a cause (in fact, nothing in the Kuiper belt ever had gotten brighter before). Was it like a giant comet that had suddenly gone into outburst? If so, it would have been – by a large margin – the most distant active comet ever seen and – by a larger margin – the largest. What if, instead, something happened on the surface? A frost formed which reflected more sunlight? Nothing like that had ever been seen before, and it didn’t make a lot of scientific sense, but we have found stranger things. What if, instead, a huge impact on Snow White dispersed a cloud of dust that was reflecting extra sunlight? That would be a shock with Snow White so far in the outer reaches of the solar system where there is almost nothing else around. So what could be going on?
Having the chance to discover something truly exciting like this is one of the reasons that being an astronomer is so much fun. You’re presented with something that doesn’t make sense at all and suddenly you have to figure it out from scratch. No running to Wikipedia to look it up. No asking someone else. It’s just you and the universe staring each other in the eye and seeing who will blink first. And, in my decades in the field, I have found that the most likely explanation to a truly exciting and unexplainable observation is that it’s just wrong. Which, in this case, it was. The universe refused to blink.
In this case the answer wasn’t that our Keck observations were in error, but that Snow White had actually been bright all along, and we just hadn’t realized it from the discovery observations. When you’re out searching vast areas of the sky night after night looking for objects in the Kuiper belt, you observe in all kinds of conditions and all kinds of weather. If you waited just for the times when everything was perfect you would cover much less sky find many fewer things and have a lot less fun. On the night when Snow White was discovered, conditions were relatively poor, so it was impossible to measure precisely how bright the newly discovered object was. We had to make an estimate, like we had had to do many time before. Our estimates had always been within about 30% of the correct value. This time, though, because of the conditions and the location in the sky, our estimate was off by a but more. Even these miss estimates usually don’t matter, as we do follow-up observations later (to track the object to find its orbit) which usually give a much better estimate of the brightness. In the case of Snow White we did the follow-up observations, but conditions even then were bad enough that we never got a better brightness estimate. By the time we got to the Keck telescope, a year had passed, and we had still never gotten a precise brightness measurement, so we were startled at how bright the thing really was. Going back to try to re-calibrate the old data, though, we can see that it was likely that bright all along.
We suddenly realized that Snow White was not just a moderately bright moderately interesting Kuiper belt object, but was actually the 5th intrinsically brightest object known (by which I mean: if you put all of the objects the same distance away from us, Snow White would be 5th brightest, after Eris, Pluto, Makemake, Haumea, and Sedna).
Snow White was looking more and more interesting. The next step would be to obtain a high-quality infrared spectrum of the sunlight reflecting off the surface. Such a spectrum might be able to tell us what was on the surface and thus why Snow White was so bright and why it was so red. We had been doing that sort of spectroscopy of faint objects in the outer solar system for most of the past ten years using an instrument called NIRC (which cleverly stands for near-infrared camera) on the Keck telescope. NIRC was the best Kuiper belt spectrograph in the world, and it had helped with a decade-full of discoveries (ammonia on Charon, the Haumea collisional family, the unusual surface of Makemake, among others), but it had just been retired after 15 years of heavy rotation at the summit of Mauna Kea.
After a decade of having the best window into the surfaces of Kuiper belt objects, the shades were suddenly closed and we were blind. Snow White became not just the largest object in the Kuiper belt with no name, it also became the largest object in the Kuiper belt whose surface was – and seemed destined to remain – a mystery.
Go on to Part 3.
Go on to Part 3.