Friday, February 26, 2016

Adventures in the Process of Science, Part Two. Why are so many meteorites carbonaceous chondrites?

One of the best places in the world to find meteorites is Antarctica. When meteorites fall in Antarctica, on top of a thick sheet of ice, they often do so far away from any mountains that might happen to jut up through the ice. So if you find a rock on the ice in Antarctica, it has to be a meteorite, right?

It’s not so simple. There aren’t many rocks out on the open ice. If you find one there, you are in luck, but it is not cost-effective (or safe; every Antarctic expedition is risky) to criss-cross numerous square kilometers of ice in the hopes of finding one. And you need a sample size, not just one rock. Many of the rocks have accumulated in places where the glaciers have rammed up against mountains, and where the dry winds of Antarctica have sublimated the ice away from them. These are the places to go to find the most meteorites. The problem is, there are also some Earth rocks there. So, how do you tell a meteor-right from a meteor-wrong, to use Ira Flatow’s phrase?

It turns out, we are told, that most meteorites are carbonaceous chondrites, which have a characteristic internal structure. So you look for this kind of rock, which an expert can do at a glance, and you have found a meteorite.

You are probably ahead of me on this one. This is circular reasoning. Most meteorites are carbonaceous chondrites because that is the only kind of meteorite you can recognize at a glance in Antarctica. And since you cannot analyze the meteorites in the limited scientific laboratory space in Antarctica, you have to send them back to the States. But this is expensive, so you can’t send every rock; you can only send the ones that are likely to be meteorites—carbonaceous chondrites.

Scientists have done an amazing job analyzing the solar system by studying meteorites. The rest of us just have to be as cautious as they are at interpreting the results.

No comments:

Post a Comment