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A sample size of 1 August 25, 2010

Posted by Simon in Uncategorized.
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Today’s class at UQ got me to thinking about how probabilities play a role in the ALH84001 meteorite controversy. One thing that stuck in my mind was that there’s only *one* meteorite that people are arguing about.

What if there were two (or more) Martian meteorites that showed signs that could be biological in origin? It seems to me that might swing the argument in favour of those who say there had been life on Mars – it wouldn’t clinch the argument, but I think it makes it stronger.

But what if we find more and more Martian meteorites and none of them show anything like the signs in ALH84001? Then it becomes much harder to argue the case for life on Mars.

So it’s worth reviewing what we already know about Martian meteorites other than ALH84001. Here’s a quick primer:

The Meteoritical Society has a database of all known meteorites discovered on the earth; there are nearly 40,000 confirmed findings, with 92 of them being classified as coming from Mars*. When you account for meteorites that were found close together and appear to have come from the same rock, the number of unique finds drops to 34. Northwest Africa (Morocco, Algeria, Libya) and Antarctica seem to be the hot places for finding the meteorites.

Even though there are 34 Martian meteorites, ALH84001 seems to be unique. One initial analysis of ALH84001 described it as “a new, and unusual SNC (Martian) meteorite”. It’s extreme age – estimated at 4.1 billion years – means that it would have formed when Mars had liquid water, which makes the biological arguments more interesting.

What struck me about the database of Martian meteorites was the year in which they were discovered – almost all of them were found in the last 10 years. This suggests that there will many more discoveries to come, and if more are found that are similar to ALH84001, then the probabilities at play in the Martian life controversy could shift one way or the other.

*How do we know that a meteorite came from Mars, and not somewhere else in the solar system? Chemical analysis of the rock and the gases trapped inside reveals almost identical results to studies of the rocks and atmosphere of Mars. On this point, at least, there doesn’t seem to be much controversy.

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