Meteorites in Washington

I am at the Carnegie Institution of Washington this week, working on my research. There is a class of meteorites called carbonaceous chondrites, and what distinguishes them is that they are older than the earth and essentially have the same composition as the sun (except for hydrogen and helium.) You have to think about that a little bit. They can be thought of as frozen globs of the stuff from which the solar system was formed. Now they also contained some short-lived radionuclides form the supernova that apparently triggered the collapse of the gas/dust cloud that formed the solar system. Some of these dust particles acquired an organic mantle during the millions or perhaps billions of years that they spent in interstellar space. The particles also probably had ice on them.

Anyhow, the gas and dust coalesced into planetesimals, and the decay of the radioactive elements heated the planetesimals into a hot mud. Most of the water boiled away, but before it did, it reacted with the silicate dust grains to form hydrated silicates and carbonates. But most intriguingly, these planetesimals had a fair amount of organic chemicals on them, including amino acids. Later, the planetesimals broke up, and pieces of them landed on earth, most notably near Murchison, Australia around 1969 or so. These fragments had probably been floating in space for over 4 billion years.

I am studying the oxygen isotopic composition of the Murchison organic materials to see whether they were synthesized in the hot mud of the planetesimal, or whether the isotopic signature reflects an interstellar origin. Just how oxygen isotopes will tell you that gets rather arcane. My advisor (Bob Clayton) basically invented this field, and I learned it from him. Why we would want to know this, other than it's cool to think that amino acids may pre-date the earth, is also arcane. But with a little JD and a clock rolling over into single digits, I'm sure I could make it clear.

So there. That's my answer to the longstanding question "Just what the hell is he doing?" You may refer inquiries to this post.

Here in Washington, I am working with George Cody and Conel Alexander. Conel has organic residue from Murchison, and I am stripping away the oxygen atoms that might have exchanged with the planetesimal's water. That would leave only the oxygen that might have formed in interstellar space. I will extract the oxygen from the stripped residue and measure the ratios of the various oxygen isotopes. The result? Either it will look like planetesimal water, or it will look like something else. The something else would become grist for the imagination.