Geology Liveblog: The MESS

aka Meteorites and the Early Solar System, but that acronym is, uh, fitting.

Astronomers and planetary scientists (and geochemists, to an extent), are interested in a lot of questions about the early solar system. Why did the sun form? Why are there planets? What modern stuff can we use to learn about the early solar system.

From observations of other solar systems, we've got a rough timeline of what order things happened.

1. Once upon a time, there was a cloud of-- stuff.
2. The stuff became gravitationally unstable (possibly set off by a nearby supernova), and collapsed into the protostar and a planetary disk. Most of the stuff ended up in the protostar. Most of the stuff is pretty hot.
3. The protostar starts heating up and becoming an actual star. At the same time, stuff in the disk starts cooling, and the hot gasses start condensing into solids. Stuff like tungsten and calcium condense first, followed by other metals. (A lot of the more volatile things like oxygen and nitrogen don't condense, and don't get acrreted.) This solid stuff starts accreting into asteroids and planets.

Now, let's say you're a geochemist, and you care about what the elemental composition of the solar system is/was. There are two ways you can do that: you can look at the sun, or you can look at meteorites.

The sun's photosphere gives off light. Different elements give off distinctive wavelengths of light. So by looking at the light given off, scientists can calculate the abundance of different elements in the sun. It's overall mostly hydrogen, with a fair amount of helium. It's got a weirdly high amount of iron considering iron's mass (because iron-56 is weirdly stable), higher abundances of stuff with an even number of protons than odd, and very little lithium, beryllium, or boron (because stars kinda... destroy those. It's a thing.) (As a note, the sun is only producing helium. All the other heavier stuff just came along for the ride when the sun formed, and originated in much heavier and older stars.) The sun has the advantage of being almost definitionally made up of the average solar system composition, because most of the solar system is the sun. But, the sun is a little bit enriched in volatile (low boiling/melting point) elements, which skews things a bit. More frustratingly, the estimates for low abundance things are pretty bad using the photosphere method.

However, geochemists are pretty good at accurately measuring things in low abundance-- if they're rocks. Which is where meteorites come in. Meteorites are so useful*! They door-delivery for bits of different celestial bodies. Want to look at a piece of the moon, without going to the moon? Meteorites have got you covered. Want to look at the solar photosphere in more detail? Have CI chondrites got a deal for you! All that good average solar system abundance, easier to measure, and with less of those pesky volatiles! Want to date some of the processes involved in the solar systems formation? Meteorites can help! A bit**!

Yay for meteorites.

*While technically the Earth is more accessible/common than most meteorites, it's much larger and it's more differentiated. Which means that while the whole Earth's composition is pretty similar to various types of meteorites, we can really look at/measure the whole earth's composition, because a bunch of it is in the core where we can't get it.

**Some processes, like condensation, or differentiation, can be dated. Ot her things like accretion or collisions can't be, because they don't leave a chemical or isotopic trace

[Programming note: This may be one of the last Geology Liveblogs, at least for awhile. The start of semester is barrelling towards me, and I'm going to have to focus on new geology rather than revising old geology.]