So totally, totally cool.

Labels: art, moon, planetary geology

One of the interesting things I learned about when reading Marcia Bjornerud's Reading the Rocks was about the putting-together of our solar system. The scientific consensus is that our Sun is a second- or third-generation star, with previous iterations having been destroyed through supernovae. (The energy of the supernova is capable of fusing low-atomic-weight elements together into heavier elements.) Post-supernova, a big dispersed cloud of dust and gas existed: the pre-solar nebula. The next phase of history took the nebula and condensed it into a protoplanetary disc, and then that fried-egg-shaped accumulation self-organized (first via static charges attracting particles together -- the dust bunny effect -- and then via gravity). These simple forces brought many small particles of mass together into a smaller number of larger accumulations of mass. For a modern analogue to this process, consider the asteroid 25143 Itokawa, which looks like this:



It is, essentially, a big three-dimensional pile of space rock. I imagine that if you went and kicked it, some boulders would go flying off in all directions. It's a great example of the sorts of objects that we interpret occupying the early solar system. This process is self-amplifying (a positive feedback loop): the more mass you concentrate in a given area, the more gravity it exerts on surrounding masses, which pull towards one another, resulting in more mass, more gravity, more mass, and so on until you have planets. Eventually, if you get a big enough pile of space rock, gravity can condense it, and through warming (via radioactive decay, and potentially frictional heat from continuing impacts), the component elements could self-sort by density. Those with the highest specific gravity could sink down lower, whereas the scummier varieties would "float" up to a higher level.

Bjornerud astutely mentions that this early solar system would have lots of these little planetismals, kind of like those encountered in Antoine de Saint-Exupery's charming book The Little Prince:



Judging from the steam plume from that knee-high volcano, there's clearly some differentiation taking place down below. Now we get to the interesting part. Some asteroids fall to the planet Earth, whereupon we stop calling them asteroids, and start calling them meteorites. These meteorites are examined in great detail for information about our solar system's pre-pubescent years. One of them, the Allende meteorite, fell in the Chihuahua region of Mexico in early 1969:


image from Wikimedia commons

Geochemical analysis of the Allende meteorite by Lee, et al. (1976) showed something weird: the mineral anorthite, a feldspar, had mostly the same elements that anorthite has on Earth (or the moon): aluminum, calcium, silicon, and oxygen. But it also had a decent amount of magnesium. That's odd, because magnesium doesn't fit into anorthite's crystal structure very well at all. What's more, the magnesium in the Allende anorthite was all magnesium-26, not the "usual" magnesium-24. So... What's up with that?

It turns out that you can produce magnesium-26 as the stable daughter product when you break down radioactive aluminum-26. But aluminum-26 has a really short half-life (geologically speaking): only 730,000 years. As Bjornerud puts it, "The fact that a significant amount of aluminum-26 entered the meteorite's anorthite before decaying to magnesium-26 means that fewer than ten half-lives, and probably just a few million years, had passed between the supernova and the time that the anorthite crystals were being smelted out in the new solar refinery."

So that's stunning: the radioactive aluminum-26 was produced through a supernova explosion, and then, less than 5 million years later, a protoplanetary disc had formed and meteorites like Allende were being formed. Wow -- Until I read this passage, I had no idea that this phase of history went by so quickly! 5 million years is not a lot of time when you're talking about events of this magnitude. I was shocked, and I wanted to share this insight here. Are you shocked too?

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References:
Lee, T., D. A. Papanastassiou, and G. J. Wasserburg (1976), Demonstration of 26 Mg excess in Allende and evidence for 26 Al, Geophysical Research Letters, 3(1), 41-44.

Zimmer, Ernst (2002), Using Aluminum-26 as a Clock for Early Solar System Events, Planetary Science Research Discoveries (website). Downloaded on December 16, 2009.

Labels: analogies, astronomy, books, isotopes, meteors, minerals, planetary geology

Check out Phobos and Deimos sailing across the void. (From here)

Labels: mars, planetary geology, satellite imagery

Wow. You've got to check out these amazing new images from Saturn.

Yet another tip o' the hat to Diego H. for passing this link on to me...

Labels: astronomy, planetary geology, satellite imagery

Every now and again, I like to post an image that just speaks volumes. Check this one out, of Saturn's moon Enceladus. Wow! What a beauty. This photograph was taken on Monday by the Cassini spacecraft. Enceladus may host liquid water below the surface, since it has geyser-like features near its south pole. There are only three places beyond the asteroid belt where eruptions have been seen: Enceladus, the jovian moon Io, and Neptune's moon Triton. Enceladus is only a few hundred miles wide; These fractures are about 1000 feet deep.

Labels: art, planetary geology

Mars has a new robot geologist on its surface, as of last night at just before 8pm (E.S.T.). The Mars Phoenix lander arrived in Mars' north polar region after an apparently dicey landing sequence that went off without a hitch. It unfurled its solar panels and started taking pictures, like the one at the left. That's a new view of the planet thought most likely to give us insights into the possibility of life elsewhere in the universe.

Why the pole? That's where the water is. Remote sensing indicates ice just a few inches below the surface in this area, and the geomorphology seems to back that up. Visible even in this earliest photo, polygonal shaped features suggest repeated freeze-thaw action. (Similar freze-thaw action in Earth's polar regions produces similar features, like these:



That's the way geology works, right? The principle of uniformity suggests that uniform physical laws operating over vast ranges of time and space will produce similar phenomena in different locations. It remains to be seen how valid this principle is in guiding our exploration of other planets, but with Mars it appears that there are some real similarities. And why do we care where the water is? Because on Earth, all life needs water. Figuring out whether life exists elsewhere in the universe has huge implications for our place in the cosmos.

Labels: mars, planetary geology, satellite imagery, tech

Check out yesterday's excellent post by Geotripper about the recent arrival at Earth of light from a supernova that happened 7.5 billion years ago.

Labels: blogs, planetary geology

So, this is weird: a new insight into the planet Mercury is that it has a big long tail which extends away from the planet, strung outwards by the solar wind (a stream of charged particles shooting away from the Sun in every direction). Comet tails are also due to the solar wind's erosive effect, vaporizing particles & dragging them "down-stream" (i.e., away from the Sun). The tail is long: At 1.6-million miles in length, the streamer of sodium atoms is more than 100 times the planet's radius. Read more here.

Labels: news, planetary geology

I was struck by the visual similarity of these two round graphics from the Science section of today's Washington Post. The first shows the circuitous path taken by the Mercury Messenger spacecraft, which is scheduled to fly by the innermost planet in about 2 hours from the time I'm writing this:


The second image shows the changing ice situation in Antarctica on a cool combination of ice-flow velocity map and ice loss/gain bar graph, wrapped around the edge:

Labels: art, global warming, planetary geology