Meteorite Monday: Chondrules

One of the great things about taking my meteorites course this term is that I’m learning a lot about the different aspects of meteorite studies and how it all ties into what we know about the origin of the solar system. It’s also giving me the opportunity to revisit previous Meteorite Monday posts and flesh out some concepts that were, at that time, beyond my comprehension.

One of the more well-studied aspects of meteorite research is the chondrule. These are one of the most telling aspects of a meteorite. In the simplest of terms, they are silicate spheres that are usually less than 1 mm in diameter and are found embedded in most ordinary chondrites.

Chondrules that have been separated from their meteorite parent body. (Image from MERGE)

For the purpose of this post I’m not going to get into chondrule formation as it’s a fairly involving topic and is deserving of more time than what I can give it. The important thing to know is that they’re considered some of the oldest material in the solar system. Isotopic dating tells us that they formed within the first 2 to 3 million years of the birth of the solar system. They were little molten droplets that were formed in the solar nebula and were heated to about 1900 C and then experienced rapid cooling. This high heat and quick cooling determined their texture and over all chemical components. They’re generally composed of either olivine or pyroxene and sometimes both minerals occur in the same chondrule.

These minerals can display some really beautiful textures. This is a picture of a chondrule with a barred olivine texture. The olivine crystals are the elongated structures and they’re set in a glassy matrix or body. I highly recommend clicking through the link as NAU has some spectacular pictures of other chondrule types and how they form.

Image from the Northern Arizona University Meteorite Laboratory

This next image is of a chondrule displaying a porphyritic texture. This is a way of describing a course grained chondrule where the olivine crystals are enclosed in pyroxene crystals.

Image from Meteorite Pages (click through for the link to the source page)

And this is one of my favorite chondrule images. These are two chondrules that collided while still molten in the solar nebula and fused together in a quick cooling process.

These two chondrules display a microcrystaline texture. (Image from Meteorite Pages. Click through for the link to the source page).

As I said earlier, there is a lot more behind chondrules and their formation that I can’t get into yet. At some point in the near future I plan on putting together a post that deals with what chondrules tell us about the early years of our solar system.

Meteorite Monday: Link O’ Meteorite News Edition

The latest Martian meteorite to be added to the collection of rocks from Mars. (Photo from Laurence Garvie. ASU News)

Today’s Meteorite Monday is going to be a little different. Instead of talking about a specific type of meteorite, I’ve decided to round up some of the latest and most interesting meteorite news on the web right now. At this point the biggest news in the world of meteorites is the brand new Martian meteorite, Tissint. About 24 lbs of material were recovered in Morocco last July and it represents one of the largest Martian meteorite finds to date.

News about the brand spanking new Martian meteorite:

Other interesting meteorite news

Meteorite Monday: The Holiday Edition

At last nights Skeptics in the Pub a very good friend of mine, Karla, gave me an unexpected gift: a small piece of a pallasite. These meteorites are what I like to call space rock bling and I actually wrote a post about them with the same title. Pallasites are a stony-iron meteorite that have a nickel iron body (or matrix) and are studded with olivine crystals. These meteorites are thought to represent the core/mantle boundary of a differentiated planetesimal that was impacted by another object and broke apart. The iron-nickel matrix is from the core and the olivine crystals are from the mantle. The pieces became incorporated during the impact much in the same way that you work chocolate chips into dough.

This is a piece of the Esquel pallasite from Argentina. It's considered one of the most beautiful due to its large olivine crystals. (Image from Wikipedia)

Mine is labeled as the Bela Pallasite, Russia, but I don’t have much information beyond that. Pallasites discovered in Russia include the Omolon, Pallosovka, and the Krasnojarsk. There was also one found Belarus called the Brahin. I’m not sure which of those mine could be from, but it’s one of the nicest gifts I’ve received in a long time. So, with that I want to say a big thank you to Karla! She made my evening with this piece of cosmic debris and also gave me the inspiration for today’s Meteorite Monday.

My own piece of pallasite! The 2nd piece in the middle has a somewhat visible olivine crystal in it. Bike key for scale.

Meteorite Monday: The Geminid’s and a quick update

My apologies for not having an actual post in a week. Last weeks physics midterm prevented me from doing my usual Meteorite Monday post and this weeks linear algebra midterm is looking to do about the same. I really dislike not being able to update my blog at least once a week, but sometimes, time isn’t on my side. Such is the life of the science undergrad! For that reason, this weeks post is going to be a quick one. I found a gorgeous video on Vimeo that showcases the Geminid meteor shower and I wanted to share it with everyone. Enjoy!

Fleeting Light: The High Desert and the Geminid Meteor Shower from Henry Jun Wah Lee on Vimeo.

Meteorite Monday: Using meteorites to find the origins of life

Whenever I’ve talked about meteorites, I’ve always approached them from the perspective of a petrologist. I like to look at them from the angle of mineral composition, weathering grades and shock effects. This approach reveals a lot about the early history of our solar system. However, there are other scientists who look at meteorites, not as planetary building blocks, but as possibly carrying the building blocks of life.

To me this is a pretty neat concept. The idea of meteorites being the building blocks of the planets and possibly the progenitors of life on our planet makes them all that much more fun to study. Last week I had the chance to hear most of a talk that was given by a Portland State alumni, Aaron Burton, about his work on meteorites in connection to the origins of life on earth. Unfortunately, I couldn’t stay for all the interesting chemistry because I had physics lab, but here’s a link to his blog where he talks about some of his research. He works at NASA-Goddard and part of his work involves making a meteorite “tea” out of a pulverized meteorite sample in order to identify the amino acids. Thankfully it’s for science, otherwise the idea of powdering a meteorite would reduce me to tears!

I wish I understood the chemistry of amino acids well enough to talk about it. However, I don’t so I’m going to post a video from NASA-Goddard that talks about this same subject.

Meteorite Monday: Impactites

A tektite and shatter cone from the Cascadia Meteorite Lab display case

My inspiration for this post came while I was working on the meteorite case for the lab. Initially we were going to put a relatively cheap meteorite in the display, but then we decided that wasn’t such a good idea. So, the next best idea was the throw in a few impactites. These are rocks that had the rather unfortunate (or fortunate depending on how you wanna look at it) luck to be in the zone of a rather large meteor impact. The extreme heat and pressure from these events really plays hell on the surrounding rocks.

An Australite tektite from the Australasian strewnfield (image from Wikipedia)

Impactites come in two flavors: tektites and shatter cones. Tektites are rocks that instantly melted and were flung into the air from the meteor impact. While airborne, the molten rock quickly cooled and took on an aerodynamic shape. Such shapes include tear drops, dumbells or even that of an inverted button found among Australites. Tektites are found only at four impact craters across the planet. As such, they can almost be as expensive as the meteorites themselves. The origin of tektites has been hotly debated in the past. In the 1950′s and 1960′s, researchers suggested that tektites were actually of lunar origin. However, tektites lack certain noble gases that are common to lunar meteorites (1).

Shatter cones are formed in the bedrock underneath the impact zone. They form at a relatively low pressure of less than 2 gigapascals (GPa). To put that into perspective, 2 gigapascal translates into approximately 290,000 psi. A shatter cone outcrops is a good sign that one is standing in an impact crater (2).

Shatter cone from the Wells Creek in Tennessee (Image from Wikipedia)

 

Sources:

1. Schneider, D.M., Tektites. The Meteoritical Society. Accessed on 10/17/2011

2. French, B.M. 1998. Traces of Catastrophe. Lunar and Planetary Institute. Retrieved on 10/17/2011

Meteorite Monday: Will return next week….

Because I am really behind on school work and I am also in charge of taking the glass display case for the meteorite lab and turning it from this…

It's kinda barren right now, but wait till I get done with it.

into something with actual rocks and a poster. No, we’re not filling it with meteorites, but with meteor”wrongs”. These are samples people suspected of being meteorites, but were either slag or terrestrial basalt. The part that’s taking the most time is the poster. I’m quickly becoming familiar with all sorts of Adobe programs. I’m doing all this in preparation for the annual fund-raising auction that Cascadia Meteorite Lab holds every year. So, on that note I’m going to get my head back into the books and try to get the display case looking glorious. I’ll be sure to post pics when I’m done with it.

Meteorite Monday: So you think you’ve found a meteorite

Last summer, when I did my first project with the meteorite lab, a gentleman had dropped of a box full of rocks. In this box were about four large ziploc bags, each loaded with rocks that were cataloged on 3×9 index cards. On these cards he noted where the samples came from, when they were collected, and most importantly, his assumption of what type of meteorite he found.  He obviously went to a lot of effort to collect these rocks and he was wanting us to tell him if any were meteorites.

Unfortunately, the gentleman didn’t find a single meteorite. Instead he had some really nice river rocks. They all displayed the smooth contours that typify rocks of a fluvial environment. To be fair, finding meteorites isn’t easy regardless of what it may look like on T.V. He was obviously passionate about his hunt as displayed by the number of locations he had visited during his meteorite search. So, in no way am I denigrating those that hunt the space rock that I may end up studying. It actually makes for a great teaching moment.

There are a few characteristics to look for when determining if you’ve found a meteorite. With two exceptions, most of the differentiating criteria for meteorite identification are not set in stone (sorry… I couldn’t resist the pun). There is some leeway because meteorites are from the same material which the earth formed. These guidelines are only valid for stony meteorites. Iron meteorites are obvious, so I won’t delve into those. So, let’s get into the first two definitive characteristics:

  1. Fusion crust- This is the shiny black surface that forms on a meteor as it rockets through the earths atmosphere. The exterior starts to melt from the friction generated heat, and if the meteor is large enough to survive its bumpy ride, instantly cools to form a glassy, black surface. It’s also common to see a matte surface instead of a glossy one. If you see a rock with this characteristic you’ve got a meteorite. One caveat though: not all meteorites will retain their fusion crust. It can weather away if left to the mercy of earth’s climate for too long. Just know that terrestrial rocks will not have a fusion crust.
  2. Chondrules- I would say that these are the definitive characteristic of a meteorite. No earth rock comes close to mimicking the appearance of these little spherical inclusions. They’re not always visible in a hand sample, but if you see them with  hand lens, you have a meteorite. The same caveat applies with these as well: weathering can sneak in through surface cracks and eat away at chondrules and leave behind the vague outline of relict chondrules.

    A meteorite displaying chondrules on the front facing cut surface and a glossy fusion crust on the non-cut surface (Image from Wikipedia)

  3. Regmaglypts- This fun-to-say word simply refers to the thumb-like imprints that form on the exterior of a meteorite. These are common in iron meteorites as well as stony meteorites. Unfortunately the process behind their formation isn’t one that I understand well enough to explain, so I’m not going to get into details.

    An iron meteorite showing large thumb prints, or regmaglypts, on its surface (Image from Wikipedia)

Now, let’s talk about the not-so-exclusive qualities of a stony meteorite

  1. Magnetism- This is shared by both space and earth rocks alike, making it a tricky diagnostic tool. The more iron-nickel you have in a rock, the more attracted it is to a magnet. However, meteorites that come from the moon and Mars are not magnetic. These are nearly indistinguishable from earth basalt unless you plan on doing an oxygen isotope analysis. For a great explanation on meteorites and magnetism, along with the best advice I’ve seen concerning the subject, click here.
  2. Rusting- This isn’t one I thought about including until I came across a YouTube   video where a guy said that the presence of rust spots was a sure fire sign of a meteorite. If this were the case, than the entire Columbia River Gorge is full of         meteoritic material and not basalt (if only it were true). I have seen plenty of basalt with oxidation that occurs in the form of rust.

I think that about covers the basics behind identifying meteorite hand samples. This list is by no means comprehensive so please don’t look to it as the only source of information available. The Cascadia Meteorite Laboratory, Northern Arizona University Meteorite Laboratory, and Washington University in St. Louis have great websites with even nicer pictures detailing how to identify a meteorite.

Meteorite Monday: The Hayabusa mission to Itokawa

Last week I wrote briefly about the Japanese Hayabusa mission to the asteroid Itokawa. This mission was pretty cool because we went to this piece of space rock instead of waiting a piece of it to come to us. In spite of the mechanical failures that nearly scuttled the mission, the Hayabusa probe was able to collect dust from Itokawa and bring it home for us to study.

I wanted to write a bit about this mission because meteorites come from asteroids. This is the equivalent of studying not only pumice from Mt. Hood, but the origin of the volcano as a whole and its relation to the Cascades. The collected dust particles tell us the story of how Itokawa formed and the types of meteorites that could come from it. From this evidence we can also gain more insight into the formation of the solar system.

The dust particles tell us that Itokawa is not a single chunk of space rock. It’s actually a patchwork collection of various asteroids that were broken apart and coalesced into a single piece of rock (1). In geology parlance we call this a breccia- or a big pile of rubble that cemented together over time. Sometimes this breccia is made up of the same rock type, other times it’s not.

This mega breccia of Titus Canyon can be seen as a terrestrial analog to the composition of Itokawa (Image from the National Scenic Byways Program)

In the case of Itokawa, we learned that it’s composed of asteroids with different thermal characteristics. Some of the breccia pieces have seen little heating and contain glass and clinopyroxene- a mineral common to type 3 and 4 meteorites. Others contain minerals such as diopside and large plagioclase crystals- these are indicators of the type 5 and 6 meteorites that have seen a higher degree of heating. (Nakamura et al., 2011)

From this information Nakamura et al.,  were able to construct a history for Itokawa. They suggest that Itokawa was large enough to undergo a high degree of thermal metamorphism, but was subsequently broken apart by collisions with other asteroids. These pieces fused together into the much smaller Itokawa that is present today. They also confirm that Itokawa is a member of the S-type asteroid family and that a direct link exists between it and ordinary chondrites.

A close-up of the surface of Itokawa. (Image courtesy of JAXA)

Muses Sea is the region from which Hayabusa took its samples. (Image from JAXA)

1. Nakamura, Tomoki, et al., Itokawa Dust Particles: A Direct Link Between S-Type Asteroids and Ordinary Chondrites. Science 333, 1113 (2011). DOI: 10.1126/science.1207758

2. For more close-ups of Itokawa, check out the image archive from JAXA.

Meteorite Monday: Asteroid Itokawa and the Hayabusa probe

Last week Science magazine published six articles about the results of the Japanese Aerospace Exploration Agency’s (JAXA) mission to asteroid Itokawa. In 2003 they sent a probe, Hayabusa, to gather information about Itokawa and collect soil samples.The poor space probe was plagued by malfunctioning engines, a rogue solar flare that fried computer systems and a mini-probe that failed to operate as it was designed. To JAXA’s credit, they still managed to collect dust from the surface of Itokawa and bring those particles back to earth for us to study.

Thanks to an acquaintance, Michael Barton, I was able to get my hands on one of the reports and I’ve been going through it with the hopes of sharing those results with my readers. Unfortunately, life has been rather hectic lately and I haven’t had the chance to properly read the paper and digest all the information in it.This may seem like a strange story for my Meteorite Monday column, but it makes sense when one considers that meteorites are just chunks of asteroids.

So, my goal for next week is to talk about some of the cool findings of this mission. Until then, you can click on the image to visit JAXA’s site and learn more about the Hayabusa and it’s mission to Itokawa.

Asteroid Itokawa (Image courtesy of JAXA)