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Meteorites

4 Posts tagged with the rocks tag
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Some meteorites, called CI chondrites, contain quite a lot of water; more than 15% of their total weight. Scientists have suggested that impacts by meteorites like these could have delivered water to the early Earth. The water in CI chondrites is locked up in minerals produced by aqueous alteration processes on the meteorite’s parent asteroid, billions of years ago. It has been very hard to study these minerals due to their small size, but new work carried out by the Meteorite Group at the Natural History Museum has been able to quantify the abundance of these minerals.

 

The minerals produced by aqueous alteration (including phyllosilicates, carbonates, sulphides and oxides) are typically less than one micron in size (the width of a human hair is around 100 microns!). They are very important, despite their small size, because they are major carriers of water in meteorites. We need to know how much of a meteorite is made of these minerals in order to fully understand fundamental things such as the physical and chemical conditions of aqueous alteration, and what the original starting mineralogy of asteroids was like.

 

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A CI chondrite being analysed by XRD. For analysis a small chip of a meteorite is powdered before being packed into a sample holder. In the image, the meteorite sample is the slightly grey region within the black sample holder. The X-rays come in from the tube at the right hand side.

 

The grains in CI chondrites are too small to examine using an optical or electron microscope so we used a technique known as X-ray diffraction (XRD). XRD is a great tool for identifying minerals and determining their abundance in a meteorite sample. We found that the CI chondrites Alais, Orgueil and Ivuna each contain more than 80% phyllosilicates, suggesting that nearly all of the original material in the rock had been transformed by water.

 

As part of the study we also analysed some unusual CI-like chondrites (Y-82162 and Y-980115) that were found in Antarctica. These meteorites have similar characteristics to the CI chondrites we studied, but also experienced a period of thermal metamorphism (heating) after the aqueous alteration. We found that the phyllosilicates had lost most of their water and had even started to recrystallize back into olivine, a process that requires temperatures above 500°C! The CI-like chondrites are probably from the surface of an asteroid that was heated by a combination of impacts with other asteroids, and radiation from the Sun; however, whether the CI and CI-like chondrites come from the same parent body, remains an open question.

 

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XRD patterns from the CI chondrites Alais, Orgueil and Ivuna. X-rays diffracted from atoms in the minerals are recorded as diffraction peaks. Different minerals produce characteristic diffraction patterns allowing us to identify what phases are in the meteorites. In this work we also used the intensity of the diffraction peaks to determine how much of each mineral is present.

 

This research has been published in the journal Geochimica et Cosmochimica Acta and can be accessed here.

 

King AJ, Schofield PF, Howard KT, Russell SS (2015) Modal mineralogy of CI and CI-like chondrites by X-ray diffraction, Geochimica et Cosmochimica Acta, 165:148-160.

 

It was funded by the Science and Technology Facilities Council (STFC) and NASA.

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As well as keeping you informed about our research we're going to use this blog to let you know more about our meteorite collection, especially the ones that aren't currently out on display.

 

All of us in the meteorite group are off to Casablanca, Morocco in September to present our research at the Annual Meeting of the Meteoritical Society (... more on that nearer the time). At the meeting there is going to be a special session about a very important meteorite called Orgueil.

 

It is 150 years since Orgueil was seen to fall in southern France (n.b. all meteorites are named after the place where they fell or were found so this one was seen to land near its namesake). We have several pieces of Orgueil, kept in the meteorite curation facility at the Museum.

 

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Me in the meteorite curation area. Most of our meteorites are kept in drawers like this.

 

Orgueil is important because it is part of a rare group of meteorites called CI chondrites. There are only five known CI chondrite 'falls' and Orgueil is by far the biggest, weighing 14 kg. We only have a total of about 7 kg of the other four CI chondrites so they are all very precious.

 

[A quick diversion into terminology - when meteorites are seen to fall and land we call them 'falls'. If a meteorite is found but no one saw it fall then it is called a 'find'. Falls are more valuable to scientists because they can be recovered more quickly and so are less likely to experience contamination or chemical alteration during their time on Earth.]

 

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A piece of Orgueil from our collection. All our meteorites have a unique number so that they can be identified.

 

When scientists analysed the chemistry of the CI chondrites they found that they are almost identical to the composition of the Sun. We think the chemistry of the Sun has stayed pretty much the same since it formed over 4.5 billion years ago and that the Sun contains over 99% of the mass in the Solar System.

 

This means that the Sun is very representative of the material that was present in the early Solar System; however it is very difficult to sample for what are probably obvious reasons. The compositions of other planets and many asteroids have been changed over time by chemical and physical processes so they are no longer representative of the early Solar System. As the CI chondrites are chemically very similar to the Sun we can study them to learn more about what the material in the Solar System was like when it formed 4.5 billion years ago.

 

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Different analytical techniques require different sample preparation. Here we have Orgueil "three ways": a disk (left) for infra-red analyses, powder (back-right) for x-ray diffraction analyses and chips (front-right) that can be polished for scanning electron microscopy.

 

Another of the CI chondrites, Alais, also fell in France about 50 years before Orgueil. Alais was found in 1806, just three years after one of the first scientific reports of a meteorite fall.

 

The report was written by Biot, a member of the French Academy of Science, and convinced the scientific community that meteorites were extra-terrestrial (apparently it was a much more exciting read than an earlier report by the German physicist, Ernst Chladni). Before this time meteorites were thought to be terrestrial rocks that had been struck by lightning, or rocks ejected from volcanoes. If Biot's work had not been published it is likely Alais would have been thrown away because it was initially thought to be fossilised peat.

 

The other three CI chondrite falls fell in the 20th century and are called Tonk, Ivuna and Revelstoke. The biggest piece of Ivuna is kept in our collection. It has been stored in a nitrogen atmosphere for the past twenty to thirty years. This protects it from the Earth's environment.

 

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We have the largest piece of Ivuna in a public collection anywhere. It is kept in a nitrogen environment to protect it from the Earth's atmosphere.

 

CI chondrites like Orgueil and Ivuna are also important as they contain organic material. This consists of molecules of carbon and hydrogen with some oxygen, nitrogen and sulphur. All this carbon makes the CI chondrites very black in colour - and perhaps easily mistaken for fossilised peat. They also contain a lot of water (up to 20%). One of our post-doctoral researchers, Ashley, is studying the mineralogy of Orgueil and other meteorites like it to find out more about water in the Solar System.

 

That the CI chondrites contain organic material and water is interesting because you need both these things in order for life to survive, and some people think that the building blocks for life on Earth could have been delivered by meteorites or comets. But - and it's a big but - you do not need life in order to have organic material and water, so they in themselves are not evidence of life coming from outer space.

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Hi all! Natasha here again, raring to tell you all about a most excellent trip that I’ve recently returned from. It was my first experience of the US and boy was it a good ‘un. Killing two birds with one Texan stone, I first went on a short course on geological applications for computed tomography (CT) in Austin, and then on to Houston for a visit to the NASA Johnson Space Center.

 

Micro-CT is a remarkable (and pretty novel) technique that uses X-rays to image specimens in three-dimensions, giving us a non-destructive way to see what’s inside. I use it to look at extraterrestrial material, but the scanner at the Museum gets used for all sorts! Sometime I'll do a more detailed post that goes into the physics of it all, but for now, back to the Lone Star State.

 

So my experience can be summed up in three words – humid, delicious and rocky! Everything is bigger in Texas. The cars (read pick-up trucks), the cakes, the personalities! Arriving into 40°C heat in Austin, my glasses immediately steamed up. After a short shuttle bus to the hotel, I was excited to meet my roommate for the duration of the course, a lovely PhD student studying drill cores with CT at the University of Florida.

 

Course on CT scanning

 

The short course was run by the High Resolution X-Ray CT Facility at the Jackson School of Geosciences (UTCT) in the University of Texas at Austin. This fantastic lab has been doing pioneering work in the geological applications of CT for almost 20 years. As well as getting a very helpful tutorial on their in-house software and talks on successful projects they have done, we also had the opportunity for a tour around the labs. UTCT has two CT scanners, which are optimised for different sizes and types of sample, including one instrument with detectors on microscope objectives. This means they can sort of ‘zoom in’ to features inside the specimen and get very high resolution images! Luckily they also have air conditioning in the lab otherwise I’m sure I’d have passed out from the heat!

 

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Ryan in the computer lab, learning how to use Blob3D.

 

That evening, all the course delegates were invited to a marvellous barbeque at the course director’s house, with home-smoked brisket, and my first Texan ribs! As well as enjoying dinner, I was dinner for certain unwelcome party guests… I left that night with about forty mosquito bites! 

 

Tuesday and Wednesday were likewise spent in workshops and tutorials on both CT hardware and software. One of the most important and useful aspects of attending the course was the chance to spend time with other rock-minded people, to share ideas on how to tackle problems or artefacts in the data, and to make contacts for future collaboration or discussion. We also managed to sneak in a couple of World Cup games along with a quick craft beer tasting walk through the city!

 

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Congress Bridge in Austin and the crowds awaiting the awakening of the million or so bats that live underneath.

 

Oh, and to continue the gastronomic theme, I tried a chimichanga, Detroit-style pizza, possibly the best pulled pork sandwich I’ve ever had, and breakfast burritos. Mostly yum!   

 

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This is a chimichanga, a deep fried burrito, soaked in cheese. Can’t say this one went down well!

 

As if often the case when you’re having fun, the days passed quickly, and it was soon time to leave Austin. I headed on to Houston for the next stage of the trip.

 

A trip to NASA

 

The Johnson Space Center is NASA’s base for human spaceflight training and flight control, and houses their Astromaterials Research and Exploration Science department. This means that all the astronauts are based there, and all the Apollo samples, Antarctic meteorites and samples collected during the Stardust and Genesis missions are kept there! It is possibly the most awesome facility that I could ever imagine.

 

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The Space Shuttle Endeavour flying over the Johnson Space Center on a Boeing 747 carrier aircraft. Copyright NASA.

 

The key reason I went to NASA was to visit Ryan Zeigler, the Apollo Sample Curator. Ryan is responsible for looking after all the rocks, soils and cores brought back by the Apollo astronauts on the six missions that landed on the Moon. Back in February, he brought four of these samples, from Apollo 14, 15 and 16, to the Museum, and we CT scanned them here together in the Imaging and Analysis Centre.

 

We haven’t written up the results yet, but all four scans were very interesting, showing different textures and inclusions. One of the most exciting finds was that of a very large clast of basalt in an Apollo 16 breccia (a rock made up of fragments of other rocks or minerals). Below is a visualisation I made of the CT data, which shows the outline of the sample and where the clast is located inside (the green mass). This kind of image is invaluable for curators who would like to know exactly where to slice into the rock to expose features of interest for science. The sample is about ten centimetres across.

 

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A visualisation of the location of a basalt clast within an Apollo 16 breccia, made using the Drishti program.

 

Blimey, that’s a long post already and I’ve barely got on to the coolest stuff that I saw and the rocks that I got to hold! I’ll leave it there for now but check back soon, as I’ll be doing another post all about the Lunar and Meteorite Laboratories! Here’s a taster:

 

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A lunar basalt, collected by Apollo 11. The only rock to have been brought from the Moon then taken back into space for a trip on the International Space Station.

 

Lastly, if you’re ever in Texas, check out the ribs at Rudy’s!

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Hello! I’m Jenny, a research scientist studying meteorites at the Natural History Museum. My work focuses on the timing of heating events in the early solar system, but more on that another time…

 

I’m part of a group of researchers, curators and PhD students who study meteorites and other extraterrestrial materials in the Museum’s Earth Sciences department. We study these rocks – using various laboratory techniques – so that we can better understand the formation of the solar system.

 

The Museum is a great place to carry out this research as its meteorite collection is one of the finest in the world; containing almost 5,000 pieces of 2,000 individual meteorites. Most of these come from asteroids, but we also have meteorites from the Moon and Mars. Our collection also includes objects formed during meteorites impacts.

 

We’ve decided to start this blog so that we can communicate our research to you and provide a more in depth look at the Museum’s meteorite collection. As it’s our first post I’ll give a few examples of why our research matters and how it gives important insights into the world and space around us.

 

  • The solar system formed about four and a half billion years ago. We know this from studying meteorites like this one, called Allende. It contains a component that is rich in calcium and aluminium (called calcium-aluminium inclusions or CAIs). These CAIs are the oldest solar system materials.

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This is a stone from the Allende meteorite. The white part is a calcium aluminium inclusion (we call them CAIs). These CAIs are thought to be the first solid material to form in the solar system.

 

  • There has not been a sample return mission to Mars yet so, for now, the only pieces of Mars available for scientific study on Earth are meteorites. These meteorites help us understand the volcanic processes that occurred on another planet. We are lucky enough to have a large (1.1 kg) piece of a martian meteorite called Tissint on display in the Vault gallery.

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The largest piece of the martian meteorite, Tissint. We keep it in a container called a dessicator to protect it from Earth's environment.


  • Meteorites contain a lot of water! You might think that asteroids are very dry objects, but in some meteorites up to 20% of their weight is made up of water. These meteorites are called carbonaceous chondrites as they contain organic carbon – this also makes them look very black in colour, as you can see in the photo of the Ivuna meteorite, below. Their chemical composition is very similar to the Sun, which means they preserve the most primitive solar system materials, unchanged for over four and a half billion years.

 

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This is a piece of the Ivuna meteorite. It looks very dark, almost black, because it contains a lot of carbon.


I hope you found that information interesting! I, along with the rest of the meteorite group, will use this blog to tell you more about our collection. We will also write about our individual research (what we hope to achieve, what lab techniques we use, conferences we attend), the curation of meteorites and our outreach activities. Check back soon for more!