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Meteorites

3 Posts tagged with the chondrites tag
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Last December, Epi Vaccaro (one of our PhD students) and I went to two scientific meetings in Tokyo, Japan. Our aims were to present some of the research that we’ve been doing at the Museum and to meet other scientists who work on similar samples and topics.

 

First up was the Fifth Symposium on Polar Science at the National Institute of Polar Research (NIPR). Since the early 1960s, the NIPR has used Antarctic stations to carry out research into a wide range of areas including climate, atmospheric science and biology. Fortunately for us, they are also interested in meteorites and, after several 'meteorite hunting'expeditions in the Antarctic, now have one of the largest collections in the world.

 

I spoke at the meeting (despite a serious case of jetlag!) about differences I have observed between the mineralogy of CI chondrites that were seen to fall to Earth, such as Orgueil, and those that have been recovered from the Antarctic. These CI meteorites are important as they show very similar characteristics to the surfaces of some asteroids that are soon(ish!) to be visited by space missions.

 

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Presentations were temporarily suspended at the NIPR meeting as we watched the launch of the Hayabusa-2 mission.

 

One of these missions is the Japanese Aerospace Exploration Agency (JAXA) Hayabusa-2 spacecraft, which aims to collect material from a primitive asteroid and return it to Earth. We think that this material will allow us to learn more about water and life in the early solar system.

 

The samples won’t touch down on Earth until 2020 but the spacecraft was launched (after a few days delay) during our stay in Japan. I think that watching a tiny spacecraft being hurtled into space on the back of a rocket, whilst sitting alongside the people who have invested so much time and energy into the mission, was one of the most tense afternoons of my life!*

 

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Model of the Hayabusa spacecraft at the Japanese Aerospace Exploration Agency (JAXA).

 

You may have guessed from its name that Hayabusa-2 is actually a follow up to the original Hayabusa spacecraft, which (despite a few bumps along the way) in 2010 became the first ever mission to collect material from an asteroid and bring it back to Earth.

 

Hayabusa 2014 Symposium at JAXA. The meeting covered diverse subjects such as space weathering and sample curation, and also included a talk by Epi on the challenges of analysing very small samples using non-destructive techniques.

 

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Epi presenting his work at the Hayabusa 2014 Symposium at JAXA.

 

Sample return missions are challenging and expensive but produce very exciting science, as I witnessed at JAXA. There are limits on what kinds of scientific experiments can be carried out remotely, but returned samples from the asteroid belt will provide a wealth of new information about our solar system’s past.

 

*You’ll be pleased to hear that the launch was successful and Hayabusa-2 is safely on its way.

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A guest post by Helena Bates, undergraduate student at Imperial College London.


This summer I had the opportunity to work alongside scientists in the Mineral and Planetary Science Division at the Natural History Museum on a project sponsored by the Paneth Trust, a scheme which offers bursaries to undergraduates so that they can do a summer internship in fields relating to meteoritics.

 

The project I joined was led by Ashley King and involved investigating minerals that were created by aqueous alteration in CI and CM carbonaceous chondrites. These types of meteorites have had almost all of their original material altered by water into fine-grained clay type minerals, which are so small they cannot be easily studied by looking through a microscope. Instead, we used a process called X-ray diffraction to identify mineral components. When a small beam of X-rays is focused on the sample it produces a diffraction-pattern unique to the minerals present.

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Ashley and I are busy using the X-ray diffractometer.

 

Usually this process involves grinding up a sample of a meteorite, and any information about where in the meteorite a certain mineral is located is lost. However, the alteration that the meteorite experienced was probably not uniform so knowledge of the distribution of aqueous alteration minerals is important. If we can see where the alteration took place within the meteorite this can help us put constraints on the role of water in the early solar system and perhaps even see how the water moved through the sample! So rather than grinding up samples we carried out X-ray diffraction on thin sections of meteorites.

 

We looked at a total of 4 meteorites, all of which were found in Antarctica and on loan to us from NASA and JAXA. They were; Y-82162, a CI chondrite, LAP 02277 and MIL 07689, both of which were CM1 chondrites, and MCY 05231, a CM1/2.

 

HBimage1.jpgA thin section of meteorite LAP 02277 with dots showing where X-ray diffraction patterns were collected.


For each meteorite we produced maps of various minerals that are produced by reactions with water, including phyllosilicates, iron oxides and carbonates. These maps give us spatial information about where some minerals are located in relation to others. Obviously this is just the beginning of the technique, but it is easy to see how this can be taken further to produce larger maps which can show how water moved through the sample. This will help us understand the role of water during the formation of asteroids, 4.6 billion years ago.

 

Thank you so much to everyone at the Natural History Museum, especially Ashley King, who let me help with his research, and thank you to the Paneth Trust for helping fund this internship – it was an incredible experience!

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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.