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Sunday 24 May 2015

Q& A with an interstellar dust hunter

The following was a Q and A that was done several years ago - just before I was due to put it up I suffered a personal loss, and the post was forgotten about. Since it was a general Q and A on well established things about what this team does it is 99% still up to date, so without further ado:
Q and A with an interstellar dust hunter:
Manchester - my former stomping ground - is famous for a lot of things - Shameless (Although technically that’s Salford), the Hacienda (although that’s a block of flats now), Manchester United, people attempting to destroy the city centre, etc. But one of the things it should be famous for, is space science.

Above: If you think Astronomers don't know how to party....
No, aliens don't land there (not that people would mind) and it doesn't have a spaceport. But it does have Jodrell Bank, which is still one of the biggest radio ears on the sky Earth has, and the city has the Manchester University Isotope  Cosmochemistry and Geochemistry research group. Have a look at their blog, it's a brilliant window into the kind of space science that gets done right here on Earth.

Image above: The Manchester University team, with the Interstellar Dust Laser Explorer (IDLE) A combinastion of laser and mass spectrometre which can studying the chemical composition of the very tiniest fragments of matter from space. Image courtesy of Manchester University.
 The folks at Isotope Geochemistry and Cosmochemistry use a technique called 'isotope fractionation ', to help them understand the stories behind naturally occuring materials from space. The broad idea is this: Many elements come in a form with a different number of neutrons called its isotopes . This gives the isotope a different mass, so chemical reactions will use different isotopes up at different rates. By measuring the relative abundances of various isotopes - and the abundances of an isotopes decay products - the chemical story of a sample from space can be unravelled. 
Being a meteorite science fan, I thought I’d apply the power of sending an e-mail asking a few questions. Dr Henner Busseman, from the department, has given me more than a few answers!.
So, without further ado:
John: Firstly, thanks for taking the time to talk to me like this. Your group studies the chemical make up of materials from space, dating from 4.5 billion years ago. Could you tell us what kinds of samples you use, and how they are collected?
Dr Busseman: Meteorites – usually from museums and collections (either observed “falls” or “finds”), which are either from Antarctica or hot deserts. Interplanetary Dust particles (IDPs) which are collected in the stratosphere at 20km height by NASA aircraft or [are found] in Antarctic Ice. Solar wind particles collected with the GENESIS mission, and cometary Dust collected by the STARDUST mission.

John: Do samples of space dust tend to differ from meteorite falls?
Dr Busseman: Yes, IDPs tend to be more fragile, fine-grained, organic matter and C-rich, may overlap with most primitive meteorites

John: What do any variations tell us about the origins of these samples?
Dr Busseman: Most primitive samples ( which contain large isotope anomalies in elements like H, C, N, implanted noble gases, fluffy fine-grained texture) may originate from comets, more solid smooth samples with “hydrated” (OH-containing) minerals may originate from asteroids, other samples might be of terrestrial origin (spacecraft paint, exhaust, volcanic ashes)
John: I’ve often read that signs of thermal and aqueous alteration are due to a much greater amount of radiogenic heating in early solar system bodies. How small a body could have had a molten interior back then?
Dr Busseman: We're not sure. Maybe down to a few hundred km or less (perhaps 50?). Model-dependent.

John: How closely does the development of these tiny bodies compare to that of a terrestrial planet? Are some of the same geological proceses (Eg differentiation into core-mantle-crust) involved?

Dr Busseman: They follow the same processes. Terrestrial planets contain many protoplanetary bodies. You can have magma oceans and separation into core and mantle (and crust on top of it) also on asteroids.
John: Presumably any liquid water was confined to the subsurface. Does the presence of aqueous alteration imply large amounts of liquid water, or was it a rare occurrence confined to tiny spaces within rocks?
Dr Busseman: It could be both. You can have aqueous alteration on micrometer sized “contact layers” or due to local heat sources, and macroscopic presence of water, e.g. on the CI chondrite parent body

John: I’ve read that you use isotope fractionation - the relative abundances of isotopes of an element - to trace the chemical processes that have been at work in a sample. Could you give us an example of how measuring isotope fractionation tells us about the processes a sample has been through?
Dr Busseman: Large anomalies, enrichments of Nitrogen-15 relative to Nitrogen-14 or Deuterium relative to Hydrogen can occur only in the low density interstellar medium (ISM) at very low temperatures (e.g. around 10-30degrees Kelvin or so). Finding these anomalies in organic matter in IDPs and meteorites indicates that this matter formed in the cold regions of the protoplanetary disk or the ISM. Many other isotope signatures e.g. in Xe, C, N or O in various minerals are attributed to the production in the various layers in certain stars (e.g. supernovae)

John: How many geological processes can isotope fractionation be applied to learning about?
Dr Busseman: Many. Core formation/differentiation, formation chronology, activity of water, mineral formation/zoning, environmental temperatures during formation, volcanic processing etc etc. => there are many textbooks full of these mechanisms

John: Nickel iron meteorites are believed to be cores of ancient protoplanets/asteroids. How does looking at fragments of a place's core tell us about the history of the rest of that place?
Dr Busseman: The core contains one fraction of elements of the original starting material of an asteroid, the rest of asteroidal mantle/crust can be deduced.

John: Meteorites are often called ‘building blocks of the terrestrial planets’. Does the composition of modern meteorite falls match the overall composition of Earth?
Dr Busseman: No. “THE” building block material of the Earth has not been found yet.

John: Do meteorite falls contain the kinds of volatiles that make up our environment?
Dr Busseman: No. The origin of water and the present atmosphere (e.g. noble gases) is uncertain, and certainly requires many sources(incl. comets). The isotopic signatures of the volatiles in the meteorites and the terr. atmosphere do not match.

John: Both carbon rich meteorites, and samples collected from comets, have shown chemicals that may have been involved in the abiogenesis of life on Earth - for example nucleobases and nucleobase analogues found last year in the Murchison meteorite. What do these tell us about the beginning of terrestrial life?
Dr Busseman: It could simply be possible that some of the ABIOTIC building blocks necessary for the evolution of life (e.g. as simple as CN functional groups or basic organic molecules) might have been delivered by meteorites/comets. If these were available also during the formation of other bodies (in our solar system, but also in other stellar systems) at least some of the basic ingredients necessary for extraterrestrial life might have been present elsewhere. However, suitable conditions are needed (temp., atmosphere, etc...)
John: Thank you for you time Dr Busemann.


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