New insights into the evolution of the solar system
Chondrules in a section of primitive chondrite, Image courtesy of M. Champenois CRPG.
The grains and solids that have accumulated in meteorites can provide important insights into the evolution of the solar system. Dr Marc Chaussidon explains how the CEMYSS project’s work in developing new analytical techniques will help researchers learn more about the early years of the solar system Studies of meteorite composition can offer valuable insights into the formation of the solar system. Meteorites formed in the early years of the solar system have accumulated grains and solids throughout their evolution; this area forms the primary research focus of the CEMYSS project. “The idea of our project is to study meteorites and develop new analytical techniques to measure the isotopic www.euresearcher.com
composition of different components of meteorites. This will help us put the evolution of the solar system into the context of what astrophysicists have observed in young stars and their accretion disks,” says Dr Marc Chaussidon, the project’s scientific coordinator. Researchers in the project are using a special analytical tool called an ion microprobe to analyse the isotopic composition of meteorites. “We
can look at how the sun was formed from the mixture of inter-stellar gas and dust, and how this dust merged into small objects which then grew together to make bigger objects and planets,” explains Dr Chaussidon. “One very important observation which has emerged from various studies is that the processes involved in forming the sun were very rapid and led to the rapid formation of the
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Thin section of the Chassigny metorite showing olivine crystals from the mantle of Mars. Image courtesy of B. Zanda MHNH. first small planets, called planetesimals, which were 60-100 kilometres in diameter.”
Planetesimal formation It is thought these planetesimals formed very rapidly around the sun in the accretion disk over the first 2-3 million years after its formation. Previously it was believed that planets grew through a gradual process of hierarchical evolution, but recent astrophysical models have shown that it was in fact possible to go straight from dust to planetesimals; this has significant implications for researchers understanding of meteorites’ chemical composition. “There are samples of small planetesimals in meteorites, and if we can identify the types of planetesimals they came from then we can date the sample and measure its composition. We are trying to find the logical steps in between these stages, to determine the timescale which operated in our own solar system, and to compare that
to astrophysical models,” outlines Dr Chaussidon. By measuring the abundance of short-lived radioactive nuclides in meteorites Dr Chaussidon says it is possible to investigate the ages of those meteorites very precisely. “We are measuring the products of radioactive elements which were present at the beginning of the solar system,” he explains.
Planetary evolution This was probably due to the heat generated by the decay of 26Al, showing that short-lived radioactive nuclides are not only effective tools for establishing the chronology of solar processes, but also help control the evolution of planets. The project’s work in developing an ion microprobe, a type of mass spectrometer,
The idea of our project is to study meteorites and develop new analytical techniques to measure the isotopic composition of meteorites. This will help us put the evolution of the solar system into the context of what we and astrophysicists have observed in young stars and their accretion disks The short half-life of these radioactive nuclides means researchers can use them to reconstruct the chronology of early processes in the solar system, even within the wider timescale of its evolution. The two key nuclides being used are aluminium-26 (26Al), which has a half-life of approximately 700,000 years, and b e r y l l i u m -10 (10Be), which Dr Chaussidon says was probably produced by the sun. “When the sun formed it was very
The instrument developed for the purposes of the CEMYSS project: ion microprobe Cameca 1280HR2.
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active and it emitted a lot of particles. The particles emitted by the present day sun make the solar wind radiation – the early sun was probably much more active than the present day sun,” he explains. These particles collided with the gas and dust of the accretion disk, leading to nuclear reactions and the production, among others, of 10Be, which is a signature of the activity of the young sun. “The sun was very active during the first 1-2 million years after its formation, so 10Be is the signature of this period. It can be used to relate components of meteorites to the activity of the young sun,” continues Dr Chaussidon. “Another reason for focusing on these short-lived radioactive nuclides is that nuclides like 26Al were probably responsible for the fact that some of the early planets heated very rapidly and melted.”
means these short-lived radioactive nuclides can be measured to a high level of precision. “Take 26Al, which decays to magnesium 26 (26Mg); if you measure the three magnesium isotopes you can precisely determine the excess amount of 26Mg, which is derived from the decay of 26Al. You can then calculate the age of the meteorite much more precisely,” explains Dr Chaussidon. The project works with astrophysicists to model the production of 26Al and its distribution in the disk, and hence better understand the processes which control it. “If you compare two samples containing excess amounts of 26Mg, then you can say for instance that the one which contains less is younger than the other, because the 26Al has decayed before its formation,” says Dr Chaussidon. “This is of course based on the questionable assumption that originally the 26Al distribution was
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homogenous in the disk.” This work on the distribution of 26Al is just part of the project’s approach. Other elements were produced continuously over a period of approximately 1-2 million years in the early years of the solar system; by also measuring the abundance of 10Be Dr Chaussidon says it is possible to gain further detail. “We can couple different short-lived radioactive nuclides which have different sources, different half-lives and which decay at different rates. By coupling them within the same meteoritic component we can put much better constraints on its age and the processes involved in its formation,” he stresses. This is also relevant to the project’s goal of discovering the very first planetesimals; oxygen isotopic composition is a very important tool in this regard. “Oxygen has three stable isotopes. We know that oxygen isotopic composition is very variable in the solar system,” explains Dr Chaussidon. “For instance you can identify a meteorite from Mars simply because of its oxygen isotopic composition. Presumably, planetesimals also had different oxygen isotopic compositions, reflecting the variable oxygen isotopic composition in the accretion disk.” The source of this variability has not been established. Different possibilities have been suggested, which in turn could be used to help identify planetesimals; alongside oxygen, Dr Chaussidon is also looking at nitrogen isotopic composition in the early solar system. “We are working to determine the oxygen and nitrogen isotopic composition of the sun itself,” he says. The project is also using data gathered by other initiatives in this work. “I have been working to measure the nitrogen isotopic composition of the sun
Primitive chondrite with its fusion crust. Image coourtesy of B. Zanda MHNH
by analysing samples from NASA’s GENESIS mission, which sampled the solar wind,” continues Dr Chaussidon. “Another group did the same with oxygen. This established that the sun is very different in oxygen and nitrogen isotopic composition from other objects in the solar system, including the earth and meteorites. Initially there was extremely wide variation in oxygen isotopic composition – we are trying to find components within meteorites that we think are fragments of those planetesimals that formed very early. We can then pair these fragments together by measuring their oxygen isotopic composition.” The project’s findings could then be integrated with those from other initiatives to gain a more complete picture. This will be enormously relevant to our understanding of how the solar system evolved. “Our results will be used to establish times and processes in the early solar system. So they are very important to understanding the growth of planets,” stresses Dr Chaussidon. The next step is to discover very short half-life radioactive nuclides which would be important in linking the formation of some components in the meteorites to the early evolution of the sun. “For instance irradiation processes around the sun could have shaped and modified the composition of the dust. This would be very important to understanding the chemical composition of planets,” says Dr Chaussidon. “Our efforts at the moment are focused on trying to discover these short-lived radioactive nuclides. We think we have also identified some of these very early planets which were destroyed, and we are working on trying to reconstruct their geological history based on much more precise measurements.”
At a glance Full Project Title Cosmochemical exploration of the first 2-3 millions years of the solar system (CEMYSS) Project Objectives Make progress in our understanding of the processes by which the nebular gas was transformed into solids and planets around the early sun at the very beginning of the solar system. Project Funding 12 million euros Contact Details Project Coordinator, Marc Chaussidon CRPG-CNRS BP 20 54501 Vandoeuvre-lès-Nancy France T: +33 3 83 59 42 25 E: chocho@crpg.cnrs-nancy.fr W: www.crpg.cnrs-nancy.fr/index.php W: www.crpg.cnrs-nancy.fr/Sonde/ intro-sonde.html
Marc Chaussidon
Project Coordinator
Marc Chaussidon graduated from the Ecole Nationale Supérieure INSU de Institut national des sciences de l'Univers Géologie in Nancy France and is Directeur de Recherches CNRS at the Centre de Recherches Pétrographiques and Géochimiques in Nancy. He is a geochemist/cosmochemist specialist of isotopic analysis by ion microprobe. His interests concern the study of formation and early evolution of the solar system and the Earth.
INSU
Institut national des sciences de l'Univers
CRPG www.euresearcher.com
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