© H. Raguet/CNRS Photothèque Details of meteorites can be studied with a polarizing microscope: Here, we can observe the structure of chondrules, the silicated spherules of millimetric dimensions that are found in certain meteorites known as chondrites.
© H. Raguet/CNRS Photothèque
Details of meteorites can be studied with a polarizing microscope: Here, we can observe the structure of chondrules, the silicated spherules of millimetric dimensions that are found in certain meteorites known as chondrites.
The eighteenth century architecture of the National Natural History Museum (MNHN) in
The Rich Trawl from Stardust
© CNRS IAS, Orsay - LSPES, Lille I The cometary grains that strike the collector at 6 km/s create craters on the aluminum, which resembles this image obtained in the laboratory.
© CNRS IAS, Orsay - LSPES, Lille I
The cometary grains that strike the collector at 6 km/s create craters on the aluminum, which resembles this image obtained in the laboratory.
This trawl of dust was collected and trapped in an extremely porous gel known as “aerogel,” when the space probe passed through the comet's tail. These mythical celestial bodies are in fact conglomerates of ice, dust, and rocks, which evaporate when they come close to the Sun and eject a diffuse atmosphere trail known as a “coma” or “tail.” The Stardust probe passed within 500 kilometers of the comet's nucleus, allowing it to sweep up the precious grains of dust which have since been shared with a few hand-picked laboratories (including seven with CNRS). Apart from the Nano-analysis Laboratory, which will perform isotopic mapping of ten or so grains, CNRS' Petrographic and Geochemical Research Center (CRPG)2 in the city of
But in addition to this precious “trawl,” the study of the “net” itself will also provide a wealth of information: At the Space Astrophysics Institute (IAS)3 in Orsay and at the Solid State Structure and Properties Laboratory (LSPES)4 in
© H. Raguet/CNRS Photothèque The isotopic composition of microscopic grains can be determined by mass spectrometry. The NanoSIMS microprobe performs this analysis over dimensions of 50 nanometers, the size of only a few molecules.
© H. Raguet/CNRS Photothèque
The isotopic composition of microscopic grains can be determined by mass spectrometry. The NanoSIMS microprobe performs this analysis over dimensions of 50 nanometers, the size of only a few molecules.
The Museum's Treasures
These extraterrestrial fragments are not the first ones to have found their way into the museum: Its collection of one thousand or so meteorites is one of the most impressive in the world. “Obviously, these rocks have been studied very closely, but NanoSIMS will reveal details that until now were unattainable.” For example, the famous Murchison meteorite, which fell in
Other jewels in the collection are chondrites, which Brigitte Zanda (assistant professor at the Museum) is studying in the laboratory. These small beads included in meteorites, rich in silicates, magnesium, and iron, are the first solid objects from the solar system. And, last but not least, there is another rare specimen in the collection: the Bencubbin meteorite. As Claude Perron, CNRS researcher, explains, “it was formed from materials that have been pulverized and then re-condensed. Studying it will make it possible to reconstitute several violent episodes that took place during the infancy of the solar system.”
The Earth's Past
While waiting for other missions (see box) to collect cosmic grains, some terrestrial rocks could unveil an important slice of the history of the solar system: the Earth's past, its climates, and the circumstances that presided over the appearance of life. For instance, the study of organic matter contained within 3.5 billion-year-old fragments of flint has revealed one of the oldest traces of life. “With Sylvie Derenne of the ENSCP,9 we have identified a 'biosignature,' a long carbon chain from the alkane family, proof of the existence of life,” explains Robert. In fact, the cellular membrane is characterized by an enzymatic process that favors chains constituted of an uneven number of carbon atoms over those comprising an even number. This biosignature will be used while searching for life in terrestrial samples. The NanoSIMS could cast new light on these questions. It is now widely accepted and proven that the measurement of chemical elements and isotopes present in a minuscule grain can reveal much about the history of the cosmos. “Twenty years ago, when Marc Chaussido (CRPG) and I first thought of these methods, cosmochemistry was underrepresented in
> For further information:
1. Laboratoire d'étude des matériaux extraterrestres. Unité CNRS “Nano-analyses” (CNRS / MNHN joint lab).
2. Centre de recherches pétrographiques et géochimiques (CNRS lab).
3. Institut d'astrophysique spatiale (CNRS / Université Paris-XI joint lab).
4. Laboratoire de structures et propriétés de l'état solide (CNRS / Université Lille-I / ENSC Lille joint lab).
5. Centre de spectrométrie nucléaire et de spectrométrie de masse (CNRS / Université Paris-XI joint lab).
6. Aleon J. et al., “Extreme oxygen isotope ratios in the early Solar System,” Nature. 437 (7057): 385-8. 2005.
7. All meteorites were formed from the same source matter and at the same time as the Sun.
8. Spallation is the splitting of an atomic nucleus into nucleons and lighter nuclei when it is struck by a very high energy particle.
9. ENSCP: Ecole Normale Supérieure de Chimie de Paris.