Meteoritic chondrules are the record of widespread melting in the early solar system, either in the protoplanetary disk or associated with the formation of planets. Mechanisms proposed for chondrule formation include melting of silicate dust aggregates by gas shock waves, melting during passage of dust through bow shocks around planetary embryos, and melting during collisions of planetesimals. The thermal histories of such events are being modelled and we can compare them to measured chondrule cooling rates as a criterion for the chondrule formation mechanism. Most estimated chondrule cooling rates are based on oxidized (Type II) chondrules, because their ferroan olivine crystals are strongly zoned, and the zonation in Fe/Mg and minor elements can be simulated in crystallization experiments and diffusion calculations. These cooling rates, even though somewhat controversial, are generally assumed to apply to all chondrules, and are one of the main reasons for the support of the gas shock heating mechanism. However, Type II chondrules are abundant only in ordinary chondrites, which are associated with S-type asteroids and therefore probably formed in the inner solar system. The cooling history of reduced (Type I) chondrules, dominant in carbonaceous chondrites (related to C-type asteroids and comets) and therefore formed widely throughout the protoplanetary disk is thus most important, yet very poorly constrained, because their forsteritic olivine is unzoned. We propose to apply two new methods to the determination of the cooling rates of Type I chondrules, taking advantage of several state-of-the-art techniques. We will study samples of the Paris CM chondrite and the Renazzo CR chondrite, both from the MNHN collection, together with the Isheyevo CH/CBb chondrite. Computer tomography (CT) scanning will be used to localize a number of Type I chondrules with metal grains on the surface. We will prepare serial polished sections to intersect features of interest, and characterize the chondrules by SDD-SEM, EMP, and EBSD. A representative number of chondrules containing Ca-rich pyroxenes and metal will be selected for further studies. Metal grains on the chondrule surfaces will be analyzed by LA-ICP-MS and the diffusion profiles of Cu and Ga will be used to determine cooling rates. From the same samples, we will prepare FIB sections of Ca-rich pyroxenes for TEM examination. The objective will be the study at the nanometer scale of diopside-pigeonite exsolutions that developed during cooling. The exsolution wavelength will be used to determine cooling rates. We will thus have two new and independent cooling rates for temperatures near 1200°C. Concordance of the rates would remove controversy about chondrule cooling history. The obtained cooling rates will be confronted to models, and thus allow to evaluate the heating mechanisms that prevailed throughout the disk in the early solar system.

The core of the FRIPON project (Fireball Recovery and Planetary Inter Observation Network) is to (i) determine the source regions of the various meteorite classes, (ii) collect both fresh and rare meteorite and (iii) perform scientific outreach. This will be achieved by building the densest camera network in Europe, based on state of the art technologies and associated with a participative network for meteorite recovery. The present project aims to covering the cost of setting up this network, which will be achieved over the next 3 years. However, our goal is to make it sustainable for at least 10 years. The only way for determining the source regions of meteorites is to witness the falls live to derive their orbits. We propose to install a network of 100 digital cameras covering the entire French territory. It will use the most recent technology: to get orbital elements with unprecedented accuracy, we will use radio receivers to measure the Doppler effect generated by the GRAVES radar echo on the meteor head. Accurate orbits of the bolides will allow us to (i) constrain their source region and (ii) compute impact locations with a ~1 km accuracy (giving us a real chance of recovering the meteorites). We need about one thousand orbits to start statistical work for meteorite source detection. This goal will be achieved within 3 years as there is on average one bolide per night over France. In addition, considering that there are 5 to 25 falls over France per year (~15 on average), during the 10 years life of the project, there will be ~150 falls out of which we realistically expect to recover ~30 fresh meteorites including 4 to 8 important ones (i.e. not ordinary chondrites), based on fall statistics. Regional centers (mostly scientific laboratories) will form the basis of our network as they will be responsible for ~4-5 video cameras and one radio receiver. Aside from these laboratories, cameras will be installed in all kinds of public structures. All cameras images will be made available to the public. After each ‘event’, the core team will decide, upon analysis of the fireball parameters, whether or not to organize a recovery campaign. Once our network is fully operational, we will cooperate with our colleagues in the adjoining countries by (i) providing them with data on relevant falls and (ii) exporting the expertise developed in France to expand the network. Finally, as our network will be designed to require a minimum of maintenance, we foresee operations for about 10 years with minimal additional costs with respect to the starting ones (mostly replacement of some of the cameras, search party funding being sought by the regional centers). Our project is original in several ways. (i) It is inter-disciplinary, involving experts in meteoritics, asteroidal science as well as fireball observation and dynamics. It will thus create new synergies between prominent institutions and/or laboratories, namely between MNHN, Paris Observatory and Université Paris Sud in the Parisian region; and between CEREGE and LAM in the Provence region. Overall, scientists from over 25 laboratories will be involved, representing a mix of scientific disciplines and covering all the regions of France. (ii) It will generate a large body of data, feeding databases of interest to several disciplines (e.g. bird migration, variations of the luminosity of the brightest stars, observation of space debris, meteorology…). (iii) It will for the first time involve the general public (including schools) in the search for the meteorite falls, thus boosting the interest for science. (iv) Our observing technique will be completely new as it will integrate complementary tools (state of the art digital cameras in the visible range, radio and meteorological data) in a network denser than any built before (there are now about 50 all-sky cameras in Northern/Eastern Europe and there will be 100 in France only).