Micrometeorites

Micrometeorites are extraterrestrial particles that survive their entry into the Earth’s atmosphere and that are collected at the Earth’s surface. They dominate the influx of extraterrestrial matter on Earth and they must be taken into account in order to quantify the diversity of the objects of the Solar System and the chemical budget of the extraterrestrial matter to the Earth.

Micrometeorites are collected from different environments, from deep-sea sediments to polar ice and to urban roofs. The collection I study comes from the Victoria Land Transantarctic Mountains, in Antarctica, where micrometeorites were collected on the top of nunataks (Rochette et al., 2008). This collection is hosted by the Museo Nazionale dell’Antartide at Siena, where I did a postdoc.

Figure 1. Images of micrometeorites, from Folco and Cordier (2015)

The Transantarctic Mountain collection includes thousands of micrometeorites that accumulated over the last million years.
Like in other collections, these micrometeorites show large ranges in shape, color, texture, mineralogy that are used to divided them into different groups (Genge et al., 2008):

  • The unmelted micrometeorites are angular particles which suffer from limited melting during their atmospheric entry and in which the different components of meteorites are easily identifiable (matrice, anhydrous silicate grains, chondrules, etc).
  • The melted micrometeorites or cosmic spherules are spherical particles which have been totally melted during atmospheric entry heating (with the formation of a melt droplet).
    The composition of the cosmic spherules varies between iron-rich (I-type) to silicate-rich (S-type). Amongst the S-type a wide range of texture is observed with barred-olivine spherules, porphyritic spherules, cryptocrystalline spherules and glassy spherules.
  • The scoriaceous micrometeorites are partially melted. They are highly vesicular but otherwise, their characteristics are intermediate between unmelted and totally melted micrometeorites.

Figure 2: Backscattered electron images of cosmic spherules from Folco and Cordier (2015). (a-c) Glass cosmic spherule, one with a Fe-Ni-S metal bleb (white). (d-j) Cryptocrystalline cosmic spherules. (j-l) Barred olivine cosmic spherules. (m) Porphyritic cosmic spherules. Dark grey Mg-rich olivine grains are relicts that did not totally melt during atmospheric entry and they are overgrown by more Fe-rich olivine microphenocrysts.

My main interest is to understand how the processes occurring during atmospheric entry modify the texture and composition of the particles and, in turn, what are the chemical/mineralogical features that can allow us to decipher the parent body of the particles and explore the diversity of the inner solar system dust complex.
This is a complex issue as a range of short-lived processes occur during atmospheric entry: heating and cooling, melt/grain reactions, evaporation, oxidation or reduction, immiscibility between metal or sulphide liquid and silicate liquid.
In addition, direct comparison between micrometeorites and meteorites is complicated as micrometeorites may not be representative of the parent body texture and composition due to their relative small size.

Publications

  • Baecker B., Ott U., Cordier C., Folco L., Trieloff M., van Ginneken M., Rochette P. (2018) Noble gases in micrometeorites from the Transantarctic Mountains. Geochimica et Cosmochimica Acta, 242, 266-297.
  • Cordier C., Baecker B., Ott U., Folco L., Trieloff M. (2018) A new type of oxidized and pre-irradiated micrometeorite. Geochimica et Cosmochimica Acta, 233, 135-158.
  • Folco L. and Cordier C. (2015) Micrometeorites. In Notes in Mineralogy: Planetary Mineralogy, ed. M. Lee, European Mineralogical Union, 15, pp. 253-297.
  • Cordier C. and Folco L. (2014) Oxygen isotopes in cosmic spherules and the composition of the near Earth interplanetary dust complex. Geochimica et Cosmochimica Acta, 146, 18-26.
  • van Ginneken M., Suavet C., Cordier C., Folco L., Rochette P., Sonzogni C. (2012) Oxygen isotope composition of meteoritic ablation debris from the Transantarctic Mountains: Constraining the parent body and implications for the impact scenario. Meteoritics and Planetary Science, 47, 1738-1747.
  • van Ginneken M., Folco L., Cordier C., Rochette P. (2012) Chondritic micrometeorites from the Transantarctic Mountains. Meteoritics and Planetary Science, 47, 228-247.
  • Cordier C., Suavet C., Folco L., Sonzogni C., Rochette P. (2012) HED-like cosmic spherules from the Transantarctic Mountains, Antarctica: Major and trace element abundances and oxygen isotopic compositions. Geochimica et Cosmochimica Acta, 77, 515-529.
  • Suavet C., Cordier C., Folco L., Rochette P., Gattacceca J., Sonzogni C., Damphoffer D. (2011) Non carbonaceaous chondrite-related large cosmic spherules from the Transantarctic Mountains. Geochimica et Cosmochimica Acta, 75, 6200-6210
  • Cordier C., Folco L., Suavet C., Rochette P., Sonzogni C. (2011) Major, trace element and oxygen isotope study of glass cosmic spherules of chondritic composition: the record of their source material and atmospheric entry heating. Geochimica et Cosmochimica Acta, 75, 5203-5218.
  • Cordier C., van Ginneken M., Folco L. (2011) Nickel abundance in stony cosmic spherules: constraining precursor material and formation mechanisms. Meteoritics and Planetary Science, 46, 1110-1132.
  • Cordier C., Folco L., Taylor S (2011) Vestoid cosmic spherules from the South Pole Water Well and Transantarctic Mountains (Antarctica): A major and trace element study. Geochimica et Cosmochimica Acta, 75, 1199-1215.