Evidence of a Tunguska-like event over Antarctica ca. 481,000 years ago. My research focused on the discovery of spherulitic aggregates found within micrometeorite traps from Miller Butte, Victoria Land, Antarctica. The traps have been collecting extraterrestrial over the last million years. These spherulitic aggregates have been found together with thousands of micrometeorites, which are dust sized particles reaching Earth’s surface. The unique structure of the spherulitic aggregates makes them easy to differentiate from micrometeorites (see Fig. 1). This study aimed at determining the nature and mechanism of formation of this new kind of extraterrestrial material. Fig. 1: Scanning Electron Microscope Backscattered Electron image of a spherulitic aggregate. The study of the mineralogy of the spherules constituting aggregates, essentially made of olivine and magnesioferrite, allowed their identification as meteoritic ablation spheres (MAS), which are melt droplets that detached from the heated surface of a meteorite during its entry in Earth’s atmosphere. The bulk composition of the spherulitic aggregates is chondritic, suggesting that the impactor was a chondrite. Similar spherulitic aggregates and microscopic spherules were discovered in an extraterrestrial dust layer discovered in the EPICA-Dome C and Dome Fuji ice cores (see Fig.2). The dust layer has been dated in both cores and is ca. 481,000 years old and is therefore likely to derive from the same event. The strong mineral and textural affinities between these materials and their uniqueness suggest that they are paired, therefore documenting a continental scale meteoritic event that occurred over Antarctica ca. 481,000 years ago. A minimal size of the impactor of ca. 40m has been estimated from the minimal area of repartition of the MAS (Fig. 2). Numerical models of the atmospheric entry of meteorites suggest that a chondrite of this size will explode in the atmosphere before reaching Earth’s surface. Such events are called “airbursts”. A famous airburst event is the Tunguska impact, which occurred in Siberia in 1908. Numerical models also show that such an airburst could scatter MAS over a large area, which is consistent with what we observe in Antarctica.>/p> Fig. 2: Suggested minimal area over which the MAS were spread. This outstanding discovery of MAS gives new clues as to what happen during an airburst event. Airbursts on the scale of the Tunguska event are thought to occur every 500-1,000 years on Earth. This work may therefore give a way of spotting these events in the geological record. This work was published in April 2010 in Earth and Planetary Science Letters n°293. The discovery was disclosed on the BBC news website (http://news.bbc.co.uk/2/hi/8547534.stm). Currently, I am working on a set of eight giant unmelted micrometeorites (size >300 µm). The aim of this work is to constrain the nature of the extraterrestrial materials found in this unusual size fraction. The large size of the particles allows the use of a wide range of analytical methods and therefore allows a better classification of the micrometeorites on the basis of their petrology and mineralogy. This would allow a better understanding of the various materials constituting the micrometeorite population reaching Earth’s surface.