Antarctic large micrometeorites: state-of-art and preliminary results

The Earth ‘s accretion rate of meteoric material in a single typical year is dominated by submillimeter particles with the peak of the micrometeoroid mass distribution occurring at particole size between 0.1and 1.0 mm, as evidenced by spacecraft meteoroid detectors and meteor radar techniques. Micrometeors and micrometeorites 50 μm to 1mm in diameter constitute an intermediate population between interplanetary dust particoles (IDPs) and meteorites, and represent almost the 80% of all the meteoritic mass (excluding rare, large impactors with mass m≥10exp11 Kg) accreting onto Earth. Deceleration in the Earth’s atmosphere causes frictional heatig in micrometeorites, as a function of the entry angle, mass and initial velocity of the particle.. The atmospheric entry of these large cosmic particles gives evidence that only those with very low geocentric velocities survive partially melted and unmelted without cvaporising, suggesting that the large micrometeorites arrive on Earth by non gravitational effects, as the Poynting- Robertson (P-R) effect and the solar pressure radiation, from asteroids of different belts and low-inclination comets. In a preliminary test study, wind blown Antarctic gross-particles (up to 300-400 micron) have been trapped during December 1994- January 1995 in collectors inside meteorological containers and aerosol samplers nearby Campo Icaro (74° 42’ 43’’S; 164° 06’ 58’’ E) in Anctartica. Mineralogical analysis show that the large micrometeorites are consipuously rare and the collected particles are consituted by single crystal fragments of feldspars, quartz, biotite, and amphibole as observed in order of abundance. A mechanism of concentration of comsic dust in polar regions by sedimentation precesses occurring into seasonal meltwater lakes on glaciers close to coastal regions, is thought to be a decisively more efficient mechanism than the eolian transport of these large meteorites.