NEW CALIBRATION OF THE MICROMETEOROID FLUX ON EARTH

Mass accretion rate on Earth is an important tool to discriminate the extraterrestrial nature of particles or isotopes found in different environments on the ground. In this context, the knowledge of the micrometeoroid flux arriving in our atmosphere is a key parameter and it needs to be calibrated. We provide a new calibration of the flux of submillimeter particles impacting the Earth in the mass range from 10(-9) to 10(-4) g, derived by computing a specific scaling law for impact craters on the Long Duration Exposure Facility (LDEF). We use the hydrocode iSALE to calculate the outcome of impacts on LDEF, adopting realistic impact velocities for dust particles derived from the numerical integration of their trajectories assuming either asteroidal or cometary origin. We estimate a particle mass accretion rate of (7.4 +/- 1.0) x 10(6) kg yr(-1) if the Main Belt is assumed as the major source of dust, while it reduces to (4.2 +/- 0.5) x 10(6) kg yr(-1) if cometary dust dominates. These values agree with the estimates provided by independent measurements made on ice core and ocean sediments and based on the abundance of some elements in the samples.