London, April 9 (IANS) Every year, over 5,000 tonnes of extraterrestrial dust fall to Earth each year, scientists have determined.

Our home planet encounters dust from comets and asteroids. These interplanetary dust particles pass through our atmosphere and give rise to shooting stars. Some of them reach the ground in the form of micrometeorites.

Micrometeorites have always fallen on our planet. These interplanetary dust particles from comets or asteroids are particles of a few tenths to hundredths of a millimetre that have passed through the atmosphere and reached the Earth's surface.

An international programme conducted for nearly 20 years by scientists from the French National Centre for Scientific Research (CNRS), the Universite Paris-Saclay and the National museum of natural history with the support of the French polar institute, has determined how much of these micrometeorites reach the ground.

To collect and analyse these micrometeorites, six expeditions led by CNRS researcher Jean Duprat have taken place over the last two decades near the Franco-Italian Concordia station (Dome C), which is located 1,100 kilometres off the coast of Adelie Land, in the heart of Antarctica.

Dome C is an ideal collection spot due to the low accumulation rate of snow and the near absence of terrestrial dust.

These expeditions have collected enough extraterrestrial particles (ranging from 30 to 200 micrometres in size), to measure their annual flux, which corresponds to the mass accreted on Earth per square metre per year.

If these results are applied to the whole planet, the total annual flux of micrometeorites represents 5,200 tonnes per year, according to the study which will be available in the journal Earth & Planetary Science Letters from April 15.

This is the main source of extraterrestrial matter on our planet, far ahead of larger objects such as meteorites, for which the flux is less than ten tonnes per year.

A comparison of the flux of micrometeorites with theoretical predictions confirms that most micrometeorites probably come from comets (80 per cent) and the rest from asteroids.

The results could help scientists better understand the role played by interplanetary dust particles in supplying water and carbonaceous molecules on the young Earth.

--IANS gb/ash