The Solar System is dusty. Some of this dust could come from planets, some is the result of asteroids and comets. As Earth goes about its orbit, it regularly sweeps it. This material gives rise to meteor showers, and a small fraction of these can reach the ground as micrometeorites.
An international program has been working for 20 years to estimate how much material is raining down on our heads every year – they estimate about 5.2 million kilograms (11.5 million pounds) of micrometeorites. That’s equivalent to a two-and-a-half space shuttle's worth of extraterrestrial stuff landing on Earth every year. Larger meteorites make up about 10,000 kilograms (22,000 pounds) of space stuff getting to Earth.
The findings are reported in Earth & Planetary Science Letters. The micrometeorites are really tiny – the ones reported in this study were mostly between 30 and 200 micrometers. Given their size, it is unsurprising that it is difficult to work out just how much of them fall to the ground every year. The team, lead by scientists at the CNRS, the Université Paris-Saclay, and the National Museum of Natural History, went to a place where they could find one of the best places on Earth to do so: Antarctica
The Franco-Italian Concordia station is located in a region called Dome C, right in the heart of the southernmost continent. The area has a low accumulation of new snow and very little terrestrial dust, so space dust becomes easier to find and collect. The team performed six expeditions there, allowing them to estimate the yearly flux of micrometeorites.
The findings suggest that 80 percent of the micrometeorites come from comets, mostly Jupiter-Family comets. The remaining 20 percent comes instead from asteroids. The findings above 100 microns match the theoretical predictions for the amount of extraterrestrial dust we should be seeing. But below 100 microns, we see a lot fewer micrometeorites than predicted from the amount of dust there should be out there in the solar system at the distance that the Earth is from the Sun (1 Astronomical Unit – AU)
“This suggests several possibilities: the existence of highly fragile particles that would not be collected with the collection protocol in Dome C snow; fragmentation removal of a significant number of small particles before atmospheric entry; or that the actual amount of small interplanetary particles at 1 AU may be smaller than expected,” the authors wrote in the conclusion of the paper.
The uncertainties of this work can hopefully be improved in the future with different approaches to sample collections.