We have known for a long time that the Earth is under a constant rain of space dust and that it is abundant. Given its microscopic size, however, it has been very difficult to obtain an accurate estimate of the amount.
These micrometeorites are no larger than a fraction of a millimeter, spilled like the space dandruff of passing comets and asteroids.
After two decades of collecting things in Antarctica, an international team of scientists now has a number: some 5,200 tons of micrometeorites smaller than 700 micrometers (0.7 millimeters) each year.
According to them, this makes micrometeorites the largest source of extraterrestrial material supplied to the earth’s surface.
In fact, it is quite a success. The Earth’s atmosphere is full of dust, of all kinds. A study last year found that about 17 million metric tons of thick dust is blowing into the atmosphere at any given time.
To minimize this “bottom” dust, the team headed to Antarctica at Concordia Station in Dome C. Earth dust is virtually absent and the rate of snow accumulation is low, which means that the snow that already exists can be melted to get the rate of micrometeorite falling in the region.
Micrometeorites of Antarctica. (Rojas et al., EPSL, 2021)
In six expeditions over 20 years, researchers did just that. They identified a total of 1,280 unmelt micrometeorites and 808 cosmic spheres (molten space rock) below 350 micrograms of mass, which allowed them to calculate the speed at which these particles rain on the surface.
According to his calculations, extrapolated around the world and assuming that rain is evenly distributed, approximately 1,600 tons of micrometeorites and 3,600 tons of cosmic spherules reach the surface each year. This represents a total of 5,200 tons per year.
The next part of the research was an analysis of the dust to determine its origin, based on the density of the grains. Lower density and higher porosity suggest a cometary origin, and higher density and lower porosity suggest a meteoritic origin.
From this, the team extrapolated that approximately 80 percent of the cosmic dust that reaches the Earth’s surface is expelled from comets as their orbital displacements increase, a number that matches previous estimates. from the cometary entrance to the Earth’s space dust.
The equipment models, however, also showed that the total mass of cosmic dust contributed before entering the atmosphere is around 15,000 tons. The reason for this discrepancy is unclear, but there are a couple of important options.
One is that a significant proportion of the dust eludes our ability to detect it. Another is that part of the dust is removed before atmospheric entry. A third could be that there is significantly less dust in space around the Earth than we think there is.
Finding out which of these, according to the researchers, could help us better limit the role of cosmic dust in supplying water and carbon molecules to Earth during the early days of the solar system, providing turn pieces of the puzzle that is the appearance of life itself.
The team’s research has been published in Earth and Planetary Science Charts.