We have known for some time that the earth is under a constant rain of space dust and that it is abundant. However, given the microscopic size, it was very difficult to get an accurate estimate of the quantity.
Such micrometeorites are not larger than a fraction of a millimeter, such as the space outpourings of comets and asteroids.
After two decades of collecting the goods in Antarctica, an international team of scientists now has a number: annually about 5,200 tons of micrometeorites smaller than 700 micrometers (0.7 millimeters).
According to them, it makes micrometeorites the largest source of extraterrestrial material produced on the earth’s surface.
It’s actually quite an achievement. The earth’s atmosphere is filled with dust, of all kinds. A study last year found that about 17 million tons of coarse dust blows into the atmosphere at any one time.
To keep this ‘background’ dust to a minimum, the team turned to Antarctica at the Concordia station in Dome C. Fertilizer is quite absent there, and the snow collection is low, meaning the snow that is already there , can be fused to obtain the rate of decrease of micrometeorite in the region.
Micrometeorites of Antarctica. (Rojas et al., EPSL, 2021)
In six expeditions over the course of 20 years, the researchers did just that. They identified a total of 1,280 unmelted micrometeorites and 808 cosmic spheres (molten space rock) below 350 micrograms in mass, which enabled them to calculate the rate at which these particles rain on the surface.
According to their calculations, extrapolated all over the world and if we assume that the rain is evenly distributed, about 1600 tons of micrometeorites and 3,600 tons of cosmic spheres reach the surface each year. This is a total of 5,200 tons per year.
The next part of the research was an analysis of the substance to determine its origin, based on the density of the grains. Lower density and higher porosity indicate a cometic origin, and higher density and lower porosity indicate a meteorite origin.
From this, the team extrapolated that about 80 percent of the cosmic matter that reaches the Earth’s surface is ejected from comets as they zoom in on their orbits – a number that is consistent with previous estimates of the comet’s input into space dust on Earth.
However, the models of the team also showed that the total mass of cosmic dust input before the atmosphere is about 15,000 tons. The reason for this difference is not clear, but there are some important options.
The one is that a significant portion of the substance avoids us detecting it. The other is that some of the dust is removed from the atmosphere. A third could be that there is significantly less dust in space around the earth than we think.
The researchers determined what it is, can help us better limit the role of cosmic matter in the delivery of water molecules and carbon to the earth, in the early days of the solar system – to provide again pieces of the puzzle that the rise of life itself.
The team’s research was published in Earth and Planetary Science Letters.