We have known for some time that the Earth is under a constant rain of space dust and that it is abundant. However, given its microscopic size, it was very difficult to obtain an accurate estimate of the amount.
Such micrometeorites are no larger than a fraction of a millimeter, spilled like space hair from passing comets and asteroids.
After two decades of collecting things in Antarctica, an international team of scientists now has a number: around 5,200 tons of micrometeorites smaller than 700 micrometers (0.7 millimeters) each year.
These, they said, make micrometeorites the largest source of extraterrestrial material delivered to the Earth’s surface.
It’s actually a pretty big achievement. The Earth’s atmosphere is full of dust of all kinds. A study last year found that about 17 million metric tons of coarse dust blows into the atmosphere at any given time.
To minimize this “background” dust, the team headed to Antarctica at the Concordia station at Dome C. The ground dust is almost absent there, and the snow accumulation rate is low, which means that the snow that already exists can melt. to obtain the micrometeorite rate decreases in the region.
Antarctic micrometeorites. (Rojas et al., EPSL, 2021)
In six expeditions over 20 years, researchers have done just that. They identified a total of 1,280 unmelted micrometeorites and 808 cosmic spheres (molten space rock) under 350 micrograms in mass, which allowed them to calculate the rate at which these particles rain at the surface.
According to their calculations, extrapolated around the globe and assuming that the rain is evenly distributed, about 1,600 tons of micrometeorites and 3,600 tons of cosmic spheres 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. The lower density and higher porosity suggest a cometary origin, and the higher density and lower porosity suggest a meteoritic origin.
From this, the team extrapolated that about 80% of the cosmic dust that reaches the Earth’s surface is evacuated from comets as they increase in their orbital travel – a number consistent with previous estimates of cometary entry into space dust on Earth.
However, the team’s models showed that the total mass of cosmic dust introduced before entering the atmosphere is about 15,000 tons. The reason for this discrepancy is not clear, but there are some major options.
One is that a significant proportion of the dust avoids our ability to detect it. Another thing is that some of the dust is removed before the atmospheric entry. One third could be the fact that there is significantly less dust in the space around the Earth than we think there is.
Finding out which of these is, say the researchers, could help us better constrain the role of cosmic dust in supplying water and carbon molecules to Earth in the early days of the solar system – providing in turn pieces of the puzzle that is the appearance of life itself.
The team ‘s research was published in Letters of Earth and Planetary Science.