We have known for a while that the Earth is under a constant shower of space dust, and that it is abundant. However, given its microscopic size, it was very difficult to get an accurate estimate of the amount.
Such micrometeorites are no larger than a fraction of a millimeter and are thrown off as dander from passing comets and asteroids.
After two decades of collecting the stuff in Antarctica, an international team of scientists now has a number: about 5,200 tons of micrometeorites smaller than 700 micrometers (0.7 millimeters), each year.
This, they said, makes micrometeorites the largest source of alien material delivered to Earth’s surface.
It’s quite an achievement actually. The Earth’s atmosphere is filled with all kinds of dust. A study from last year found that there are about 17 million tons of coarse dust blowing around in the atmosphere at any one time.
To minimize this ‘background dust’, the team turned to Antarctica at the Concordia station in Dome C. Terrestrial dust is virtually absent there and snow accumulation is low, meaning that the snow that is already there can be melted to melt. obtain the rate of micrometeorite decline in the region.
Micrometeorites from Antarctica. (Rojas et al., EPSL, 2021)
That is exactly what the researchers did in six expeditions over a period of 20 years. They identified a total of 1,280 unmelted micrometeorites and 808 cosmic spheres (molten space rock) with a mass of less than 350 micrograms, allowing them to calculate the speed at which these particles rain on the surface.
According to their calculations, extrapolated around the world and assuming that the rain is evenly distributed, about 1,600 tons of micrometeorites and 3,600 tons of cosmic spheres reach the surface every year. That is a total of 5,200 tons per year.
The next part of the study was an analysis of the dust to determine its origin based on the density of the grains. Lower density and higher porosity suggest origin of comets, and higher density and lower porosity suggest meteoritic origin.
From this, the team extrapolated that about 80 percent of the cosmic dust that reaches Earth’s surface is ejected by comets as they zoom past on their orbital travels – a number consistent with previous estimates of comet input to space dust on Earth.
However, the team’s models also showed that the total mass of cosmic dust entering the atmosphere before entering the atmosphere is about 15,000 tons. The reason for this discrepancy isn’t clear, but there are a number of important options.
One is that a significant portion of the dust eludes our ability to detect it. Another is that some of the dust is removed before it enters the atmosphere. A third could be that there is significantly less dust in space around the Earth than we think there is.
Figuring out which of these it is, the researchers said, could help us better narrow down the role of cosmic dust in delivering water molecules and carbon to Earth, in the early days of the solar system – and in turn bits of it. the puzzle to deliver that the origin of life itself.
The team’s research is published in Earth and Planetary Science Letters