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Every year, 5,200 tons of extraterrestrial dust fall to Earth.
This gentle rain of bits of comets and asteroids far outweighs larger meteorites that hit the planet, according to research to be published April 15 in the journal Earth & Planetary Science Letters. Only about 10 tons (9 metric tons) of larger space rocks land on Earth annually.
Despite the large quantities, it's hard to detect space dust or track its annual accumulation in most places due to precipitation that washes dust away. And in most places, dust originating on Earth swamps dust from space.
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But in Adélie Land, Antarctica, near the French-Italian Concordia research station, snowfall is very predictable and there is very little terrestrial dust. Over 20 years, French National Centre for Scientific Research (CNRS) physicist Jean Duprat and his colleagues have made six expeditions to the area to collect particles. The layers of space dust are well enough preserved in the region for researchers to estimate how much fell year after year.
Researchers dug out large trenches of snow and carried the snow layers in 44-pound (20 kilograms) barrels back to the laboratory at the research station, where they carefully melted the snow and collected the dust particles left behind. They then sorted the particles, removing contaminants like fibers from the researchers' snow gloves.
Extrapolating from the findings in central Antarctica, the researchers found that approximately 5,200 tons (4,700 metric tons) of these tiny particles, measuring between 30 and 200 micrometers in diameter, drop onto Earth each year. (For reference, a human hair averages about 70 micrometer in diameter.) That makes tiny particles the most abundant source of extraterrestrial material on Earth.
Because much of the space rock that crashes through Earth's atmosphere burns up, the researchers estimated the volume of dust in space that would result in that flux on the planet's surface. They gauged that about 15,000 tons (13,600 metric tons) of space dust initially enter the atmosphere each year, meaning only about a third reaches the ground. About 80% of the dust probably comes from comets known as Jupiter-period comets, the researchers wrote. These are comets with short orbits controlled by the influence of Jupiter's gravity. The other 20% of dust likely comes from asteroids.
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Understanding the flux of extraterrestrial material to Earth is important for many fields of astrophysics and geophysics, the researchers wrote, because these space rocks may have brought many elements to the planet. Some theories hold that elements and molecules originating from space rocks may have been crucial to the early development of life on Earth.
Stephanie Pappas is a contributing writer for Live Science, covering topics ranging from geoscience to archaeology to the human brain and behavior. She was previously a senior writer for Live Science but is now a freelancer based in Denver, Colorado, and regularly contributes to Scientific American and The Monitor, the monthly magazine of the American Psychological Association. Stephanie received a bachelor's degree in psychology from the University of South Carolina and a graduate certificate in science communication from the University of California, Santa Cruz.
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