Mountains of space dust fall on Earth each year
T“Dust originating on Earth swamps dust from space”
his gentle rain of space dust consists of bits of comets and asteroids, a total of 4,700 tonnes, far outweighing larger meteorites that hit the planet. Only about nine tonnes 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. But in Adélie Land, Antarctica, near the French-italian Concordia Research Station, snowfall is very predictable and there is very little terrestrial dust. Over the last 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 20-kilogram 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 fibres from the researchers’ snow gloves. Extrapolating from the findings in central Antarctica, the researchers found that approximately 4,700 tonnes of these tiny particles, measuring between 30 and 200 micrometres in diameter, drop onto Earth each year – for reference, a human hair averages about 70 micrometres 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 13,600 tonnes of space dust must initially enter the atmosphere each year, meaning only about a third of it reaches the ground. About 80 per cent of the dust probably comes from comets known as Jupiter-family comets. These are comets with short orbits controlled by the influence of Jupiter’s gravity. The other 20 per cent of dust likely comes from asteroids. Understanding the flux of extraterrestrial material to Earth is important for many fields of astrophysics and geophysics 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.