As our planet orbits the sun, it is thrown through clouds of extraterrestrial dust and several thousand tons of that material actually reach the Earth’s surface each year, new research suggests.
For three summers in Antarctica over the past two decades, researchers have collected more than 2,000 micrometeorites from three snow pits they had dug. The extra-workers of this meager sample to the rest of the world, small pebbles in space account for a whopping 5,200 metric tons of weight gain each year, researchers report in the scientific charts of Earth and Planets on April 15th.
Much of Antarctica is the perfect repository for micrometeorites because there is no liquid water to dissolve or otherwise destroy them, says Jean Duprat, a cosmochemist at the Sorbonne University in Paris (SN: 29/05/20). However, collecting the samples was not an easy task.
First, Duprat and colleagues had to dig two meters or more to reach layers of snow deposited before 1995, the year researchers installed a field station at an indoor site called Dome C. They then used ultraclean tools to collect hundreds of pounds of snow, melt it and sift the small treasures of the icy water.
J. Duprat, C. Engrand, CNRS Photothèque
In all, the team found 808 spheres that had partially melted as they passed through the Earth's atmosphere and another 1,280 micrometeorites that showed no such damage. The particles were 30 to 350 micrometers wide and together weighed only fractions of a gram. But all micrometeorites were found within three areas totaling a few square meters, the lowest fraction of the Earth's surface. Assuming that space dust particles are as likely to fall in Antarctica as anywhere else, it allows the team to estimate the amount of dust that has fallen on the entire planet.
The team’s findings “are a wonderful complement to previous studies,” says Susan Taylor, a geologist at the Cold Regions Research and Engineering Laboratory in Hanover, N.H., who did not participate in the new study. He said Duprat and his colleagues found many small things that would dissolve elsewhere.
Researchers estimate that about 80 percent of micrometeorites originate from comets that pass much of their orbits closer to the sun than Jupiter. Much of the rest probably stems from collisions of objects in the asteroid belt. Together, these small particles deliver between 20 and 100 tons of carbon to Earth each year, Duprat and colleagues suggest, and may have been an important source of carbon-rich compounds such as amino acids early in Earth's history (SN: 12/4 / 20).