Micrometeorites from Antarctic ice and snow
The cleanest, best-preserved micrometeorites come from the polar ice sheets, where there is almost no Earthly dust to hide them and the cold stops them from weathering.
In the middle of Antarctica, almost the only solid specks falling with the snow are from space. Scientists melt huge amounts of ice and snow, filter the water and pick out the micrometeorites under microscopes. Other teams sweep up dust trapped in cracks on bare Antarctic mountaintops, where it has gathered for hundreds of thousands of years.
Key facts
- Why Antarctica
- Very little local dust, deep cold, and ice layers of known age
- Main methods
- Melting blue ice, melting dated snow, filtering a station's water well, sweeping rock traps
- Best for
- Fresh, fragile, unmelted particles, including ultracarbonaceous ones
- Who may collect
- Only scientific programmes; Antarctic material is protected by international agreement
Why the poles are perfect
On most of the Earth, space dust is a few grains in a mountain of soil, pollen, soot and industrial particles. The interior of Antarctica is different. It is a high, cold desert covered by ice, hundreds of kilometres from bare rock, the sea or any town, so almost nothing else falls with the snow. The cold also preserves the particles: glass, clays and organic matter that would be destroyed in a few thousand years elsewhere can survive for hundreds of thousands of years in the ice.
Ice and snow are laid down in yearly layers that can be dated, so a sample of known age and known area can be used to measure how fast dust is falling, and how that rate has changed.
Greenland first
The modern era of polar collecting began in the 1980s in Greenland, where a French physicist, Michel Maurette, and colleagues gathered dark sediment from the bottoms of meltwater lakes and holes on the ice sheet. Meltwater had concentrated the dust of many years, and it contained large numbers of micrometeorites. The Greenland material was valuable but somewhat weathered by the water, which led the team to look for cleaner ice.
Melting blue ice
From the late 1980s, Maurette's teams worked on blue ice near the coast of Antarctica. Blue ice is old ice exposed at the surface where wind strips away the snow. They pumped hot water into the ice to melt pockets, then pumped the meltwater through fine filters. By the early 1990s they had processed around 100 tonnes of ice and recovered large numbers of micrometeorites larger than 0.05 mm, collections that showed for the first time how common unmelted particles are.
The South Pole water well
The US research station at the South Pole gets its drinking water by melting a deep chamber in the ice beneath it. As the well grew, it melted ice laid down as snow several centuries earlier, and every particle in that ice settled to the bottom. In the 1990s a team led by Susan Taylor, an American scientist working on cold-regions engineering, lowered a remotely controlled vacuum to the floor of the well, about 100 m below the surface, and filtered the sediment. The South Pole water well collection, reported in 1998 and 2000, held particles from about 0.05 to 2 mm, and because it captured nearly everything in a known volume of ice, it gave one of the first reliable measurements of the micrometeorite flux at the ground.
Clean snow at Dome C
The cleanest collections come from the high plateau, near the French–Italian station at Dome C, more than 1,000 km inland and over 3,000 m above sea level. Since 2000, a team led by Jean Duprat and Cécile Engrand has dug trenches into the snow, cut out blocks from layers a few metres deep, melted them in clean conditions and filtered every particle. Snow falls slowly there, so each layer represents a few decades of dust.
These samples have yielded beautifully preserved unmelted particles, the first ultracarbonaceous micrometeorites, and in 2021 the best measurement yet of how much dust reaches the ground: about 5,200 tonnes a year. See how much falls.
Rock traps in the mountains
Where Antarctic mountains poke through the ice, the wind blows away snow and leaves bare rock. On some summits in the Transantarctic Mountains, Italian and French researchers, including Luigi Folco and Pierre Rochette, found that fine sediment trapped in cracks and hollows in the bare rock is rich in micrometeorites. Because these surfaces have been exposed for a very long time, the traps hold dust gathered over perhaps hundreds of thousands to a million years or more, including unusually large particles, some close to 2 mm across, which are too rare to find in younger samples. The same traps also hold microtektites: tiny glass beads splashed out by a giant impact in south-east Asia about 0.8 million years ago and carried thousands of kilometres.
Other Antarctic collections
Japanese teams have collected micrometeorites from surface snow and ice near their inland stations, and Belgian, British, Chinese and other groups have worked at sites across the continent. Each site samples a different period and size range, so together they let scientists compare the dust of recent decades with that of hundreds of thousands of years ago.
Can I collect them?
No. All Antarctic samples are collected by national scientific programmes under the Antarctic Treaty system, which protects the continent's environment and treats the material as a resource for science. If you want to search for micrometeorites yourself, the place to start is much closer to home: see search for micrometeorites yourself.
Did you know?
A collection that filled only a small vial, about a fifth of a gram of space dust from the South Pole well, was at the time the largest collection of micrometeorites ever made from the ground.
Some Antarctic micrometeorites have spent so long in the ice that they record the dust that fell before the last several ice ages.
Blue-ice areas also concentrate ordinary meteorites, which is why Antarctica has yielded more meteorite finds than any other continent.