Antarctica is the go-to spot to collect cosmic dust—the tiny grains of space rock that date back to our planet's infancy. These specks from space are challenging to find and previously thought impossible to separate from the chaos of urban debris.
But a new study, recently published in the journal Geology, suggests that cosmic dust may be found closer to home. Matthew Genge from Imperial College London and amateur Norwegian scientist Jon Larsen combed through 660 pounds of gunk collected from gutters in Oslo, Paris and Berlin, finding 500 particles of cosmic dust, according to a press release.
“We’ve known since the 1940s that cosmic dust falls continuously through our atmosphere, but until now we’ve thought that it could not be detected among the millions of terrestrial dust particles, except in the most dust-free environments such as the Antarctic or deep oceans,” Genge tells New Scientist. “The obvious advantage to this new approach is that it is much easier to source cosmic dust particles if they are in our backyards.”
JoAnna Wendel at Earth & Space Science News points out that there several educational websites that encourage people to collect debris from their gutters. They say that anything spherical or magnetic could be a micrometeorite. But researchers have poo pooed that idea and have long thought it was impossible to distinguish between space dust and industrial pollution.
But Larsen was not convinced, Wendel reports. For six years, he collected urban dust and debris from cities around the world, sifting through hundreds of pounds of dust and looking at 40,000 bits through the microscope. One thousand of those were convincing enough to put under a scanning electron microscope. In February 2015, he finally found one particle with the telltale marks of a micrometeorite. That’s when he approached Genge about his find.
“When Jon first came to me I was dubious,” Genge says in the press release. “Many people had reported finding cosmic dust in urban areas before, but when they were analyzed scientists found that these particles were all industrial in origin.”
But this urban space speck convinced him. So he helped Larsen refine his hunting techniques. Since then, Larsen has recovered 500 of the particles. They are slightly larger than average, measuring about 0.3 millimeters compared to the usual 0.01 millimeters, according to New Scientist. Analysis suggests that they likely melted while hurtling through earth’s atmosphere at 12 km per second, the fastest any dust particle has traveled on Earth.
These urban micrometeorites also suggest that the dust making it to Earth has changed over time, according to the press release. Dust captured in Antarctic ice is much more ancient, accumulating over the last million years. And unlike these minute particles, the urban cosmic dust contains feather-like crystals. The urban particles are, however, similar to dust that has fallen since Medieval times.
The difference in size is probably caused by slight changes in the orbits of Earth and Mars, Genge explains in the press release. This change affects the gravitational pull on the particles, causing them to come in faster and heat up more, which alters their size and shape. Those changes, he says, are important to understand if cosmic dust is used to reconstruct the geologic history of the solar system.
While the research is interesting and Larsen’s dedication is impressive, Susan Taylor, a research scientist at the U.S. Army Cold Regions Research Laboratory tells Wendel it's unlikely that she and other scientists will start scouring local gutters anytime soon. Finding 500 particles in 600 pounds of gunk is slow going, compared to the thousands of micrometeorites she can pull out of a single bore hole in Antarctica.
Yet, it's still fun to consider that there's more to the dust in the street than industrial pollution—you could be looking at some specks from space.