Forty-thousand tons of cosmic dust falls to Earth each year. These particles that have been around since the formation of our solar system have been found for the first time on rooftops in three of the world’s major cities.
These particles are tiny, roughly around 0.01 millimetres in size, and have been falling to Earth since it was formed billions of years ago. Analyzing their chemical and mineral content can tell scientists about how the early solar system has evolved. Most dust is collected by scientists from the frozen wastes of places like Antarctica, as it was thought too difficult to unearth these little time capsules in urban debris.
For a new study, Dr. Matthew Genge from Imperial College London teamed up with Jon Larsen, an amateur scientist from Norway, to sift through 300 kilograms of sediment that was trapped in gutters on roofs in Paris, Oslo and Berlin. Cosmic dust particles contain minerals that make them magnetic, so they used magnetism to separate the particles under the microscope, finding 500 of them in the debris. The samples analysed show the comparatively big cosmic dust that have recently, in geological terms, fallen on Earth.
In the infrared image at the top of the page, stellar winds from a giant star cause interstellar dust to form ripples. This cosmic dust—which contains oxygen, carbon, iron, nickel, and all the other elements—out there, and eventually some of it finds its way into our bodies. (NASA, JPL-CALTECH)
In 2011, Larsen contacted Genge to say he believed it was possible to find to find cosmic dust particles in an urban landscape such as cities. “When Jon first came to me I was dubious. Many people had reported finding cosmic dust in urban areas before, but when they were analysed scientists found that these particles were all industrial in origin,” said Genge.
“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. The obvious advantage to this new approach is that it is much easier to source cosmic dust particles if they are in our backyards.”
In the study, which is published in the journal Geology, the team report that the cosmic dust particles that they recovered from roof tops are larger than other particles previously recovered, at around 0.3 millimetres. Based on the particles’ size, the researchers’ analysis suggests they were formed by melting during atmospheric entry at speeds of around 12 km per second. Dr Genge says this would make them the fastest moving dust particles found on Earth.