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takyon writes:

Scientists have discovered significant numbers of "large" micrometeorites collected from the debris found in urban rooftop gutters:

For years, amateur astronomers have been suggesting that microscopic, spherical particles collected from their roofs are actually tiny meteorites, the dust that formed our Solar System fallen to Earth. Scientists took the claim at face value but ended up being the downers again, at least initially. [...] One of those amateurs is a Norwegian artist and jazz guitarist named Jon Larsen, who created a group called Project Stardust. Larsen managed two impressive feats to get the issue revisited. One, he convinced people in Oslo to gather materials from their roof gutters (although, oddly, one sample also came from Paris). And not just a few—material came in from buildings that collectively possessed 30,000 square meters of roof.

The second feat was that Larsen got a small international team of scientists (Belgian and UK) to take this seriously. Faced with about 300kg of roof debris, the authors separated the material using a combination of magnets and physical shape—micrometeorites are spherical because they melt during atmospheric entry and are shaped by the air. From that 300kg, the researchers isolated 500 particles, all just a few hundred micrometers across, that looked like they were micrometeorites. Forty-eight of them were chosen for detailed analysis. All 48 of them appear to be genuine micrometeorites.

An urban collection of modern-day large micrometeorites: Evidence for variations in the extraterrestrial dust flux through the Quaternary (open, DOI: 10.1130/G38352.1) (DX)

Original Submission