Urban gutters hide Earth's cosmic dust: rooftop micrometeorites revealed
Earth is continually showered with extraterrestrial material, mostly micrometeorites smaller than sand; estimates place about 5,200 tonnes reaching the surface annually (with ~15,000 tonnes entering the atmosphere in total), while larger meteorites are far rarer. Urban rooftops have become a surprising source of recent micrometeorites thanks to citizen scientists and researchers; distinguishing genuine cosmic grains from urban debris requires lab analysis of chemical signatures rather than magnetism. Rooftop collections provide timely reference samples that complement Antarctic and deep-sea records, showing cities have always collected space dust—it's just now easier to find real grains amid the noise.