Space Grain

[Image: A micrometeorite, photographed by Donald Brownlee, University of Washington].

A paper published last month in Geology reported “the discovery of significant numbers (500) of large micrometeorites (>100 μm) from rooftops in urban areas”—or “cosmic dust grains,” in the words of New Scientist, that have been “found on city rooftops for the first time.”

Although the samples were “collected primarily from roof gutters in Norway,” according to the original paper, their presence there “demonstrates that, contrary to current belief, micrometeorites can be collected from urban environments.” That is, the dust of ruined cosmic objects can be found intermixed with autumn leaves, cigarette butts, and brake pad dust, perhaps even accumulating on your bedroom window sill.

[Image: Gorgeous photograph of a micrometeorite by Matej Pašák].

Of course, it has long been possible to sample urban areas for micrometeorites, so this is not entirely new.

What’s fascinating, nonetheless, is that these micrometeorites are most likely to have arrived on Earth within the past six years, the study points out, but their size is notably larger than the average sample of micrometeorites from the recent geological record, indicating “variations in the extraterrestrial dust flux” on the scale of 800,000 years.

As New Scientist points out, this means that larger cosmic shifts can be deduced from the size and shape of these grains:

The differences [in size] may be linked to changes in the orbits of planets such as the Earth and Mars over millions of years, [researcher Matthew Genge] says. Resulting gravitational disturbances may have influenced the trajectory of the particles as they hurtled through space. This in turn would have an effect on the speed at which they slam into the Earth’s atmosphere and heat up.

“This find is important because if we are to look at fossil cosmic dust collected from ancient rocks to reconstruct a geological history of our solar system, then we need to understand how this dust is changed by the continuous pull of the planets,” Genge says.

Something’s changing in our local cosmic-dust environment, in other words, and evidence of this shift is slowly collecting on our roofs and sidewalks, accumulating in our gutters and sills.

(Conceptually related: War Sand).

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