Cosmic Dust Bunnies

One of many new micrometeorites found by © Project Stardust. Photo credit: Jan Braly/Jon Larsen. 

 Jon Larsen is a modern day renaissance man. He’s an accomplished guitarist, composer, and painter, but lately he’s been spending his time sweeping up and collecting dust on Norwegian rooftops. Why would an artist spend his or her free time this way? Normally the answer would probably be drugs, but instead of angel dust, Larsen is getting high on a much more far-out kind of star dust, “urban micrometeorites”. 

A dusty night sky during the Perseid meteor shower in 2015.
Photo credit: Scott MacNeill/Frosty Dew Observatory.

Larsen is the principal investigator for a research organization called Project Stardust in Oslo. His goal over the past few years has been to prove that micrometeorites can be found in urban settings (usually on large, flat roofs).

As the name implies, micrometeorites are microscopic cousins of meteorites. You may be more familiar with the visual spectacle produced by the entry of micrometeorites into our atmosphere—shooting stars. Micrometeorites started their life off as dust particles floating between planets in our Solar System. That dust is what remains of planet-forming processes that occurred as long as 4.5 billion years ago. Some of those dust particles wind up drifting into Earth’s orbit, streaking through the atmosphere, and coming to rest somewhere on the surface.

We’ve known for years that micrometeorites exist.

Researchers have historically found them in seemingly unlikely places, such as ocean floors and antarctic ice sheets. These particles often contain a significant amount of iron, and can be separated from other dust particles with the aid of a simple magnet. Until recently, many in the scientific community thought searching for micrometeorites in more developed cities would be a fruitless endeavor. Cities tend have a higher concentration of artificial dust particles that are also magnetic and usually sourced from industrial processes. With a very small amount of micrometeorites falling to Earth each year, artificial dust particles far outnumber anything that fell from space.

Micrometeorites come in many forms that distinguish them from artificial dust particles.
Photo credit: Jon Larsen. © Project Stardust

Larsen was not deterred by the challenge, and developed a method of discriminating between artificial and extraterrestrial dust particles. His search consisted of over one thousand field searches, which usually involved sweeping up dust on rooftops, separating out magnetic material, thorough washing, and using sieves to separate out different dust sizes. The remaining particles were observed under the microscope for features that are characteristic of micrometeorites— aerodynamic shapes, beads of iron-nickel alloys, unusual surface textures, and chemical compositions that are distinct from those found on Earth.

The identification of urban micrometeorites provides new insight into the variety of interplanetary dust in the Solar System. Most of these particles were deposited within the last century, while micrometeorites collected in Antarctica and on ocean floors may have been deposited over a much greater span of time. A "crowd-sourced" collection effort is also much cheaper, and can involve non-specialists around the globe. An ongoing program examining changes in micrometeorite compositions over time could lend some insight into the distribution of interplanetary dust in the Solar System. This information could be used to understand processes that may have occurred during the formation of planets over 4.5 billion years ago.

Jon Larsen can't get his mind out of the gutter, as he uses a powerful Neodymium magnet
 to pick up magnetic dust particles in Oslo, Norway.  Photo credit: Project Stardust.

A basic guide to collecting urban micrometeorites can be found on Project Stardust’s website, although you’ll need a very high resolution camera to photograph them yourself. You can also buy his book, In Search of Stardust, online. Even if you don't find any micrometeorites on your first search, at least it’s one more reason for you to finally get around to cleaning out your rain gutters!