Every day, the Earth is showered with about 100 tons of cosmic dust, sub-millimeter mineral particles that have been floating around since before our solar system formed 4.6 billion years ago. They enter Earth's atmosphere at speeds of at least 7 miles per second, and despite their small size, they account for most of the extraterrestrial material on Earth by weight.
Since the astronomer Fred Whipple coined the term 'micrometeorite' in 1950, hundreds of samples of cosmic dust have been collected all over the world. All of these samples are collected at pristine sites far away from human activity, such as by drilling into the polar icecaps or using a magnetic sled to dredge the ocean floor. But last year Matthew Genge, a planetary scientist at Imperial College London, joined forces with Jon Larsen, a professional Norwegian musician moonlighting as an amateur scientist, who has been hunting and photographing micrometeorites for nearly a decade and recently found the first micrometeorite in an urban environment.
As detailed in a paper published last December in Geology, Genge and Larsen collected some 300 kilos of dust from rooftops in Paris, Berlin and Oslo for their project. Using magnets to separate the cosmic dust from the terrestrial, the pair managed to find some 500 micrometeorites in their dust collection. Now, Larsen has collected these specimens into a forthcoming book of truly stellar photography called In Search of Stardust.
I caught up with Larsen to see what the process of hunting for cosmic dust in some of the world's largest cities is like, and why he and Genge succeeded where many others have failed.
Motherboard: How do you photograph such small objects with so much detail?
Jon Larsen: Parallel with the search for the micrometeorites I have worked with Jan Braly Kihle to construct a photographic instrument to document the micrometeorites in hi-res color. It has taken us several years, but with a combination of already existing lenses and an Olympus camera, custom built adaptations and new inventions both in hardware and software we now have an instrument that allows us to take color photos of micrometeorites with up to 3,000 times magnification. This allows us to see these small grains from space like nobody has seen them before. Up until now micrometeorites from Antarctica have been documented via SEM section images: black and white pictures full of structural details, but ofter rather misleading as to what micrometeorites actually look like.
Was it easier to find micrometeorites once you knew what you were looking for?
Today I find them everywhere. The problem was that no one had documented what micrometeorites look like. All micrometeorites from the Antarctic collections had been molded in resin and grinded down to a section which had been analysed, but these black/white images from the electron microscope show a very confusing picture, and nothing like what micrometeorites really look like, when you encounter them in the urban dust.
How did you ensure these were actually extraterrestrial, rather than industrial?
At the lecture at the University of Bergen the news about the new discovery was revealed, and the professors asked Genge: "But how do you know that this is a micrometeorite?" and Dr. Genge answered superbly, "Because this is what they look like." I have studied the morphology of nearly 1,200 micrometeorites, and that is still the answer, which was a big surprise to all of us. The micrometeorites turn out to have a distinct and characteristic appearance, like nothing else down on Earth. However, we've had to do all the various analyses in order to confirm the extraterrestrial origin.
What can urban micrometeorites tell us that cosmic dust found in Antarctica or on the bottom of the ocean cannot?
The cosmic dust is the oldest matter there is, and even if we still don't know exactly where the micrometeorites are coming from, we can learn a lot about the earliest stages of our solar system—how the planets and the Sun were formed, and deep down who we are as humans because Joni Mitchell was right: we are stardust! It turns out that unmelted micrometeorites contain 12-15 percent water, and it is a mystery where the water on Earth has come from. The French scientist Dr. Michel Maurette has done the math and proposed that the water on Earth has been delivered by the micrometeorites. Furthermore, unmelted micrometeorites contain complex organic molecules, like amino acids. The second big question is whether these organic compounds participated in the formation of life on Earth? And finally, if cosmic dust delivers water and complex organic molecules to young planets and the cosmic dust is omnipresent in the Universe, is this what the cosmic dust is doing on the many exoplanets that are being discovered?
How did you gain access to all these roofs during your hunt? Did people look at you weird when you told them you were hunting for particles of dust?
Norway is a very open society, so when I ask people for permission to take a dust sample from their roof they say 'OK, go ahead, but be careful.' But not so in France, Spain or the US, unfortunately. I travelled around the southwest US in February, and asked everywhere, but everybody said 'no'. Lucky for me it was prearranged by Michael Zolensky at NASA's Johnson Space Center to enter several roofs there, and we found lots of amazing micrometeorites. Ironically, after having been shown NASA's incredibly clean lab for the examination of the Wild 2 comet particles, the next day we went up on the dirty roof and found basically the same particles.
Is this something that anyone can do at home? What tools would an amateur micrometeorite hunter need?
Yes, indeed. All you need is access to a large skyward facing area, like a flat roof—most types will do, but the very best are types of vinyl roofs which create no additional particles from itself. Then, on a dry day you sweep the loose particles together (the wind and rain have already done most of the job for you) and extract the magnetic particles with a magnet. Then you rinse the particles with plenty of water and perhaps a little diswasher soap, and wait until the particles dry. Then I extract the magnetic ones once again, and screen for size—and look at the particles in the 200-400 micrometer range under a binocular microscope. By searching for the surface textures described in the book, and eliminating the many types of industrial particles, you will find the micrometeorites: the most exotic particles in the Solar system.
This interview has been edited for clarity and length.