Searching for stardust: How to find micrometeorites in your gutters

by NEW YORK DIGITAL NEWS


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Dust left over from the birth of the solar system is constantly falling to Earth

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IT WAS a warm summer morning in the countryside near Oslo and Jon Larsen decided to have breakfast outdoors. He carefully wiped down the white plastic table on his patio and went inside to collect his meal. Then, as he sat down to eat, he noticed a tiny black speck on the table. “It was glittering in the sun,” he says. “I thought, wow, what is this?”

That was 2009. Fast forward a decade and Larsen has managed to pull off something many thought impossible. He has shown that merely by scouring ordinary urban spaces, you can find your own micrometeorites – tiny specks of extraterrestrial dust that have been floating around since the birth of the solar system, billions of years ago. These days, his collection comprises more than 3000 specimens and he boasts a large fan base of urban space-dust hunters.

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I had heard a little about Larsen’s work and got the impression that following in his footsteps wouldn’t be too difficult. All I needed, it seemed, was some dirt from an undisturbed roof and a microscope. Could I really find my own stardust? I was about to find out.

A meteorite is a chunk of debris left over from the early years of the solar system that has survived passage through our atmosphere and crashed to the ground. They are nearly all chunks that have broken off asteroids orbiting between Mars and Jupiter, and they contain an unblemished record of conditions in the early solar system – information we have used to understand how the planets formed.

Micrometeorites are a lot smaller, obviously. They must be less than 1 millimetre to qualify. But they are also more mysterious. “If you grind up a meteorite you don’t get micrometeorites,” says Cecile Engrand at Paris-Saclay University in France. Micrometeorites, unlike their bigger cousins, seem to have not been heated at all after they formed at the birth of the solar system and so represent its most primitive matter.

We don’t know for sure whether they come from the furthest reaches of the asteroid belt or from comets. But we do know that, while most regular meteorites are bone dry, the majority of micrometeorites contain water and carbon-containing compounds that are the building blocks of life. One hypothesis holds that it was a slow, steady dusting of these particles that helped fill Earth’s oceans. “To me, it’s a wonder that you can look at something so tiny under a microscope and use it to understand stuff to do with the whole solar system,” says Engrand.

Finding space rocks often involves an expedition to a desert, where the meteorites stand out against the plain backdrop. Even there, it isn’t easy. Sizeable meteorites are vanishingly rare. Smaller meteorites are more common though, and when you get down to micrometeorite scales, we are talking about a constant sprinkling. Estimates suggest that around 100 tonnes of these particles fall to Earth each day, which works out as roughly two specks of dust per square kilometre per second. That means there is a good chance one has landed on any given roof.

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A selection of micrometeorites, each less than 1 millimetre in diameter, from the collection of Jon Larsen

Jon Larsen

Searching for them has always been considered a futile exercise, largely because of the sheer volume of terrestrial dust you would have to wade through. It is like finding a needle in a whole barn of haystacks. Matthew Genge at Imperial College London studies micrometeorites recovered in remote places, such as Antarctica, where terrestrial dust is barely present. He says hobbyists routinely write to him claiming to have found the stuff, but they pretty much never have.

“Estimates suggest around 100 tonnes of micrometeorites fall to Earth each day”

Larsen wasn’t the most obvious candidate to succeed where so many others have failed. He has had an amateur interest in geology his whole life, but he made his living as one of Norway’s best-known jazz guitarists (he has recently retired, but Hot Club de Norvège, the band he founded in 1979, is still going strong). Yet he describes himself as obsessive, and after his interest was piqued by the sudden appearance of the speck on the breakfast table, there was no turning back. “I started thinking: there’s two truckloads of dust coming in every day and none of it can be found?” he says. “That’s very strange.”

Book of dust

While touring with his band, Larsen began a curious habit. In each new city, he would collect samples of dust and pick through it under a microscope. The trouble was, he had no idea what he was looking for. The few published pictures of micrometeorites were grainy black-and-white images in scientific papers. These suggested he should look for black spheres about 1-millimetre wide, but there were lots of things that fit that description in the detritus he collected and they couldn’t all be from space.

Larsen reasoned that various sorts of earthly dust from industrial processes, the environment and so on ought to be present in different amounts depending on location. Industrial cities might have more bits of dust created from welding, for instance. But cosmic dust ought to appear in the same amounts everywhere. So he began a systematic survey and, over the course of seven years, identified the 75 most common types of terrestrial dust.

Whatever didn’t fit into these categories was probably the space dust. He began sending pictures of this stuff to Genge in London. “To begin with, I just wanted him to go away,” says Genge. But Larsen was persistent. The particles he was finding were typically rounded and black with a kind of shiny, heavily grooved crust. That made sense because the passage of micrometeorites through the atmosphere often melts the particles and the rushing air moulds their surface into tiny undulations.

Eventually, Genge was persuaded to analyse the chemical composition of the dust and, in 2015, the pair announced that they had indeed found the first urban micrometeorites.

Now it was my turn to find some of this wondrous space dust. I borrowed a ladder and climbed up to reach my roof guttering. Then I used a garden trowel to scrape its contents into plastic sandwich bags. The weather had been fine, so it was mostly dry, dusty stuff and a few clumps of moss that the magpies had broken off the tiles. It wasn’t the most glamorous 15 minutes of my life, but somewhere amid the moss, feathers and dirt could be a minuscule cosmic prize.

On the Trail of Stardust, Larsen’s guidebook for stardust hunters, explains that the next step is to separate your regular dust from any cosmic stuff. To begin, I emptied my bag of roof muck into a plastic bowl, added water and washing up liquid and then stirred. I picked out the stuff that floated and, once the solids had settled at the bottom, decanted the brown water. After repeating this a few times, I was left with a dish of clean, tiny rocks.

I put these pieces through an old tea strainer to get rid of the larger chunks. Finally, I picked up a powerful magnet I had bought online, covered it in a plastic bag, stirred it around in the dust and transferred the magnetic stuff into a white bowl. This is a crude tactic because not every micrometeorite is magnetic, but it massively reduces the volume of dust you are working with.

The next step is to hunt through your dust grain by grain. I bought a cheap USB microscope and started searching. It is a beguiling world down there. Magnified 60 times, some specks look like pieces of multicoloured popcorn or dark, spiky stars. Others are translucent gems of many colours; red, blue and delicate green.

I knew to look for rounded black beads. But I’ll level with you: this stage nearly broke me. I spent at least 7 hours going through the dust. Sometimes, I would find a promising-looking speck only to lose it again. On several evenings, my wife had to explain that there were more important things to do right now, like read our children a bedtime story.

Eventually, I found and photographed seven pieces that looked promising. The only sure way to know if you have discovered a micrometeorite is to analyse its chemistry, but Larsen is such an expert that he can normally tell just by looking. When I sent him my photos, he offered a good-natured chuckle. He couldn’t see any convincing signs that these specks came from space.

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The beauty of micrometeorites is revealed under the microscope

Jon Larsen

I had thought that meteorite hunting would be easy and cheap. My magnet, USB microscope and other bits and pieces had collectively cost less than £30, but Larsen told me I would do well to get hold of some lab-grade sieves to isolate grains between 0.2 and 0.4 millimetres in size. This is where the majority of micrometeorites are hiding, he says, so the sieves significantly reduce the time it takes to find them. You also really need a binocular microscope to see the surface texture of the particles, which is the best way to identify those of a cosmic origin.

I am yet to find my own space dust – but I did track down a man who has. I got in touch with Jens Metschurat, a student at Clausthal University of Technology in Germany. He has been interested in hunting micrometeorites since he was a child, but his search stepped up a gear when he came across Larsen’s work. In three months using Larsen’s methods, Metschurat says he has found eight particles, one of which is more than 0.5 millimetres long – a giant among micrometeorites. So clearly, it can be done.

For his part, Larsen is working on his magnum opus, a 300-page book called Starhunter. He is also continuing his searches. What excites him now, he says, is that by sheer volume of discovery, he is starting to find unusual types of micrometeorites. The other day, he came across one that contained a lot of the rare element scandium, and he has found others with carbon-based molecules, the same stuff that forms the basis of all living things.

“I spent at least 7 hours sifting through a bowl of dust – this nearly broke me”

You might be wondering what happened to the speck that started it all, the one that fell on Larsen’s breakfast table. Well, not knowing how best to store microscopic particles, he put it in a matchbox and it got lost. I take a certain comfort from that story. It shows that even the best stardust hunters can come from humble beginnings.

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