The Hidden Treasures on Your Roof
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Hello, and welcome back to Everyday Science.
Have you ever seen a shooting star? Living in London with its light pollution, I don’t usually have much luck at spotting them, even when I stay up late at night to watch the skies during meteor showers. But I have been missing a trick. I recently learned that there are likely to be several meteorites sitting on the top of my London home.
Tiny meteorites, less than a millimetre wide, are probably perched on all our homes – and with a bit of effort you can get your hands on them. “Very few of us are going to find a big meteorite, but the fact that there are at least one or two tiny, shiny micrometeorites on the roof above my head right now, there’s something quite wonderful about that,” said Joshua Howgego, a meteorites expert who appeared at the public science festival, New Scientist Live, in London this month.
Meteorites are of great interest to scientists because they are almost-pristine remains from the creation of the solar system. In contrast to these space rocks, any rocky material on Earth has been destroyed and remade by geological processes countless times since our planet’s formation, 4.5 billion years ago.
In the early solar system, the planets formed from a disc of dust and gas orbiting the nascent Sun. The dust particles started colliding and sticking to each other until they eventually became large masses. Some of the rocks in that disc never made it into a full-size planet, and have been whirling around our solar system ever since, as comets, asteroids and – if they are less than a metre wide – meteoroids. When these crash into the Earth’s atmosphere, we call them meteors, and any bits that reach the surface we call meteorites.
“I think of meteorites as like time capsules from the early solar system,” said Howgego, who published a book this year called The Meteorite Hunters: On the Trail of Extraterrestrial Treasures and the Secrets Inside Them.
While it may be rare to see their fiery arrival, meteorites of varying sizes are constantly landing on Earth. Most of the time they go unnoticed and get mixed up with all the other rocks and dirt. Astronomers usually search for these space rocks in remote places, like Antarctica and deserts, where they stand out against the snow or sand. As well as their eyes, they may also use metal detectors, as most meteorites contain at least some iron and nickel, which are magnetic.
But smaller meteorites, too small to be easily spotted, could be anywhere. Flat roofs have long been a popular hunting ground for amateur astronomers and hobbyists, simply because any meteorites there won’t get mixed in with terrestrial rocks and soil. But this approach wasn’t taken seriously until a 2017 paper was published in the journal Geology.
This described a collection of 500 of the space rocks, discovered by Jon Larsen, a Norwegian photographer, who worked with three professional astronomers to analyse them. “This was a key paper proving he could find urban micrometeorites,” said Howgego.
How to Find Meteorites on Your Roof
The first step is to get up on a flat roof with bags and a dustpan and brush and collect as much of the dirt as you can, including any moss. People need to judge the roof’s safety and children should not do it unaccompanied.
Back down on the ground, this dirt should be washed by putting it in a bucket of water, and adding some liquid soap. Anything that floats or dissolves can be thrown away. Repeat this a couple of times until the water is clear. At the bottom of the bucket you should be left with tiny particles of rock – which may include some meteorites. Spread this out on a plate to dry.
Next you need a strong magnet – such as one used for “magnet fishing”, when people try to find metal objects in canals – and put it in a small plastic freezer bag. Pass this over the rock particles to find any specks that stick to the magnet through the bag and set them aside.
Lastly comes the hardest part. To identify the meteorites, you need to view the specks through a microscope, ideally one that has 50-fold powers of magnification. That’s higher than typical microscopes bought for home use, but second-hand ones aren’t too pricey.
Most of the grit on your roof will be jagged chunks showing its Earthly origins. Space rocks tend to be spherical – because they melt as they are heated by the atmosphere and then resolidify as spheres, often with distinctive patterns caused by the air molecules whipping past.
Not all magnetic particles will be meteorites, as round iron particles are also produced by car brakes, welding and coal plants. Picking out the meteorites from their appearance isn’t easy, until you are used to it. But guides are available, such as one by Jon Larsen called On the Trail of Stardust.
Key Insights from Micrometeorites
Rooftop meteorite hunting isn’t just a hobby. The growing amount of such space rocks being discovered and analysed is helping advance science. The collection in the 2017 paper brought new insights because, unlike most of the meteorites collected in Antarctica and so on, these ones must have arrived recently, as they were found in the gutters of a building that had been cleaned six years ago. Before then, Howgego said, “we didn’t really know what fresh micrometeorites looked like”.
Earlier this year, an amateur collector searching on mountains in Italy discovered an unusual meteorite that was an alloy of aluminium and copper. Its rare chemistry suggests it stems from a “protoplanet” that broke apart due to an impact while it was still forming, said Dr Matthew Genge, an astronomer at Imperial College London who worked with Larsen on the 2017 paper.
While Dr Genge still prefers to search in Antarctica, other astronomers have embraced the rooftop approach. Dr Matthias van Ginneken, a cosmochemist at the University of Kent recently began searching on top of Canterbury Cathedral – although his efforts were made harder by recent welding up there. His next plan is to search systematically on all the country’s cathedrals. “The bigger the catchment surface, you’re more likely to find micrometeorites,” he said.
But even those of us with a much smaller flat roof have a chance of interesting finds. Thousands of tonnes of meteorites rain down on the Earth all the time and it has been estimated that one tiny space rock falls per square metre per year.
“You are almost certainly sat under little pieces of dust from out of space that are older than planet Earth and are about the same age as the sun,” said Dr Genge. “They’re just sitting up above us all the time.”
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