On the roof of Canterbury Cathedral, two planetary scientists search for cosmic dust. While the red brick parapet hides the streets, buildings and trees far below, only wispy clouds block the deep blue sky that stretches into space.
The roar of a vacuum cleaner breaks the silence and researcher Dr. Penny Wozniakiewicz, dressed in a hazmat suit with a large vacuum cleaner backpack, carefully traces a gutter with the vacuum machine’s tube.
“We are looking for small microscopic spheres,” explains her colleague Dr. Matthias van Ginneken from the University of Kent, also dressed in protective clothing. “Right now we’re collecting thousands and thousands of dust particles, and we’re hoping that a minuscule number will come from space.”
Most of the alien dust that bombards Earth each year evaporates into the atmosphere – some models suggest 15,000 tons reaches Earth’s atmosphere (the equivalent of about 75 blue whales). But according to one estimate from Antarctica, about 5,200 tons of micrometeorites fall to Earth. These particles, which most likely come from comets and asteroids, are small, between 50 microns and two millimeters in diameter.
“You have to be a bit of a detective,” says Van Ginneken. The extreme heating upon entering the atmosphere changes many of the minerals and “you have to figure out the nature of the original particle based on the limited information you have.”
Researchers turn to micrometeorites for clues about the chemistry of asteroids and meteorites. By looking at chemical variants known as isotopes, scientists can gain more insight into the parent body where the cosmic dust came from – and what happened to it as it entered Earth’s atmosphere.
In addition, there was more cosmic dust present in the past because there were many more collisions between objects in the solar system when Earth was young. That dust is trapped in rocks and could point to what happened in Earth’s history in our planetary environment, and how it has changed.
Van Ginneken and Wozniakiewicz are trying to understand how the flow of micrometeorites changes, among other scientific questions.
“If you can understand the amount of dust particles arriving over the surface, you can make estimates of the amount of material arriving at Earth over time, and therefore potentially what contribution space dust makes to Earth. chemistry on Earth,” says Wozniakiewicz.
“And that’s in two ways – some of [the cosmic materials] survive on the surface and can participate in surface chemistry. Some of them burn up in the atmosphere and can participate in atmospheric chemistry.”
Micrometeorites can seed elements on land and seas that are not common on Earth’s surface, as well as in the atmosphere – which could affect how these systems behave.
Wozniakiewicz and Van Ginneken are looking for a specific type of extraterrestrial dust: cosmic spheres. These small spheres are relatively easy to identify compared to other dust because of their distinctive shape, but it takes a microscope to be sure that a cosmic spherol did not come from Earth. This makes them useful in estimating how much cosmic dust has fallen in a given place over a given period of time.
It was thought impossible to collect cosmic dust in the urban environment; it was confined to pristine places, such as Antarctica, or in fossilized sediment. But in 2009, Norwegian jazz musician turned cosmic dust hunter Jon Larsen began combing through hundreds of pounds of urban dust particles in search of cosmic dust. In 2017, Larsen and colleagues, including Van Ginneken, published a groundbreaking article in the journal Geologywhich shows that anyone with a microscope and patience can discover cosmic spheres.
Micrometeorites tell you about millions of objects… They tell you about the asteroid population as a whole
Dr. Penny Wozniakiewicz
But it is difficult to collect micrometeorites for scientific research, even though they continually fall onto the Earth’s surface. The particles are easily contaminated, which could compromise their use in research. (But that’s not why Van Ginneken and Wozniakiewicz look like aliens dressed in white — they’re protecting themselves from bird flu, possibly contained in the feces and bird bones we see on the roof.)
Larsen “started the whole era of urban micrometeorites,” says Van Ginneken. “Since then, more and more people have been doing this as a hobby. Part of what Penny and I want to do is get science involved.”
Cathedral roofs, like those of Canterbury, are ideal for cosmic dust hunting because they are large, inaccessible and largely untouched. We enter through a mostly barred wooden door, at the back of the cathedral’s main Trinity Chapel, up hundreds of tightly winding steps, and then through another specially unlocked door to reach one of the cathedral’s roofs. This was Van Ginneken and Wozniakiewicz’s last roof of the day; they had gone to several other roofs of the cathedral. They have also gathered dust from Rochester Cathedral and hope to add Salisbury and Winchester to their list.
Van Ginneken would like to sample many roofs to understand the biases that creep into urban micrometeorite collections, such as the effect of rainwater. The advantage of roofs is that they are easily accessible, he says. Going to Antarctica, where a lot of micrometeorite research has been done, “is very expensive, requires a lot of preparation and there is a limit to the amount of samples you can take with you.” Moreover, the study is limited to a specific climate and latitude. Roofs increase the possibilities to investigate how these small dust particles interact in different environments.
The abundance of urban micrometeorites also opens up planetary science to those who don’t necessarily have access to the spoils of larger space missions. And there is increasing interest in the riches of space. For example, NASA’s OSIRIS-REx mission last year returned material to Earth from the asteroid Bennu, which is more than 4.5 billion years old.
“Those missions are great,” says Wozniakiewicz. “They go to one object, and they tell you a lot about that one object. Micrometeorites tell you about thousands, millions of objects… They tell you about the asteroid population as a whole, a snapshot of all the different processes, all the different bodies out there. And then you can compare those samples, along with meteorites, to the samples brought back from these missions.”
Cosmic dust could also hold clues to our own planet in the distant past, says Dr Martin Suttle, lecturer in planetary sciences at the Open University. It could also have created a hospitable environment on early Earth for life to arise spontaneously, according to a new paper published by Suttle and colleagues in Nature Astronomy.
“More dust came to Earth, perhaps a thousand times more dust, than today,” he says. “That dust contains many substances that are attractive as raw materials for early prebiotic chemistry, such as iron metal, which is otherwise not present on the Earth’s surface.”
But collecting the cosmic dust is just the beginning of the research process, and perhaps the easier part – despite all the cathedral steps. The dust bags are now sterilized so they can be handled safely, and then the scientists examine each particle under a sterile microscope.
“We will spend hours and hours and hours and hours extracting spheres and hoping it is a cosmic sphere,” says Van Ginneken.