by On the roof of Canterbury Cathedral, two planetary scientists are searching for cosmic dust. Although the red brick parapet hides the streets, buildings and trees far below, only wispy clouds block the deep blue sky that stretches into outer space.
The roar of the vacuum cleaner breaks the silence and researcher Dr. Penny Wozniakiewicz, dressed in a hazmat suit with a bulky vacuum backpack, carefully traces a drain with the tube of the suction machine.
“We are looking for small microscopic areas,” explains her colleague, Dr Matthias van Ginneken from the University of Kent, who is also clad in protective gear. “Right now, we’re collecting thousands and thousands of dust particles, and hopefully a minuscule number that came from space.”
Most of the extraterrestrial dust that bombards the Earth evaporates in the atmosphere every year – some models suggest that 15,000 tonnes reach the Earth’s atmosphere (the equivalent of about 75 blue whales). But about 5,200 tons of micrometers fall to Earth, based on an estimate from Antarctica. These particles, which probably come from comets and asteroids, are tiny, between 50 microns and two millimeters in diameter.
“You have to be a detective,” says Van Ginneken. The intense heat 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 are turning to micrometeorites for clues about the chemistry of asteroids and meteorites. By looking at chemical variants known as isotopes, scientists can understand more about the parent body that cosmic dust came from – and what happened to it as it entered Earth’s atmosphere.
Also, in the past, cosmic dust was more abundant, because there were many more collisions between objects in the solar system when the Earth was young. That dust is trapped in rocks, and it can tell what has been happening in our planetary neighborhood through Earth’s history, and how it has changed.
Van Ginneken and Wozniakiewicz are trying to understand how the flux of micrometers changes, among other scientific questions.
“If you can understand how many dust particles are coming across the surface, you can make some estimates of how much material is coming to Earth over time, and so, perhaps, what contribution of space dust to chemistry on Earth,” says Wozniakiewicz.
“And that’s in two ways – part of it [the cosmic materials] live on the surface, and can participate in the surface chemistry. Some of them burn up in the atmosphere, and they can participate in the chemistry of the atmosphere.”
Micrometeorites can deposit elements on the land and seas that are not common on the Earth’s surface, and in the atmosphere – which can influence the behavior of these systems.
Wozniakiewicz and Van Ginneken are looking for a specific type of extraterrestrial dust: cosmic spherules. These tiny spheres are relatively easy to identify compared to other dust, due to their characteristic shape, but a microscope is needed to be sure that a cosmic spherule did not come from Earth. This makes them useful for estimating the amount of cosmic dust that has fallen in a given place over a given period of time.
Collecting cosmic dust in the urban environment was thought to be impossible – it was limited to pristine places, such as Antarctica, or in fossil sediments. But in 2009, Norwegian jazz musician turned cosmic dust hunter Jon Larsen began combing hundreds of kilograms of urban dust particles, searching for cosmic dust. In 2017, Larsen and his colleagues, including Van Ginneken, published a seminal paper in the journal Geologyshowing that anyone with a microscope and patience could find cosmic spheres.
Micrometeorites tell you about millions of objects… They tell you more about the entire population of asteroids
Dr Penny Wozniakiewicz
But it is difficult to collect micrometeorites for scientific study, even though they fall continuously on the Earth’s surface. The particles are easily contaminated, which could jeopardize their use in research. (But that’s not why Van Ginneken and Wozniakiewicz look like aliens in white coats – they’re protecting themselves from bird flu, perhaps in the bird droppings and bones we see on the roof.)
Larsen “started the whole era of urban micrometeorites”, says Van Ginneken. “Since then, more and more people are doing this as a hobby. Part of what Penny and I want to do is bring science into it.”
Cathedral roofs, like Canterbury houses, are ideal for cosmic dust hunting, as they are large, inaccessible and mostly untouched. We enter through a usually barred wooden door, at the back of the main Trinity chapel in the cathedral, up hundreds of tightly wound steps, and then through another door that is not specially locked to reach one of the cathedral’s roofs. This was the last roof of the day for Van Ginneken and Wozniakiewicz – they had walked up to many other roofs on the cathedral. They have also collected dust from Rochester Cathedral, and hope to add Salisbury and Winchester to their list.
Van Ginneken wants to sample many roofs, to understand the biases that go into urban micrometeorite collections, such as the effect of rainwater. The advantage of roofs is that they are easily accessible, he says. It is very expensive to go to Antarctica, where a lot of research has been done on micrometerite, a lot of preparation is required, and there is a limit to the amount of samples you can bring back”. Also, the research is limited to a specific climate and latitude. Roofs expand the opportunities to investigate how these tiny dust particles interact in different environments.
The abundance of urban micrometeorites makes planetary science available to those who don’t necessarily have access to the transport from larger space missions. And interest in the bounties of outer space is growing. NASA’s OSIRIS-REx mission, for example, returned material to Earth from the asteroid Bennu, which is more than 4.5bn years old.
“Those missions are amazing,” says Wozniakiewicz. “They go to one thing, and they tell you a lot about that one thing. Micrometeorites tell you about thousands, millions of objects… They tell you more about the population of asteroids as a whole, insight into all the different processes, the different bodies that are out there. And then you can compare those samples, as well as meteorites, to the samples that are being brought back from these missions.”
Cosmic dust could hold clues to our own planet’s distant past, says Dr Martin Suttle, a lecturer in planetary science at the Open University. It may also have created a hospitable environment on early Earth that allowed life to spark spontaneously, according to a new paper published by Suttle and colleagues in. Natural Astronomy.
“There was more dust coming to Earth, maybe 1,000 times more dust, than there is today,” he says. “That dust includes a lot of things that are attractive as raw materials for early prebiotic chemistry, things like iron metal, which are otherwise not on the surface of the Earth.”
But collecting the cosmic dust is only the beginning of the research process, and arguably the easiest part – despite all the cathedral stairs. The dust bags will now be sterilized so they are safe to work with, and then the scientists will examine each particle under a sterile microscope.
“We spend hours and hours and hours and hours just removing spheres and hoping that one is a cosmic spherule,” says Van Ginneken.
