Astronomical research of a special kind: With the help of a citizen scientist, researchers have tracked down two micrometeorites in the dust of a house roof. By analyzing the tiny objects and using computer simulations, the team was then able to determine their origin in the solar system. One of them comes from the region close to Earth, while the other could even have come to us from the distant Kuiper Belt. The new method could help to gain new insights into the history of the solar system using micrometeorites in the future, say the researchers.
They are constantly falling unnoticed onto our planet: so-called micrometeorites are mostly particles of cosmic dust, which, unlike their larger relatives, are typically only a few hundred micrometers in size. Due to their low weight, they are slowed down considerably when they enter the Earth’s atmosphere, meaning they do not burn up completely and cannot reach the Earth’s surface. The Earth thus captures around 100 tons of these grains from space every day.
“Micrometeorites are much more common than larger meteorites, so we could generate much more data from them and learn a lot about our solar system. They can come from very different areas,” says co-author Beate Patzer from the Technical University of Berlin (TU Berlin). “However, it is still a major challenge for science to find out where the micrometeorites found on Earth were formed,” says the astrophysicist.
Citizen scientist detects micrometeorites
The study began with the search for micrometeorites. The team did not have to go to remote locations, but rather to the roof of the physics building at TU Berlin. As is now known, micrometeorites also fall on roofs. The team therefore simply swept up the deposits on the physics building roof and collected them for their search. “The material was then suspended in water to get rid of small leaves and the like. We then heated the sediment to 600 degrees to destroy microbes and other organic material. The material is then sieved and the search for the micrometeorites begins,” says lead author Jenny Feige from TU Berlin.
As the team reports, it is not only astrophysicists who are enthusiastic about the tiny cosmic creatures and track them down in this way: a global community of citizen scientists has developed who collect micrometeorites on their roofs and identify them using light microscopy. Some of them are thus given special expert status – such as amateur micrometeorite researcher Scott Peterson from Minneapolis. “That’s why we asked him to take a look at our samples, because he simply has the best eye for identifying micrometeorites under the microscope,” says Feige.
Among the numerous tiny particles, which come from welding work, fireworks or abrasion in road traffic, Peterson actually discovered two micrometeorites. They could be recognized by characteristic features that arise when the cosmic dust particles are heated and melted as they fly through the Earth’s atmosphere. After they have lost a large part of their mass, the rest crystallizes and forms different structures depending on the type of environmental conditions. One of the two micrometeorites has a structure reminiscent of a turtle shell. In the other specimen, however, certain metals had apparently separated from the rest during melting and then solidified into a spherical partial structure when it cooled. “Based on this nose, we can conclude that this micrometeorite entered the atmosphere with the sphere first,” says Feige.
On the trail of the origin
The team then turned its attention to the challenge of getting to the bottom of the origin of the two micrometeorites. The results of analyses of the material can provide clues. “Using the ratio of different isotopes with different half-lives and a physical model that describes the formation of these isotopes, we can determine the flight time of the extraterrestrial dust particles to Earth – and thus their place of origin in the solar system,” explains Patzer. Feige continues: “For this type of analysis, however, we have now created a complex computer simulation for the first time, which takes into account possible orbits of the interplanetary dust particles, the size of the dust grains, their composition and density, radiation profiles of the sun and cosmic radiation from interstellar space, evaporation rates during entry into the Earth’s atmosphere and a large number of other parameters.”
The most important clues from the material can be provided by the radioactive isotopes aluminum-26 and berylllium-10, the researchers explain. These substances were identified in the two micrometeorites and other specimens from other locations using a special form of mass spectrometry. The results could then be compared with the information from the computer simulation, which predicts the enrichment of these radioisotopes in the micrometeorites depending on the flight time and thus the place of origin in space.
A “turtle” from the outer solar system
As the team reports, they were able to assign a place of origin in the solar system to the two finds from the roof and four other micrometeorites with a high degree of probability. The micrometeorite with the turtle-like appearance therefore comes from the outer solar system. It could have formed from comets in the area of Jupiter or from rock material in the Kuiper Belt. The micrometeorite with the “nose”, on the other hand, comes from the inner solar system up to the asteroid belt between Mars and Jupiter, say the researchers.
They now see considerable potential for research in their approach: “With the result, we were able to demonstrate the basic suitability of our method,” says Feige. This means that an interesting possibility of gaining astronomical insights using micrometeorites is emerging. Finally, the researcher highlights the important aspect of the location of the find: “Finds on our house roofs are particularly valuable because here we know very precisely how long the micrometeorites have been on Earth: it cannot be older than the roof itself. In the case of finds from the deep sea or the Antarctic, on the other hand, the micrometeorites could have been there for millions of years, which makes the results less certain,” says Feige.
Source: Technical University of Berlin, specialist article:
Philosophical Transactions of the Royal Society B, doi: 10.1098/rsta.2023.0197