In the early hours of February 6, 2017, more than 500 people across 12 provinces and one Canadian province reported sightings of a bright green fireball. The search began when weather radar data revealed an unmistakable meteor trail to Lake Michigan.

Researchers and local scientists, including teenagers from the Chicago area, were quickly mobilized, but failed to recover a large chunk of extraterrestrial visitors. But they didn’t come back empty-handed. This joint effort has resulted in the discovery of large quantities of micrometeorites.

The scientists presented these findings this week at the 85th Meteorological Society Annual Meeting in Glasgow, Scotland.

little messenger from outer space

Micrometeorites with diameters of about 0.01 to 2 mm are relatively common. Researchers estimate that about 60 tons of cosmic dust rains down on Earth’s surface every day. “This dust is everywhere,” said Arizona State University cosmochemist Maitrey Bose. The trick, of course, is finding it. Most of the dust on our planet is not extraterrestrial material, but various terrestrial dusts. (Antarctica and Greenland, both relatively pristine locations, are good places to look, but searches in urban settings also found micrometeorites.)

After the 2017 fireball event, the Aquarius Project, a community science initiative, gathered in the Chicago area to search for the culprit meteorite. The crowd now includes his members of the team associated with the Adler Planetarium, Shedd Aquarium, Field Museum of Natural History and NASA. Led by scientists and educators, a group of teenagers spearheaded the design and construction of an underwater sled that could be towed along the bottom of Lake Michigan. A coffee-table-sized sled called “Starfall” contained powerful magnets that picked up iron meteorites.

In 2018 and 2019, Aquarius Project team members enlisted the help of the University of Wisconsin-Milwaukee research vessel R/V. Nice Cay— to make Starfall work. While the ship was cruising Lake Michigan, the sled was lowered to about 60 meters below the surface and towed along the lake bed. Unsurprisingly, the sled’s magnets picked up all kinds of rusty metal debris, but also centimeter-scale objects that looked like meteorites.

Ultimately, most of the meteorite candidates were fragments of Earth’s rocks or slag, but the team thought it might be micrometeorites hidden in the scooped lake sediments. It was something.

Spectroscopy Reveals Secrets of Micrometeorites

Maria Valdes, a cosmochemist at the Robert A. Pritzker Center for Meteorite and Polar Research at the Field Museum in Chicago, and colleagues encased each micrometeorite candidate in epoxy resin and then hand-polished it to expose the interior. I was. The researchers then aimed a green laser at each candidate micrometeorite and measured different wavelengths of light scattered by the object. The technique, a type of spectroscopy, reveals chemical composition, she said Valdes. “Spectral patterns are the distinct chemical fingerprints of specific minerals,” she said.

The researchers found that five of the six micrometeorite candidates consisted of olivine or pyroxene. This is strong evidence that these objects are indeed micrometeorites, Valdes said. Interestingly, however, researchers found that the micrometeorites have different textures. The find says something about the origin of these objects, the researchers suggested. “They don’t all seem to come from the same parentage,” he said Valdes. The team concluded that while some of these micrometeorites may have been transported by his 2017 event, others probably were not.

In the future, Valdes and her team hope to analyze the isotopes of oxygen present in these micrometeorites. Such a survey would shed light on the types of solar system bodies that first dropped these cosmic dusts, Bose said.

Just in case that wasn’t enough to keep researchers busy, Valdez recently received an entirely new batch of candidate micrometeorites to study. she said.

—Katherine Cornay (@KatherineKornei), science writer

Quote: Kornei, K. (2022), Community scientists recover micrometeorites from Lake Michigan, Eos, 103, https://doi.org/10.1029/2022EO220382. Published August 15, 2022.

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