Students and a sled named Starfall are on the hunt for underwater meteorites, dropped as a bolide fragmented over Lake Michigan last year.
On January 16, 2018, a fiery green streak lit up Michigan's night sky, producing a fireball seen in seven states. As the meteorite moved through Earth's atmosphere, it exploded, flinging off debris until it splashed down in Lake Michigan. With many of its fragments hidden beneath the lake waters, locating the meteorite's fragments would be a challenge — one that a group of Chicago teenagers and a specially designed sled named "Starfall" rose to meet.
Almost immediately after the fireball's appearance, Christopher Bresky and his colleagues at Chicago's Adler Planetarium began strategizing the best way to involve kids in recovering the fragments. The museum has engaged youth in a myriad of astronomical projects in the past, from monitoring light pollution in their neighborhoods to using balloons to study the 2017 total solar eclipse. This time, they’re hunting for underwater meteorites, collaborating with local students, the Shedd Aquarium, and the Field Museum as part of the Aquarius Project.
"It's all about exploring unexplored spaces, and the discoveries that come with it," says Laura Trouille (Adler Planetarium). Trouille presented the ongoing outreach program at the January meeting of the American Astronomical Society in Seattle, Washington.
Handful of Needles in a Hayfield
The first task was to figure out where the meteorite fragments had landed. Adler sits on the shore of Lake Michigan, so the splash zone was literally in their backyard. Although some fragments had hit land, the prospect of having teens design a robot to dive for meteorites under water was too enticing to pass up. At the time, no systematic underwater meteorite hunts were known, though later that year researchers would recover fragments from the Pacific coast.
Led by Bresky, members of the burgeoning Aquarius Project reached out to Marc Fries, a meteorite scientist at NASA's Johnson Space Center in Houston, Texas. Fries had heard about the meteorite via social media only a few hours after its splashdown and had calculated the strewn field, the footprint where debris could be found. The precise tracking by weather satellites allowed him to estimate a five-mile map of potential meteorites.
The looming question on everyone's mind was how to find the pieces beneath hundreds of feet of water. Only a handful of meteorites have been recovered underwater, but Fries said they were all much larger than what Project Aquarius hoped to find. "All were large stones, all were seen landing in the water, and someone dived in after them soon thereafter," Fries says.
The fragments from the 2018 meteorite were much smaller; Trouille estimates that most would be at most the size of a quarter. Yet these tiny pieces can still provide insights about the parent asteroid, Fries says. According to Trouille, when the teenagers asked Fries during a teleconference how they would manage to retrieve the fragments, he said, "I don't know. We're going to find out together."
To locate the hidden treasure, the Aquarius team designed a magnetic sled, Starfall, that could be dragged behind a boat. Built from off-the-shelf parts, the sled holds what Trouille describes as a “beater,” similar to a kitchen mixer, protruding off the back to stir up the lake's sediment and uncover any space debris. A camera helped to scan the unmapped lake floor. Most importantly, the sled carries powerful magnets to capture the metallic meteorite fragments.
Over the course of the year, Bresky says that more than 100 students have helped to design and execute the collection process over the course of weeks or months. Several of them spent the summer onboard a boat, lowering Starfall into the chilly Lake Michigan waters for multiple half-mile runs. The hunt was on.
Almost from the moment it hit the water, Starfall was making waves. When the sled's camera took its first peek at the bottom of Lake Michigan, it discovered a host of invasive mussels in a region previously thought to be too oxygen-poor to support them. Starfall revealed that the mollusks had spread more thoroughly than anticipated. "As far as the eye could see, there was mussels," Trouille says.
Meanwhile, the sled hauled in roughly 20 pounds of sediment from the lakebed last summer. Team members are now in the process of sorting through the trove. Project Aquarius plans to return to the water later this year to continue the hunt.
Teens Teaching Teens
Collecting potential meteorite samples was only the beginning. Sorting through it to find meteorites takes far more time and involves teenagers, cosmochemists, geologists, and astronomers — and the local library.
"There is quite a bit of content, so we are asking teens across Chicago at public libraries to help us as community scientists in this endeavor over the next few months," Bresky says.
A core group of students are teaching their peers how to sort through the fragments to pull out organic material and human-made objects that are definitely not meteorites. "There is such a large amount of content, the more eyes the better," Bresky says.
The remaining fragments are then sent to Chicago's Field Museum, where they can be analyzed with instruments that can't be hauled to the library. An electron-scanning microscope helps resolve small-scale structure, while a Raman spectroscope helps identify molecular and crystal structures. Some pieces may be tossed into acid to see if they carry any of the acid-resistant particles which may be present in meteorites.
So far, Bresky says Aquarius has found "a few 'hard maybes,' but not one 'hard yes' yet." However, he remains optimistic. "Science being a journey, we are all continually excited by each part of this ride."
Whether or not the Aquarius Project finds any meteorites, Fries says the involvement of so many students is its biggest success. He describes meteors and meteorites as a "very personal aspect of planetary science." While most people have seen a shooting star, and may have touched a meteorite, the Aquarius Project takes students beyond even that.
"Not only is this meteor something that happened in the students’ own neighborhood, it is a mystery and a challenge that they get to participate in directly," Fries says. "It is a learning experience that will stay with them for the rest of their lives."