How the Structure of a Mammoth Meteorite Reveals the Rough and Tumble Nature of the Asteroid Belt

The Old Woman Meteorite is still revealing insights into outer space decades after its discovery

July 2, 2024

SIA2019-001834-S (1).jpg — *The Old Woman meteorite being prepared for cutting at the museum in 1979.* Smithsonian Institution

With more than 148 million specimens and objects, the vast majority of the National Museum of Natural History’s collections are off display. But each of these specimens — whether it be a moth, meteorite, moss or mammoth — tells a story that helps museum researchers make sense of the natural world. Each month, the Specimen Spotlight series will highlight a different specimen or object from the world’s largest natural history collection to shed light on why we collect.

In 1977, a giant meteorite took flight again. The mass of space rock, which weighed over 6,000 pounds, was wrapped in a cargo net and airlifted out of the Old Woman Mountains in southern California by a U.S. Marine Corps helicopter.

None — A U.S. Marine Corps helicopter arrives to airlift a meteorite out of the Mojave Desert east of Los Angeles. Smithsonian Institution

Named after the mountains where it was found, the Old Woman Meteorite weighed more than 6,000 pounds. For the next few years, the outsized meteorite was ensnared in a contentious ownership dispute (more information about the meteorite’s backstory is available here). Eventually, a 972-pound slice of the Old Woman meteorite found a home at the National Museum of Natural History. As part of the museum’s meteorite collection, it is among more than 45,000 individual specimens from 16,850 meteorites. These include slices, pieces, and chunks of meteorites found across the planet — and a few samples collected from an asteroid itself.

Museum technician Tim Rose was in charge of slicing a sample of the massive meteorite. It took him 50 days and 88 different wires using a wire saw to achieve a smooth, clean slice.

“I learned what worked best through experimentation,” said Rose, who now manages the museum’s analytical laboratories. “Being essentially solid metal, the meteorite cutting was very slow compared to any rock. With the wire changes, I could only get about four hours of actual cutting time per day.”

In addition to its monumental physical size, the Old Woman Meteorite also possesses a large amount of scientific intrigue. The slice revealed evidence of two different minerals inside the meteorite. The crystal patterns of these minerals, known as Widmanstätten patterns, reveal the meteorite’s initial composition and the rate that the original asteroid’s core cooled. The Widmanstätten pattern, which has a meshed appearance, has also been stamped by impact shocks which alter the original, clear crystal structure pattern. These impact shocks were caused by various collisions as the asteroid pinballed through outer space before it came crashing down through Earth’s atmosphere.

“Each meteorite can give us a bigger and better picture of what is happening in the Solar System over time.”

— Cari Corrigan, NMNH Research Geologist

“We know that this meteorite was once inside an asteroid, and we know something catastrophic had to happen to that asteroid to get that rock onto Earth,” said Cari Corrigan, a research geologist at the museum who specializes in studying meteorites. “We know it’s been impacted — the question is how many times did it get impacted and heated to mess everything up?”

Scientists have also examined the metal composition of the Old Woman Meteorite, finding that it is made up of mostly iron. Around six percent of the meteorite is composed of nickel, which helps researchers distinguish iron meteorites from Earth rocks. The nickel content of meteorites creates the internal patterning seen in many of these space rocks.

“At one point, this was a big blob of metal inside of an asteroid that was molten and then cooled,” Corrigan said. “To get that pattern, it has to cool at this really slow rate, so that all of those atoms of iron and nickel rearrange themselves into where they want to be forever, in their most stable configuration.”

Corrigan and her colleagues do not know exactly where the Old Woman Meteorite originated, but they are confident that it came from the asteroid belt between Mars and Jupiter, where most asteroids in the Solar System orbit. Scientists can track some meteorites back to their original spots, called Kirkwood gaps, in the belt if they have enough information on their path across our sky. But all meteorites still hold valuable information about the Solar System regardless of whether we know where exactly they came from.

“This rock can tell us a whole story about all the things that happened to it by looking at the minerals, shapes and the compositions and textures of the rock itself,” Corrigan said. “By teasing out the story of what happened to individual meteorites, each one can give us a bigger and better picture of what is happening in the Solar System over time.”

Emily Driehaus | | READ MORE

Emily Driehaus is a Science Writing Intern with the Smithsonian's National Museum of Natural History. She holds a master's degree in science journalism from New York University and has worked as a journalist and science writer covering everything from microbiology and climate change to particle physics and quantum computing. Her writing has been published in Sierra Magazine, Symmetry Magazine, VICE News, and other outlets. You can find more of her work here.