Clemson astrophysicists investigating meteorite thought to have struck home
PAWLEYS ISLAND, South Carolina — A team of Clemson University astrophysicists has visually confirmed that a small rock found in Melanie Casselman’s yard is a meteorite from outer space.
When Casselman found a peculiar rock on the side of her Pawleys Island yard on Sept. 26, she thought some neighborhood kids might have been throwing rocks at her house.
“I looked at my house and my windows, and everything looked fine, so I just walked right on by,” Casselman said. “I didn’t even pick it up.”
The mysterious rock slipped her mind until the next day, when her partner – Dennis Suszko – found another piece of rock near Casselman’s water spigot in the front yard.
Lying in a mulched flower bed, the smooth, speckled rock about the size of a golf ball stuck out like a sore thumb. Casselman and Suszko noticed, too, that it was much heavier than a normal gravel rock would be.
“When I saw the second rock, I said, ‘There’s one just like that on the side of the house; I just saw that yesterday!’ So we went over to the side of the house and Dennis immediately thought the same thing — somebody is throwing rocks at my house,” Casselman said. “These were odd-looking rocks, though. It wasn’t like anything around it, and I jokingly said, ‘We must’ve had a meteor shower last night.’”
The couple left home to run some errands, and while out, they used their cellphones to search for images of meteorites, still skeptical that a such a thing would fall — of all places — in Casselman’s yard.
When they returned home, they began to scout the yard for other chunks of matching rock.
“As we looked around for more pieces, we happened to look up and there was a chunk of shingles chipped out from the eave of the roof and a dent in the aluminum edging of the house. We’re not positive, but we believe that’s where the meteorite first struck before landing in the yard,” Casselman said. “Then, Dennis went to pick up his son, Christopher, from school and we said to him, ‘Look what we found. These might be rocks from a meteor shower.’ Christopher looked at both of them, and he said, ‘You do realize these two connect, right?’”
Christopher, 15, had put the two chunks of rock together like puzzle pieces.
“We had not even put two-and-two together — literally — but sure enough, the two pieces connect together. So, then, this was really something,” Casselman said.
To confirm whether the peculiar rocks were truly out-of-this-world, Casselman turned to Clemson University astrophysicist Sean Brittain.
“Melanie sent an email asking if there was anyone who could help her identify what this rock was,” said Brittain, a professor in the Clemson College of Science’s department of physics and astronomy. “At first, I was kind of skeptical, because we get people who will call in with, ‘I saw this bright light,’ or, ‘I have this rock in my backyard and I want to know what it is’ — we get a lot of those calls. Usually, it’s nothing you’d want to spend much time on. But with this one, Melanie had taken some really careful pictures of everything and I thought, ‘Okay, so this is legitimate.’”
Brittain looked at Casselman’s images — all 26 of them from varying angles — and became almost certain that the ball of iron and rock was a meteorite. To confirm, Brittain looped in physics and astronomy colleagues Brad Meyer and Máté Ádámkovics. At Clemson, Meyer researches the isotopic composition of meteorites while Ádámkovics has interest in the moons of Saturn.
The pair studied Casselman’s images with intrigue and they visually established that it is indeed a meteorite from outer space.
“The first and most important indicator was the dark, melted material on the outside of the rock,” Ádámkovics said. “It was clear that there were dark compounds with molten rock that showed flowlines — these dimples, almost like fingerprints. This meant that the rock was actually molten while it was moving through the air. The shape of the dark molten material on the outside of the rock was another indicator for us that it was a meteorite.”
The team then asked Casselman if the rock was attracted to a magnet. Casselman tested it out and sent video proof to Brittain that a magnet did grab the rock.
“After seeing this, it was clear that it has a very high iron content,” Brittain said. “Most rocks in your backyard, if you pick one up and stick a magnet to it, it’ll just fall off because it’s just silt and carbon. Melanie’s is mostly iron and it’s not rusty, so it hasn’t been sitting in the weather or anything. That tells us that it’s an iron-rich meteorite that landed recently.”
A meteorite of this size reaching the ground intact is quite common as opposed to a huge asteroid like the one believed to have led to the extinction of dinosaurs 66 million years ago. Asteroids of that scale strike the Earth only once every 100 million years or so. A meteorite like Casselman’s — weighing in at approximately 6.3 ounces — will survive its plunge through the atmosphere and reach the ground intact about 80 times a day.
“But one that hits a house or some kind of populated place, that’s a lot rarer,” Brittain said. “That’s what’s so unusual about this. It’s not so much that a meteor made it to the ground, it’s that it made it to the ground by hitting somebody’s house.”
Still, Brittain emphasized that a small-impact event like this one is a reminder of the importance of tracking near-Earth objects.
“The Tunguska Forest in Siberia was hit in 1908 by a 40-meter size object and it leveled 80 million trees over 830 square miles with an impact 1,000 times greater than the atomic bomb dropped on Hiroshima,” Brittain said. “Tunguska is a pretty remote place, so it wasn’t so great for the 80 million trees that were destroyed, but if something like that hit Greenville, it would be devastating. We’re really keen on tracking and watching objects of that size and larger because — although rare — when it happens, it’s mass catastrophe. ”
The Center for Near Earth Object Studies at NASA’s Jet Propulsion Laboratory leads the tracking mission by monitoring asteroids and other outer space objects with the goal of preventing catastrophic impact events from happening.
Casselman believes there is still a missing third piece of the meteorite and she intends to use a metal detector to try to find it.
“You can tell by its look that it must have broken into three pieces, but I haven’t been able to see that third piece with my eyes. So I borrowed a metal detector today and I’m going to see if I can’t just go across the entire yard to find it.”
Clemson University is working with Casselman and Suszko to arrange tests that will determine the meteorite’s age and composition, and also make deductions about its history and origin.
“In a lab, you could get the real mineral composition of the rock by looking at a sample of it under a microscope,” Ádámkovics said. “You could look at the crystallography of the mineral structure, or you could do atomic microscopy just to get the elemental composition, as well, to see how much iron or how much nickel there is. Meteorites with similar compositions are thought to have formed in similar locations in the solar system. So we can compare what we know about the composition of the rock and the composition of asteroids to get an understanding of where the rock would have formed or at what temperatures it was last melted at.”
Given the frequency of meteorites’ landing, it’s not likely that it holds much value, except to meteorite enthusiasts.
For the time being, Casselman is going to revel in the rarity of a backyard meteorite. And, eventually, patch the hole in her roof.