Meteor Fragment From Wisconsin Fireball Discovered by Farmer
By Tariq Malik
SPACE.com Managing Editor
posted: 17 April 2010
05:23 am ET
A small chunk of rock believed to be a fragment from a meteor that burst into a stunning fireball over Wisconsin Wednesday night was discovered by a farmer after it fell on the roof of his shed.
The meteor fragment is peppered with gray, white and reddish minerals, though one side is covered in what scientists called a “fusion crust” – a layer of dark material forged during the meteor’s fiery passage into Earth’s atmosphere. It weighs just 0.2 ounces (7.5 grams) and is about 2 inches (5 cm) long and less than an inch wide.
A camera mounted to a campus building at the University of Wisconsin-Madison caught the Wisconsin meteor’s explosive demise. The meteor’s sonic boom and explosion were also seen and heard by numerous witnesses, and sparked frantic 911 emergency calls across six different states, according to the Near-Earth Object Office at NASA’s Jet Propulsion Laboratory (JPL) in Pasadena, Calif.
When the meteor exploded, it unleashed as much energy as the detonation of 20 tons of TNT, NASA scientists said. Their analysis found that the parent meteor was about 3.3 feet (1 meter) wide before it blew apart.
The first reported piece of the space rock was discovered by a Wisconsin farmer Thursday morning and brought to the University of Wisconsin-Madison for analysis.
The space rock was not associated with the Gamma Virginids meteor shower, which was under way at the time. Instead, it most likely came from the asteroid belt, NASA scientists said.
Scientists at the geosciences department of the University of Wisconsin-Madison studied the meteor fragment briefly using a scanning electron microscope and an X-ray spectrometer. The rock includes traces of magnesium, iron and silica compounds, as well as other common minerals like olivine and pyroxene.
The meteor fragment also contained iron-nickel metal and iron sulfide, minerals typically found in primitive meteorites discovered on Earth, but scientists hope to see more pieces of the exploded meteor for comparison.
“Until we look at more samples and are able to take some measurements, we won’t know what kind of meteorite it is,” said Norika Kita, a meteorite expert at the university who studied the meteor fragment with colleague Takayuki Ushikubo.
Researchers are convinced more fragments exist based on the first sample’s “fusion crust,” which is only on one side of the rock.
“If the meteorite had broken up high in the atmosphere it would have developed a fusion crust that completely covered the exterior,” explained geosciences professor John Valley also of the University of Wisconsin-Madison. “This doesn’t have that, so it broke up low enough that I’d have to say more of it hit the ground.”
The discovery of meteor fragments and meteorites known to have entered Earth’s atmosphere over Wisconsin is exceedingly rare, university officials said.
Only a dozen meteorites have been documented in Wisconsin, with shards from seven of them recovered and on display at the University of Wisconsin-Madison’s Geology Museum.
Most of those are more than 50 years old.
Objects as big as washing machines typically fall into Earth’s atmosphere on a monthly basis, but most burn up before reaching the ground. Many of the resulting fireballs are not seen because they occur over remote areas or over the ocean. Earth is more than two-thirds ocean.
“The frequency of space debris entering our atmosphere that is large enough to generate a fireball is something on the order of once or twice a day,” said Don Yeomans, manager of the Near-Earth Object Office at JPL. “What is somewhat unique about this one is that it was witnessed by so many and captured on tape. Sounds like it was spectacular. I wish I had been there to see it, too.”
University of Wisconsin-Madison officials are asking anyone finding pieces of the meteorite to bring them to the UW-Madison Geology Museum at 1215 W. Dayton St. in Madison.
Meanwhile, avid skywatchers have a chance to see meteors again in the night sky. The Lyrid meteor shower should be visible to observers on clear nights between April 16 and April 22.
Anywhere from 10 to 20 meteors an hour could be seen, according SPACE.com skywatching columnist Joe Rao.