About 25,000 years ago, a meteor traveling at about 27,000 miles per hour crashed into the Earth just southwest of what is now Odessa, Texas.
The meteor, about 10 meters in diameter, screamed in at a low angle. Part of it drove into the limestone, digging a crater. Some of it scattered around the site and the rest bounced off the Earth’s surface and shot back into space.
When the dust and rock settled, the meteorite had created a crater about 175 yards wide—almost the length of two football fields—and 33 yards deep.
The Odessa Crater is not the biggest impact crater, but it might be one of the most unusual. Research scientist David Littlefield estimates that there was just a 1 percent chance of a meteor striking the Earth at such a shallow angle.
“Odessa was a unique impact, almost a ricochet whereas that’s not the usual impact,” he said. “We’re fairly certain it was a grazing (impact).”
That scenario overturns a previous conclusion that the meteor was about two meters in diameter and struck a much more direct hit on the site.
The new finding is the result of an unlikely collaboration of researchers and the calculating muscle of a supercomputer.
An observer calls the crater, which is little more than a rocky depression, a “rather uninspiring” sight, but it has remained a source of scientific inquiry.
The research not only changed the thinking on what happened in that ancient event, but it has helped validate computer code used on complicated modern problems of high-speed impact.
The crater’s history
Today, the crater’s not much to look at. It’s been filled in over time and the rocky soil is dotted with scrub oak and weeds. A rock rim protruding above ground is the only evidence of a crater.
No one realized a meteorite created the crater until 1922. No research was done until the late 1930s when geologists came poking around, hoping to find remains of the meteorite.
Glen Evans, a geologist and naturalist, began drilling at the site in 1939, under the direction of E.H. Sellards, who was director of the Texas Memorial Museum and the Bureau of Economic Geology (BEG). The project found bits of nickel and iron here and there, but nothing sizable.
Skip ahead to 2000. Evans and Charles Mear, a BEG geologist, wrote a paper about the crater, which was published by Baylor University’s Strecker Museum.
They didn’t publish a conclusion on the meteor’s size and angle of impact, but others have speculated that it was about two meters in diameter and hit the site straight on.
NASA’s Deep Impact
The problem with studying craters is that no one really gets a chance to see them being created.
Until July 4, that is. That’s when NASA’s Deep Impact mission crashed an 820-pound spacecraft into the Tempel 1 comet 83 million miles from Earth.
The mission could address the question research scientist David Littlefield and his students at The University of Texas at Austin are trying to answer through a simulation: What happens when a metal object strikes a geological formation like a planet or comet?
Littlefield and Anthony Dawson, a mechanical engineering student, are getting information from NASA about the crash and using it to compare their simulations to what happened.
That will take some time because NASA scientists are still collecting data from the collision.
Most of the factors are known: Unlike the Odessa crater, they know the size, composition and speed of the probe as well as its impact trajectory.
What’s still up in the air, Littlefield said, is the composition of the comet.
“Until all the data are available we don’t have anything to compare it to,” Littlefield said. “If the crater is unlike the one that we have simulated then the obvious thing to point to is the composition of the comet.”
So far, the simulations he and Dawson have made are in line with those made by NASA scientists, Littlefield said.
Running the NASA data also will help show that the tools used to simulate the creation of craters is correct.
Littlefield and Dawson weren’t involved until Dawson called NASA to see if it was doing simulations. It wasn’t, but agreed to share data.
Photos: NASA/JPL-Caltech/UMD, from NASA’s Deep Impact Web site.
Over at the Texas Memorial Museum, Dr. Ann Molineux, collections manager of the Non-vertebrate Paleontology Laboratory, was putting together an exhibit and multimedia CD on the Odessa Crater. What’s multimedia without video, especially when the video can show a meteorite crashing into Texas?
That’s when she contacted Littlefield, a research scientist in the Institute for Computational Engineering and Sciences. She asked him to put together a 3-D movie of the impact. He uses visual simulation to show results of his research into high-speed impacts.
Littlefield moved to the University of Alabama-Birmingham as a professor of mechanical engineering. He continues to work with students in Austin.
“We told them that we could help them with that,” Littlefield said, “but then we decided to carry it to the next level so it would be something that we’d consider useful to us as well.”
Littlefield’s regular research is in what happens when fast-moving objects strike other objects, which is the kind of thing that interests the Army and Navy. They fund some of his research to find out how underwater blasts affect structures and what happens when high-speed missiles strike armor.
The Odessa project presented the opportunity to validate the computer code with a different set of conditions.
The researchers read the Evans-Mear paper and talked to both men about the crater and the data they collected. “We had a lot of characterization data we could use,” Littlefield said.
Littlefield and graduate student Paul Bauman plugged in the geologic data collected in the 1940s and began running simulations on the 224-processor IBM Power 4 cluster called Longhorn at the Texas Advanced Computing Center.
“They were very large calculations,” Littlefield said. “We typically run these on between 32-64 processors and they run for seven to eight days.”
They concluded that the meteorite was much bigger, the velocity much faster and the angle much shallower than previously thought.
At 10 meters in diameter, the meteor would have been about half the height of a balloon character in the Macy’s Thanksgiving Day Parade. But instead of helium, it was made of nickel and iron. And, at 27,000 miles per hour, it moved about 10,000 miles faster than the space shuttle instead of loping along at parade speed.
Littlefield said it’s likely some of the meteor bounced back into space.
“It’s not unreasonable for that to happen, to produce a grazing impact and for it to escape,” he said.
“When you think about it what are the chances of a meteorite just skimming the planet and bouncing off? That’s a very low probability event.”
A sign shows today’s visitors to the Odessa Crater what geologists found when, in the 1940s, they drilled 165 feet below the surface, hoping to find remains of the meteorite.
For Ann Molineux of the Texas Memorial Museum, the project illustrates the way new technology can breathe new life into old information.
“It’s a wonderful example of why you keep old collections or old data,” said Ann Molineux of the Texas Memorial Museum. “The way new technology can be applied to old data and give you entirely new insights and new research results that may contradict or expand upon earlier research.”
Littlefield and Bauman aren’t done with the crater, although they’ve scaled back their time on the project. They are now looking at the shape of the meteorite.
“What people normally assume is that meteorites are round, spheres,” he said. “We know that’s not true. All you have to do is look at the images that were captured from the Eros (asteroid). That thing looked like a potato. It’s fairly reasonable to assume that whatever impacted Odessa wasn’t a sphere either, it was something else.”
Littlefield said he learned a lot about geology during the project. “We were neophytes,” he said. But, by reading the papers and talking to Mear and Evans, he and Bauman developed a base of geologic information.
But such education goes both ways.
“They learned a lot about impact, too,” he said.
BY Tim Green
PHOTOS at Odessa crater site: Texas Memorial Museum
PHOTO on banner graphic: E.H. Sellards inspects weathered, steeply sloping
upper-Fredericksburg limestone exposed by trenching on the southeast side of the main crater.