U. South Florida Graduate Student Confirms Asteroid Site in Panama
18 Jun 2001
(Source: University of South Florida)
University of South Florida
Marsha Strickhouser, (813) 974-4014
Livio Tornabene, (813) 598-4231
TAMPA, Fla. - In August 1998, Bob Stewart, a retired geologist from the Republic de Panama, showed up on the doorstep of USF's Department of Geology bearing a heavy knapsack of rocks. Not just any rocks, but unusual rocks he recovered near the Panama Canal Zone in the middle of what he believed to be a possible asteroid impact site. They were not at all consistent with the local geological setting. They showed indications of shattering, melting and flow features that were forever frozen in time and marking a catastrophic event in the Earth's geologic past.
When seven of those rocks fell in to the lap of Jeffrey Ryan, USF's interim chairman of the geology department, he immediately handed them over to a young master's student eager to work on anything dealing with planetary science, Livio L. Tornabene.
Until then, the site had not been seriously investigated as a possible impact site since it had been first discovered in August 1972. Stewart had noticed the anomalous circular structure during a survey and mapping project in the Panama Canal Zone. He collected samples in 1990 and 1995. But until summer 1998, the samples sat undisturbed in his garage.
Tornabene had Stewart's notes and the seven rocks, but knew that any proof, if it were indeed an impact site, would probably be microscopic. "At larger diameters, there's pretty much nothing left of the impacting body," he said. "The asteroid vaporizes and melts upon impact. You could literally have a giant gaping hole in the earth, but unless you prove it with certain microscopic features caused by intense shock (like shocked quartz or diamond formation), you have nothing."
Tornabene, co-investigator Tom Carey and a local guide set out with maps and canteens through the rain forest during the heat and humidity of July. "It was the worst time of year we could possibly go, considering it was summer and still deep into the rainy season," he said.
The trip was an hour and 40 minutes total out of Panama City, about an hour to the Gamboa Docks and then west on the Panama Canal about six and a half miles on a 15-foot dingy. They spent 12 hours a day for two weeks searching and collecting samples. "This structure in the Panama Canal Zone was eroded and flooded on the northwest side, a lot more subtle than the one in Arizona, which is well persevered in the dry desert climate.
It was covered by dense forest, and battered by the tropical environment, which accelerates erosion. It was very difficult to view a structure and to find rocks," he said.
He obtained about 30 samples that weighed about 200 pounds. This time he found more anomalous rocks bearing all different colors -- light blue, green, white, beige and black.
"Since the proof is usually microscopic, you just have to go to the site, sample it and look at the structure in great detail," said Tornabene, who now calls the site the Gatun Structure because it's located near the Gatun Lake.
In May, Tornabene found the proof he was looking for in the form of diaplectic glass, which is a purely impact-generated phenomenon. Tornabene presented the discovery at the spring meeting of the American Geophysical Union in Boston.
Tornabene estimates the actual asteroid was roughly 150 meters in diameter - larger than one-and-a-half football fields - and traveled at a minimum of 25,000 miles per hour - about the top speed of the space shuttle. This site is roughly 2.2 to 3 kilometers or two miles in diameter - more than twice the size of the one in Arizona most people are familiar with. Only 177 known impact structures like it have been identified to date.
"When you look at the moon, you see millions of craters, especially smaller ones," Tornabene said. "We've been hit probably 20 times more than the moon. And yet, we don't see as many at the surface. It's the active, water-covered surface of Earth that obscures or obliterates these features and makes them very difficult to find.
"We can learn a lot from the smaller ones," he said. "I've seen some features in my samples that I haven't seen in literature. It's interesting to find a structure like this at all in a tropical setting, especially with the erosion rates as high as they are in the tropics."
The rocks that were hit by the asteroid are 20 million years old, so it's possible the impact could have occurred 20 million years ago. Tornabene wants to send some samples for Argon-Argon dating, a radioactive method to resolve the formation age of the impact structure.
The University of South Florida is a metropolitan research university with campuses in Tampa, St. Petersburg, Sarasota/Manatee and Lakeland. With about 35,500 students, USF offers 70 baccalaureate programs and 130 graduate programs, including the M.D. Last year, its students and faculty attracted $171.3 million in research contracts and grants.