[meteorite-list] USF Graduate Student Confirms Asteroid Impact Site In Panama

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu Apr 22 09:43:29 2004
Message-ID: <200107061455.HAA06103_at_zagami.jpl.nasa.gov>

U.South Florida graduate student confirms asteroid site in Panama

University of South Florida

Media Contact:
Marsha Strickhouser, (813) 974-4014

STORY SOURCE:
Livio Tornabene, (813) 598-4231

June 18, 2001

USF graduate student confirms asteroid site in Panama

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.
Received on Fri 06 Jul 2001 10:55:03 AM PDT