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Elvia H. Thompson
Headquarters, Washington            March 6, 2003
(Phone: 202/358-1696)

Alan Buis
Jet Propulsion Laboratory, Pasadena, Calif.
(Phone: 818/354-0474)

Eric Berryman
National Imagery & Mapping Agency, Bethesda, Md.
(Phone: 301/227-3132)

RELEASE: 03-096

NASA'S NEWEST MAPS REVEAL A CONTINENT'S GRANDEUR AND A SECRET

     From Canada to Central America, the many grandeurs of North 
America's diverse topography star in a just-released high-resolution 
map from NASA's Shuttle Radar Topography Mission (SRTM). But a 
relatively obscure feature, all but hidden in the flat limestone 
plateau of Mexico's Yucatan Peninsula, is what emerges as the initial 
showstopper from the mission's first released continental data set.

The existence of the impact crater, Chicxulub, was first proposed in 
1980. In the 1990s, satellite data and ground studies allowed it to 
gain prominence among most scientists as the long sought-after 
"smoking gun" responsible for the demise of the dinosaurs and more 
than 70 percent of Earth's living species 65 million years ago. The 
SRTM has provided the most telling visible evidence to date of a 
180-kilometer (112-mile) wide, 900-meter (3,000-foot) deep impact 
crater, the result of a collision with a giant comet or asteroid on
one of Earth's all-time worst days. 

The North America and Yucatan Peninsula images created from the map 
are available on the JPL Planetary Photo journal at: 

http://photojournal.jpl.nasa.gov/catalog/PIA03377
http://photojournal.jpl.nasa.gov/catalog/PIA03379

"This new, complete North American data set greatly expands our 
topographic knowledge of Canada, southern Alaska and its Aleutian 
Islands, Mexico and Central America," said Dr. Michael Kobrick, SRTM 
project scientist at NASA's Jet Propulsion Laboratory (JPL), Pasadena, 
Calif.

"There are spectacular features that pop out in these maps as never 
before, and more subtle features, like Chicxulub, become apparent for 
the first time. In fact, much of the surface expression of Chicxulub 
is so subtle; if you walked across it you probably wouldn't notice it. 
That's where the view from space becomes invaluable, " Kobrick said.

The Chicxulub data show a subtle, yet unmistakable, topographic 
indication of the impact crater's outer boundary: a semicircular 
trough 3 to 5 meters (10 to 15 feet) deep and 5 kilometers (3 miles) 
wide. Scientists believe the impact, centered off Yucatan's coast in 
the Caribbean, disturbed the subsurface rocks, making them unstable. 
The rocks were subsequently buried by limestone sediments, which erode
easily. The crater rim's instability caused the limestone to fracture 
along the rim, forming the trough. In addition, the collapse of 
numerous limestone caverns above the crater rim resulted in an arcing 
chain of sinkholes, called cenotes, that are visible as small, 
circular depressions. 

Exactly how the Chicxulub impact caused Earth's mass extinctions is 
not known. Some scientists think it threw massive quantities of dust 
into the atmosphere, blocking the sun and stopping plants from 
growing. Others believe sulfur released by the impact lead to global 
sulfuric acid clouds that blocked the sun and also fell as acid rain. 
Another possibility is global wildfires triggered by atmospheric
reentry of red-hot debris.

The remainder of the North American data paints a dynamic portrait of 
a geologically complex continent. Active structural deformations of 
Earth's crust along and near the Pacific/North American tectonic plate 
boundary create the diverse topographic relief of the Pacific coast. 
Across the Great Plains, erosional patterns dominate, with stream
channels surrounding and penetrating remnants of older smooth slopes. 
In Canada and the northern U.S., evidence of glaciers from the last 
ice age abounds. 

In February, NASA finished processing the mission's data and delivered 
it to the National Imagery and Mapping Agency (NIMA). More than eight 
terabytes of data recorded aboard the Space Shuttle Endeavour were 
refined into 200 billion research-quality measurements of Earth's 
landforms. The NIMA will perform additional data finishing and send it 
to the U.S. Geological Survey's Earth Resources Observation Systems
Data Center, Sioux Falls, S.D., for final archiving and distribution. 
South America will be the next continental dataset.

The SRTM, flown Feb. 11 to 22, 2000, made 3-D measurements of the more 
than 80 percent of Earth's landmass located between 60 degrees north 
and 56 degrees south of the equator; areas home to nearly 95 percent 
of the world's population. SRTM is a cooperative project of NASA, 
NIMA, the Department of Defense, the German and Italian space 
agencies. Fulfilling part of NASA's mission to understand and protect 
our home planet, it is managed by JPL for NASA's Earth Science
Enterprise, Washington. The California Institute of Technology in 
Pasadena manages JPL for NASA.

For more information about SRTM on the Internet, visit:
             http://www.jpl.nasa.gov/srtm/

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