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JET PROPULSION LABORATORY
CALIFORNIA INSTITUTE OF TECHNOLOGY
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PASADENA, CALIFORNIA 91109. TELEPHONE (818) 354-5011
http://www.jpl.nasa.gov http://www.jpl.nasa.gov/

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

Elvia H. Thompson  (202) 358-1696
NASA Headquarters, Washington, D.C.

Eric Berryman  (301) 227-3132
National Imagery and Mapping Agency, Bethesda, Md.

News Release: 2003-030                  March 6, 2003  

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.  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 known as Chicxulub (Chik-sah-loob)
was first proposed in 1980.  In the 1990s, satellite data and ground
studies allowed it to gain prominence among many 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.  Now, the Shuttle Radar Topography Mission 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 Photojournal at:
http://photojournal.jpl.nasa.gov/catalog/PIA03377 and
http://photojournal.jpl.nasa.gov/catalog/PIA03379 , respectively.

"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,
Shuttle Radar Topography Mission project scientist at NASA's Jet
Propulsion Laboratory, Pasadena, Calif.  "There are spectacular
features that pop out at you 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 that
if you walked across it you probably wouldn't notice it.  That's where
the view from space becomes invaluable."

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 led to global
sulfuric acid clouds that blocked the Sun and 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 United States, 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.  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 National Imagery and Mapping Agency 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.  The next continental data set
to be released will be of South America. 

The Shuttle Radar Topography Mission, 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.  The
mission is a cooperative project of NASA, the National Imagery and
Mapping Agency of the U.S. Department of Defense, and 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, D.C.  The California
Institute of Technology in Pasadena manages JPL for NASA.

More information on the mission may be found at:
                 http://www.jpl.nasa.gov/srtm/ .

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