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Space Scientists to Give Earth a Physical Checkup : Environment: Current, new satellites will help NASA examine planet's health. Many call effort long overdue.


It is a scene right out of the ER: Good old Earth, every square foot of her scrutinized continuously by a constellation of spies in the sky, hooked up like an intensive-care patient to high-tech instruments keeping track of every bulge and burp, cough and sputter, heave and sigh; her vital gases measured; her vital fluids tracked; her plumbing checked for leaks and overflows; her intimate history uncovered.

Will she make it through the night? That is the question about to be posed by an ambitious NASA effort to diagnose the health of our home planet.

The folks who brought us the flashy planetary probes that phoned home dramatic images of Mars, Jupiter, Uranus and Venus are now turning their sights inward. Called Mission to Planet Earth (MTPE), the effort is a combination of current shuttle- and satellite-borne instrumentation, and a series of planned new satellites that will make up the Earth Observing System (EOS).

Collectively, they will scrutinize Earth more doggedly and in more detail than ever before.

In the process, the mission will try to answer some increasingly urgent questions:

* Is the Earth about to suffocate under its carbon dioxide sheet? Heat trapping gases such as carbon dioxide buildup in the atmosphere due to burning of fossil fuels and deforestation.

* Will it fry under its badly damaged ozone umbrella? Fluorocarbons manufactured on Earth break up the fragile ozone layer that screens out cancer-causing ultraviolet rays.

* Will it be poisoned by its own pollution? People and industries dirty the air and water with their non-recyclable wastes.

* Will it melt under the cumulative impact of ice sheets turning to water that floods coastal communities? Warming temperatures make sea levels rise.

* Or is continual wearing down by destructive agriculture practices a more clear and present danger? Clear-cutting and erosion destroy topsoils and eat away at fertile areas amenable to human habitation.

Even though no one knows for sure what ails the planet, the possible prognoses seem too dire not to check out.

Many scientists and environmentalists think this kind of introspective effort is long overdue. Researchers know surprisingly little about the health of their planet. They know more about the sun--93 million miles away. They know more about the landscape of Venus, even though that planet is shrouded in thick, acid clouds.

In fact, it was the grand success of space missions to Venus and Mars that turned geologists into virtual astronauts, studying the Earth from space instead of with hiking boots and hammers. "The Viking missions got us used to looking at planets with remote-sensing technology," said geologist Diane Evans, project scientist with Mission to Planet Earth. "They made us think about new ways of looking at Earth."

NASA and foreign space agencies have been road-testing increasingly sophisticated satellites and other instruments for monitoring Earth since the late 1970s. With satellites that can penetrate political and geographic boundaries with impunity, they have yielded some spectacular results.

Tantalizing recent finds have included lost cities buried in the dust, ancient riverbeds under the Sahara and secret habitats of gorillas in the African mist. Satellites have also tracked the birth and development of El Nino currents responsible for wacky weather patterns, seen bulges in the ground that might predict volcanic eruptions and followed the formation of eddies in the Gulf of Mexico dangerous enough to topple oil rigs. They have uncovered hidden mineral deposits, subtle motions of continental plates and patterns of snowmelt in glaciers.

But many of these efforts were one-shot projects, or limited in scope, rather than part of sustained efforts to monitor the vital signs of the entire globe. Scientists say there is a lot more to learn. "In many ways, we're just beginning," said Charles Kennil, head of Mission to Planet Earth.

The Earth is a much more complex organism than either the sun or Venus, which makes studying it all the more difficult. The sun is composed primarily of hydrogen and helium. The Earth contains at least 22 elements in significant amounts and in a bewildering variety of forms. Venus has no running water or oceans to muddy up features. On Earth, plants, insects, animals and microorganisms continuously metabolize elements in complex webs that are far from understood.

Because everything is interrelated on Earth, it can be difficult to disentangle causes and effects. Everything is changing: As the Earth turns from day to night, it breathes oxygen and carbon dioxide in global respiratory rhythms; when the continents shift, they can take ocean sediments and deposit them on snowcapped peaks; as a rain forest digests sunlight and minerals, it feeds them to birds that spread seeds far and wide; when a city metabolizes rubber and oil and hot dogs, it regurgitates pollutants that linger in the sky.

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