Sky Doctor.

Getting a physical check up may be routine for you, but what about for planet Earth? It's not easy to examine more than 2 billion square kilometers (770 million square miles) of land, ice, and sea! Now Terra, NASA's newest satellite, may be just what the doctor ordered.

Launched in December 1999, the school-bus-sized Terra (Latin for "Earth") will monitor phenomena on Earth, from air pollution and weather patterns to wildfires and deforestation. Recently several satellites like Landsat 7 have observed Earth by remote sensing--scanning from 700 km (435 mi) above the planet. But these satellites were designed to focus on a single piece of Earth's puzzling phenomena, such as hurricanes, clouds, or the ozone layer. "Terra is the first satellite that looks at Earth as one full system, in the same way a doctor examines a full person," says Yoran Kaufman, Terra Project Scientist at NASA's Goddard Space Center in Greenbelt, Md.

The 4,800 kg (10,560 lb) satellite features five main surveillance instruments, which will focus on physical properties of land, air, the Earth's cryosphere (ice), and the oceans. For example, Terra will report on exactly how much vegetation, sunlight, pollutants, fire, and snow are distributed over the planet. The "sky doctor" should send a total of 850 gigabytes (one billion bytes, equal to about 100,000 college textbooks) of data and images to scientists each day.

One critical issue scientists hope to learn more about is how humans have impacted Earth's landscape and atmosphere: Does burning fossil fuels, like coal and oil, heat up the atmosphere? Does deforestation--the cutting of trees for commercial use--alter the amount of breathable oxygen for humans? "Terra is the earth-science equivalent of the Hubble Space Telescope," says Michael King, senior mission scientist. "It's going to really open our eyes."