Twenty-five miles up, Earth's atmosphere is thin and frigid. It's bombarded by radiation from the Sun, which changes the air's chemistry. It's also bombarded by tiny meteorites. In other words, it's a lot like conditions at the surface of Mars.
Last June, scientists took advantage of those conditions by launching instruments into the stratosphere with a giant balloon. The instruments not only tested the rarefied air, they also helped the scientists test the technology for future missions to Mars itself.
The flight was one of more than a dozen balloon-based missions last year. They counted cosmic rays from exploding stars, looked at the afterglow of the Big Bang, and searched for evidence of dark matter and antimatter. Missions planned for this year will study the Sun's magnetic field and the particles between galaxies.
Balloons offer a cheap alternative to satellites. They can carry scientific instruments above most of Earth's atmosphere, allowing them to see particles and energy that don't reach the surface. They can stay aloft for weeks at a time. And they cost only a fraction as much as satellites.
NASA launches balloons from Texas, New Mexico, Sweden, and Antarctica. The Antarctic balloons circle the South Pole, remaining airborne for up to six weeks at a time.
Future balloons may stay aloft for up to three months -- learning about the universe from high in the stratosphere.
More about balloon missions tomorrow.
Script by Damond Benningfield, Copyright 2009
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