Robotic probes have landed on three planets, two moons, and two asteroids. They've swooped to within a few thousand miles of each of the other planets, a passel of moons, and a handful of asteroids and comets. In fact, the biggest object in the solar system that hasn't had a close visit by a probe is...the biggest object in the solar system: the Sun.
It's so hot, and it produces so much radiation, that no spacecraft has flown closer than about 30 million miles above its searing surface. But that could change in about 15 years, because NASA's approved a mission to fly just four million miles from the Sun.
Solar Probe will fly well within the Sun's outer atmosphere, called the corona. It's thin, but it's heated to more than a million degrees by the Sun's magnetic field.
As it skims past the Sun, Solar Probe will measure the corona and the magnetic field. It'll also measure the solar wind -- a steady flow of charged particles from the surface of the Sun. And it'll study the processes that create the corona and the solar wind.
Solar Probe will scrunch behind a thick shield made of material that's similar to some of the protective skin of a space shuttle. The shield will be subjected to about the same maximum temperature as a shuttle -- 2600 degrees Fahrenheit. And it'll be bombarded by radiation and the steady flow of the solar wind. But if it holds up, it'll give us our closest view yet at the dominant member of the solar system.
Script by Damond Benningfield, Copyright 2008
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