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Moon and Jupiter
As far as anyone knows, the giant planet Jupiter is lifeless. But if anything did live there, it would have a pretty good shield against invaders from Earth or other planets: radiation belts that are a million times greater than Earth's.
As Jupiter rotates on its axis, the layers deep in its interior rotate at different speeds, producing a powerful magnetic field; more about that tomorrow.
The magnetic field traps charged particles from the Sun. It also creates charged particles by bombarding the atmosphere of the moon Io, which contains particles from Io's hundreds of volcanoes.
These particles form a doughnut around the planet's middle -- the radiation belts.
Without strong shielding, a person passing through the belts would be bombarded with a fatal dose of radiation in minutes.
And the conditions aren't much better for robotic spacecraft -- passage through the belts would fry all of their electronics in minutes. So designers must use special materials and heavy shielding to protect a craft's delicate innards.
And even then, the doses add up. When the Galileo spacecraft orbited Jupiter in the 1990s, it flew directly through the radiation belts only a few times. Yet by the end of the mission, its electronics were suffering from serious cases of radiation sickness -- induced by the "shield" around this giant planet.
Look for Jupiter to the lower right of the Moon at first light tomorrow. It looks like a brilliant star.
Script by Damond Benningfield, Copyright 2011