The most persuasive evidence that Voyager 1 has crossed the termination shock is its measurement of a sudden increase in the strength of the magnetic field carried by the solar wind, combined with an inferred decrease in its speed.

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The Sun's magnetic field and solar wind - mainly in the form of electrons and protons coming out of the Sun - protects the entire Solar System by acting as a sort of shield from cosmic rays (very energetic particles and radiation from outer space).

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It also found that Ganymede, the largest moon in the solar system, has a magnetic field.

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The idea of using a magnetic field as a solar sail was first suggested a few years ago, but it soon became apparent that creating a field strong enough to be useful would require exotic superconducting materials that, unfortunately, do not exist.

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These craft will study the interaction between the solar wind (the breeze of electrically charged particles emitted by the sun) and the earth's magnetic field.

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The portals, also known as X-points in Scudder-speak, are born from the mingling of Earth's magnetic field with incoming solar winds.

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And water would be all the more exciting on Ganymede because it is the largest moon in the solar system (larger even than the planets Mercury and Pluto) and, like earth, it has a permanent magnetic field that protects part of its surface from bombardment by certain sorts of life-destroying radiation.

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Was its magnetic field disrupted as the magma in its mantle cooled, exposing it to solar winds?

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