We can harness the solar wind to sail to the farthest corners of space

JOHANNES KEPLER is remembered for writing down the laws of planetary motion. But the 17th-century astronomer also liked to observe comets and, one day, he noticed that their tails always pointed away from the sun, no matter which direction they were travelling in. To Kepler, it could mean only one thing: the comet tails were being blown by a wind from the sun.

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