Russian billionaire Yuri Milner and physicist Stephen Hawking announced the Breakthrough Starshot initiative last year, a $100 million program to develop technologies for small robotic nanoprobes and light beams with the power to accelerate to 20 percent of the speed of light. That's fast enough to reach the nearest star system within a generation.

When Breakthrough Starshot was first announced, even Facebook's co-founder and CEO Mark Zuckerberg joined the exciting project and became a member of the board.

The goal is to accelerate these ultralight nanocrafts, which are about the size of a postage stamp, to speeds up to 100 million miles an hour. At that velocity, they'll have the capability to reach the neighboring star system Alpha Centauri (located about four light years from Earth) relatively quickly. There, these tiny space probes could reach Proxima b, the closest known Earth-like exoplanet, about 20 years after they're launched.

One day, these miniature spacecraft should also carry astronauts.

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