Gliese 581c’s 2050 Reply Window

On October 9, 2008, humans beamed a high-powered digital radio signal called "A Message from Earth" toward the exoplanet Gliese 581c, about 20.5 light-years away. The signal should reach the system in early 2029, simply because radio travels at light speed. If anything there answered immediately, Earth would not hear the first possible reply until about 2050.

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