Star Trek actor William Shatner, who played Captain Kirk, read the message from mission control in Houston, before it was beamed out to Voyager 1, according to a broadcast on NASA television.
"We offer friendship across the stars. You are not alone," said the message, written by Oliver Jenkins, whose Twitter handle is @Asperger_Nerd.
Forty years on, Voyager still hurtles through space
The contest launched by NASA aimed to find the perfect goodwill message -- under 60 characters long -- to commemorate the twin spacecraft that launched in 1977 from Cape Canaveral, Florida.
The spaceships explored Jupiter, Saturn, Uranus and Neptune, and also carried gold records containing messages, songs and images from Earth in case of encountering extraterrestrial life.
Record-breaking NASA astronaut comes back to Earth
Voyager 1 has traveled father than any human-made spacecraft, and made it to interstellar space, about 13 billion miles away from Earth, in August 2012.
Voyager 2 is on its way there too.
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