Voyager 1 Is About to Be One Full Light Day Away From Earth

Keypoints:

• Voyager 1 reaches one light day from Earth on November 18
• That's about 25.9 billion kilometers, or 16.1 billion miles
• Radio signals will take a full 24 hours to reach it
• Voyager 2 won't get there until November 2035
• Engineers are managing low power and odd technical glitches

Voyager 1 is about to hit a milestone no human made object has ever reached. On November 18, NASA says, the probe will be one light day from Earth, meaning a radio signal sent from here takes a full 24 hours just to arrive. Some outlets give a day either side, depending on how they time it.

That works out to about 25.9 billion kilometers, or roughly 16.1 billion miles, which is around 173 times the distance between Earth and the sun. Voyager 1 launched on September 5, 1977, and it took 49 years, 2 months and 11 days to get that far. It flew past Jupiter and Saturn first, then crossed out of the sun's influence into interstellar space back in 2012.

For perspective, Voyager 2 won't reach one light day until November 2035. Neptune sits only about four light hours from the sun, so a full day puts Voyager 1 far beyond anything else we've sent.

Nothing physically changes on board when it crosses the line. What changes is the conversation. A command sent from mission control takes a day to arrive and the reply takes another day to come back, so every back and forth now takes about two days. Engineers have been working around that for a while, and they've also been fighting dwindling power and some strange technical problems. A clever energy saving move has helped stretch the spacecraft's science work a bit longer, but power is expected to run out in the early 2030s.

Even then, Voyager 1 keeps going. It's headed toward a star called Gliese 445, and in about 40,000 years it will pass within roughly 1.7 light years of it, according to the mission team. It's a nice reminder that a spacecraft built with 1970s technology is still sending back data nearly 50 years later.