What We Know About Voyager 1's One-Light-Day Milestone

A spacecraft launched during the Carter administration is about to outrun every other human-made object in history. On Wednesday, NASA's Voyager 1 probe is set to cross a distance of roughly 16 billion miles from Earth — the span light itself covers in 24 hours, or one light-day — according to Al Jazeera, which cited reporting from the Associated Press and Reuters.

No probe, satellite, or rocket stage built by any country has traveled this far from home. Voyager 1 left Cape Canaveral in 1977, swung past Saturn in 1980 to close out its primary planetary mission, and has spent the decades since pushing deeper into interstellar space — the region between star systems where the sun's influence fades.

How fast is Voyager 1 moving, and how far has it gone?

The probe is currently traveling at roughly 36,000 miles per hour, according to Al Jazeera's report. At that speed, reaching one light-day works out to about 16 billion miles of accumulated distance since launch — a figure NASA ties directly to Wednesday's milestone. For comparison, light takes about eight minutes to reach Earth from the sun; it takes a full day to cover the distance Voyager 1 has now traveled.

What is Voyager 1 actually doing out there?

It is still working. The plutonium-powered probe sends data back to Earth every day, including readings on the strength and direction of the surrounding magnetic field, ambient pressure, interstellar dust, and galactic cosmic rays, Al Jazeera reported. Voyager 1 project manager Suzanne Dodd compared the ongoing mission to a familiar earthbound task, telling the Associated Press that the two Voyager probes function much like weather satellites — quietly gathering environmental data long after the public stopped watching closely.

A skeleton crew of NASA engineers sends commands to the spacecraft roughly once a week, more often if something goes wrong. Dodd called Voyager 1 "a national treasure," a description that reflects both its scientific output and its unmatched longevity.

What happened when NASA briefly lost contact with Voyager 1?

In October, the team lost communication with the spacecraft for a period and has not yet determined the cause, according to the Al Jazeera report. The incident did not end the mission — contact was restored — but it underscores how fragile the link to a 49-year-old spacecraft can be at a distance where a single radio signal takes roughly 22 hours to arrive. Each unexplained lapse adds urgency to a question NASA's team cannot fully answer: how much longer the aging hardware and its dwindling power supply can keep responding.

Why does the Pale Blue Dot photo keep coming up?

Because it is the moment most people associate with this mission. In 1990, as it traveled outward, Voyager 1 turned its camera back toward Earth and captured the image known as the "Pale Blue Dot" — a single pixel of light against the dark. Bill Nye, of the Planetary Society, framed the probe's reach in human terms in a statement cited by Al Jazeera: "All of us — everyone on Earth — have been touched by these missions."

Voyager, by the numbers

• 16 billion miles: distance Voyager 1 will have traveled as of Wednesday, equal to one light-day
• 36,000 mph: Voyager 1's current speed through interstellar space
• 1977: year both Voyager 1 and Voyager 2 launched
• 18,000 years: time NASA projects Voyager 1 will need to travel a full light-year
• 2035: year Voyager 2, launched shortly before its twin, is expected to reach its own one-light-day mark

What's next for Voyager 1 and Voyager 2?

Voyager 2 is trailing behind on a different trajectory and is not expected to hit the one-light-day mark until 2035, per Al Jazeera's report. Both probes will keep sending data for as long as their plutonium power sources and NASA's small engineering team can sustain contact.

What to watch:

• Whether NASA's team identifies the cause of October's brief communication lapse with Voyager 1
• How much longer engineers can keep both probes' instruments powered as plutonium output declines
• Voyager 2's progress toward its own one-light-day milestone in 2035
• Any additional statements from NASA or the Planetary Society marking the anniversary

NASA has not released a specific end date for either mission, and officials continue to treat each year of continued contact as its own result rather than a foregone conclusion.