Voyager 1 Becomes First Human-Made Object to Reach One Light-Day From Earth

NASA has announced that its Voyager 1 probe will soon become the first human-made object to travel one light-day from Earth, according to Al Jazeera. The milestone is due on Wednesday, when the spacecraft will have covered at least 16 billion miles since its launch in 1977.

A light-day is the distance light travels in 24 hours. Voyager 1 is still sending data home, and NASA says its sister probe, Voyager 2, is expected to reach the same mark in 2035.

What a light-day measures

Astronomers often describe huge distances by how long light takes to cross them. One light-day is the distance covered in a single day, and for Voyager 1 that works out to at least 16 billion miles of travel.

The probe completed its flyby of Saturn in 1980, which ended its primary planetary mission. It has kept going ever since and is now moving at roughly 36,000 miles per hour through interstellar space, the vast gap between stars.

How slow the journey still is on a cosmic scale

Even at that speed, the distances involved are enormous. NASA expects it to take Voyager 1 18,000 years to cover a full light-year, and about twice that long before it comes near another star, according to Al Jazeera.

Voyager 1, powered by plutonium, was launched shortly before Voyager 2. Both probes continue to relay data to Earth every day. Their instruments measure the strength and direction of the magnetic field, as well as the surrounding pressure, dust and galactic cosmic rays.

A small team keeping two old spacecraft alive

The two probes are kept active by a skeleton team of NASA engineers. They send commands roughly once a week, and more often if a probe runs into trouble.

Trouble did arrive recently. In October, the team briefly lost communication with Voyager 1, and the engineers have not yet worked out why, Al Jazeera reported.

Suzanne Dodd, the Voyager 1 project manager, called the spacecraft “a national treasure” in comments to The Associated Press. She said the work the two probes do is comparable to that of weather satellites.

Why it matters

For most people, a probe passing a distance marker in space has no effect on daily life. But the milestone shows how long a probe launched in 1977 can keep working, and how much it can still teach scientists about the space between the stars.

The readings the probes send back include the strength and direction of the magnetic field, the surrounding pressure, dust and galactic cosmic rays, and both spacecraft relay them to Earth daily.

The missions have also left a mark on culture. The famous “Pale Blue Dot” photo of Earth was taken by Voyager 1 in 1990. Bill Nye of the Planetary Society said in a statement: “All of us — everyone on Earth — have been touched by these missions.”

What happens next

Voyager 1 will keep moving outward and, on Wednesday, pass the one light-day mark. Voyager 2 is expected to follow in 2035. The small NASA team will continue sending commands about once a week, and will keep looking for the cause of the October communication loss.

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Around Prague, based on reporting by Al Jazeera