On November 18 at 2:16 a.m. Pacific time, Voyager 1 will become the first human-made object to reach one light-day from Earth, according to NASA. That is 25,902,068,356 kilometers, or the distance light travels in 24 hours.
The milestone makes the mission’s communication lag unusually easy to picture. Radio signals move at light speed, so a command sent from Earth will need roughly a day to reach the spacecraft. A response will take another day to return.
A 49-year trip through the outer solar system
Voyager 1 launched in 1977 alongside its twin, Voyager 2. The probes used a rare planetary alignment to tour the outer solar system, with Voyager 1 flying past Jupiter and Saturn. Their cameras documented storms, rings and previously unseen moons. A navigation image from Voyager 1 also revealed a volcanic plume rising from Jupiter’s moon Io, the first active volcanism found beyond Earth.
The spacecraft overtook Pioneer 10 in 1998 to become the most distant human-built object. Its cameras were switched off after a final look back at the planets in 1990, which produced the “Pale Blue Dot” image of Earth. Turning the cameras off conserved power for the instruments that could still study the environment ahead.
Still doing science beyond the heliopause
Voyager 1 crossed the heliopause, the boundary of the sun’s protective particle bubble, on August 25, 2012. That made it the first spacecraft to enter interstellar space, though the sun’s gravitational influence extends much farther.
The region has been quieter than the space inside the heliosphere, but it has not been featureless. Science News reports that scientists have measured four episodes in which magnetic-field strength and particle density spiked around the probe. Both readings have remained elevated since the fourth event in mid-2020, and researchers do not yet know why. One possibility is that Voyager is detecting the lingering effects of solar eruptions, but that explanation remains a hypothesis.
Voyager 1 is still sending data home as its onboard power supply declines. Scientists estimate that its instruments may have another 10 to 15 years before the spacecraft can no longer return data. After contact ends, it will continue outward carrying its Golden Record, a time capsule of images, sounds and greetings from Earth.
