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Voyager 1 is about to reach a milestone: one light-day from Earth, after nearly 50 years of travel. On November 18, 2026, it is expected to become the first human-made object to be one light-day from Earth, roughly 16.1 billion miles (25.9 billion kilometers) away. Yet the distance matters mostly because of what the spacecraft discovered along the way. When Voyager 1 launched in 1977, its destination was the outer planets. At Jupiter, it revealed active volcanoes erupting on Io, the first ever seen beyond Earth. A moon once known only as a distant point of light turned out to be a world with a changing surface. At Saturn, it studied the intricate rings and the thick atmosphere surrounding Titan. That encounter bent its path upward, out of the plane where most planets orbit, and sent it toward the space between the stars. The planetary visits ended, but the journey did not. For decades, Voyager traveled through the vast region dominated by the solar wind, the stream of charged particles that flows outward from the Sun. In 2012, its instruments detected a transition: particles from the Sun dropped off, while particles arriving from beyond the solar system increased. Plasma measurements helped confirm that Voyager had entered interstellar space. It had crossed the heliopause, the outer boundary of the solar wind's influence, and begun sampling an environment that no spacecraft had ever reached. That is why its journey is more than a distance record. Voyager carried instruments into places we had only studied from afar, then sent back evidence of what is actually out there. Today, every message must travel across almost a full day of space at the speed of light, so a command and its reply take roughly two days. The spacecraft that showed us erupting moons and Saturn's rings is still teaching us about the space beyond the Sun's protective bubble.