This Wednesday (Nov. 18), humanity's most distant spacecraft will hit a new milestone. NASA's Voyager 1 probe, which has been exploring our solar system at increasingly remote depths since 1977, will reach 16.09 billion miles (25.89 billion kilometers) from Earth — a distance so vast, it takes light 24 hours to traverse the space between Voyager and our planet.
While we celebrate this achievement on Earth, Voyager 1 will observe its "light-day" in darkness; mission scientists turned off the probe's camera in 1990, immediately after it snapped its iconic "Pale Blue Dot" and "Solar System Family Portrait" images from beyond the orbit of Neptune. But before that, Voyager 1 had already taken tens of thousands of images of our cosmic neighborhood, and some of them totally transformed our understanding of the outer planets.
One of the most significant pieces of Voyager 1's legacy is its trip to Jupiter. From January to April 1979, the probe observed the solar system's largest planet and several of its giant moons up close, reaching a minimum distance of 174,000 miles (280,000 km) in March 1979, according to NASA. As it approached, Voyager snapped a photo of the gas giant every 96 seconds to create this incredible time-lapse movie of Jupiter's turbulent atmosphere.
Voyager observed discrete bands of Jupiter's atmosphere spinning at various speeds and in different directions, like a cosmic Rubik's Cube being twisted by an invisible hand. Clouds speed by as if on conveyor belts as giant, planet-size storms swirl.
Voyager's time-lapse film captures about 60 full days on Jupiter — the equivalent of about a month on Earth, since each Jupiter day is roughly 10 Earth hours —- providing the most comprehensive and high-resolution look at the planet yet. The observations significantly built on the data captured by NASA's Pioneer 10 and 11 Jupiter probes, which launched half a decade prior, showing the planet's atmosphere to be much more dynamic than astronomers realized.
Just before making its closest approach to the planet, Voyager spotted something remarkable: Jupiter had a thin, faint ring system. Made primarily of dust, the rings appeared only when Voyager saw Jupiter backlit by the sun. No telescope had ever seen this before, but ground-based observatories soon confirmed the rings' existence, and Voyager 2 took even clearer pictures of the rings when it reached Jupiter in July 1979.
We now know that all four outer planets — Jupiter, Saturn, Uranus and Neptune — have rings. Today, scientists suspect Jupiter's dusty rings are replenished partially by volcanic eruptions on the planet's volatile moon Io.
This discovery, too, can be linked to Voyager. While making a close approach to Io, the spacecraft witnessed the first-ever volcanic eruption on a world beyond Earth. This observation showed that moons, not just planets, can be geologically active. In this image, a giant volcano called Loki Patera (the largest volcano on Io, measuring an estimated 125 miles, or 200 km, wide) spews its guts into space.
Taken together, these observations of Jupiter and its moons showed the largest planet and its moons to be a far more dynamic, complicated and chaotic system than anyone had realized. Moreover, the close-up views of these distant worlds made them more than just dots in the sky. It made them fully realized worlds — places to explore, map and eventually visit. Just this week, China's space agency announced its intention to send a lander to Jupiter's moon Callisto in the first-ever landing mission to the Jovian system.
Voyager 1's work continues in interstellar space, which it officially reached in 2012. With its camera off, it studies the radiation environment of space using magnetic field and plasma detectors — the last two of its 10 science instruments still receiving power. Scientists suspect the legendary probe will fully run out of power in the 2030s.
For more stunning space photos, check out our Space Photo of the Week gallery.
