How Voyager Works

To Neptune and Beyond
Jupiter's Great Red Spot, which extends from the equator to the southern polar latitudes, as seen by the space probe Voyager 2 in 1979.
Jupiter's Great Red Spot, which extends from the equator to the southern polar latitudes, as seen by the space probe Voyager 2 in 1979.
MPI/Hulton Archive/Getty Images

Although the lifetime mission cost for Voyager exceeded $750 million, by 1989 the spacecrafts had returned enough scientific data to fill 6,000 editions of the Encyclopedia Britannica [source: Evans]. The science modules on board were chosen from proposals submitted by research teams across the United States. The information about Jupiter, Saturn, Uranus and Neptune (and many of their moons) that we learned from the Voyager missions wasn't just vast in quantity, but also in influence. It shaped science textbooks in schools across the U.S., informed public perceptions of the solar system and laid the foundation for the modern space program. Much of what we know about the outer planets came from Voyager. That’s not to mention the thousands of photographs taken from vantage points humans had never experienced before. Those brilliant images of Jupiter and Saturn fired the public’s imagination and fueled enthusiasm for future space exploration.

From Voyager, we learned more about the weather on Jupiter; the rings around Jupiter, Saturn and Uranus; volcanic activity on Jupiter's moon Io; the masses and densities of Saturn’s moons; the atmospheric pressure on Titan, Saturn's largest moon; the magnetic field of Uranus; and a persistent weather system on Neptune as large as Earth, known as the Great Dark Spot. By the time Voyager 2 reached Neptune, it was 1989. More than 10 years had passed since launch, and many of the scientists working on the original mission had moved on. Voyager had passed by Jupiter, Saturn and Uranus in 1979, 1981 and 1986, respectively.

The Great Dark Spot on the surface of Neptune, as observed by the Voyager 2 spacecraft in 1989. The spot, thought to be a swirling mass of gases, had disappeared by 1994, to be replaced by a similar spot in a different location.
Space Frontiers/Hulton Archive/Getty Images

So where are they now? The two Voyagers aren't together. Voyager 1 is moving north (relative to the orientation of Earth out of the solar system), while Voyager 2 is moving south. In 2007, they both entered the heliosheath, the outermost section of the solar system. There, the solar wind meets interstellar magnetic fields and forms a boundary with a shock wave. The Voyagers traversed the shock wave and sent data back, giving astronomers their first idea of the shape and location of the heliosheath. On Sept. 21, 2013, Voyager scientists reported that Voyager 1 left the solar system on Aug. 25, 2012.

Although some instruments on the Voyagers are no longer working, they do continue to send back important information. Imagine a car that has been on the road continuously since 1977, and you'll get some idea of how amazing these spacecraft are. At their current distance, it takes radio signals traveling at the speed of light more than 14 hours to reach Earth. The craft are running low on fuel for their orienting thrusters and will have to power down some instruments in the coming years as their plutonium runs out as well. By 2020, they will be dark and silent.

Yet they will continue on their current trajectory, moving over 30,000 mph (48,280 km/h), arcing out into the Milky Way for tens of thousands of years. With no atmosphere in space, they will never corrode, and there is little for them to crash into in interstellar space. It will take them about 40,000 years before they even come within light years of another star. The Voyagers may be traveling for hundreds of thousands or even millions of years.

What if the Voyagers meet an intelligent alien civilization some day? We’ve left a message for them.