September 10, 2012

Bearing greetings from Earthlings now more than 11 billion miles (18 billion kilometers) away, the Voyager 1 spacecraft continued its epic trek to the edge of the solar system on September 5, 35 years after its launch into space. NASA had launched a companion craft, Voyager 2, on August 20, also in 1977. Together, the two probes have lasted longer and traveled farther than any other space probes in history. Voyager 2 is now about 9 billion miles (15 billion kilometers) from the sun, going south, the opposite direction from Voyager 1.

The space probe Voyager 2 was launched on Aug. 20, 1977. Its path through the solar system is shown in red. Voyager 2 flew past and photographed Jupiter in 1979, Saturn in 1981, Uranus in 1986, and Neptune in 1989. (World Book illustration by Ken Tiessen, Koralik Associates)

Initially, the two spacecraft were given a five-year mission to explore the gas giants Jupiter and Saturn. The data they sent back to Earth have answered many questions about the planets’ atmospheres, interiors, rings, magnetospheres (surrounding zones of strong magnetic fields), and satellite systems. With this part of the Voyager mission completed, engineers at NASA’s Jet Propulsion Laboratory in Pasadena, California, in 1981 decided to push the two craft farther into space. Voyager 2 became the first–and so far–only spacecraft to visit Uranus and Neptune. They found evidence of geologic activity on two previously known moons—volcanoes on Jupiter’s moon Io and icy geysers on Neptune’s moon Triton.

Since 1989, the two probes have been exploring the heliosphere, a vast, tear-drop-shaped region of space that contains the solar system, the sun’s magnetic field, and the solar wind (electrically charged particles given off by the sun). In late 2004, Voyager 1 crossed a shock wave called the termination shock, becoming the first craft to reach the region of space that lies just inside the heliopause (the final boundary of the solar system). The crossing occurred at a distance of about 8.7 billion miles (14 billion kilometers) from the sun. In 2007, Voyager 2 crossed the shock in a different area and at a distance of about 7.8 billion miles (12.6 billion kilometers) from the sun. By detecting the shock at different distances from the sun, the two craft confirmed scientists’ belief that the solar system is not perfectly round.

The two Voyager spacecraft explore the outer edges of the heliosphere, a vast, tear-drop-shaped region of space that contains the solar system, in an artist’s illuustration. (NASA/JPL-Caltech)

Scientists are not sure when Voyager 1 and 2 will leave the heliosphere and go where no spacecraft has gone before–interstellar space. Some signals from Voyager 1 suggest that the craft’s escape from the solar system may occur in the near future. Regardless, the two spacecraft will have enough electrical power to continue collecting data and communicating it back to Earth through 2020, and possibly through 2025.

Additional World Book articles:

• Space exploration
• The Thirty-Year Journey of Voyagers 1 & 2 (A Special Report)
• Astronomy (1979) (A Back in Time article)
• Astronomy (1989) (A Back in Time article)
• Space Exploration (1977) (A Back in Time article)
• Space Exploration (1979) (A Back in Time article)