Voyager 1 -- Launched in 1977, on Verge of Exiting Solar System

On Dec. 13, 2010, NASA space probe Voyager 1 reached a point on the far edge of our solar system. At 10.8 billion miles from the sun, Voyager 1 has nearly encountered the farthest reach of the solar winds, which are hot ionized gas particles emanating from the sun, and is getting closer to exiting the solar system.

Since passing Saturn in 1980, Voyager has charted a lonely path across the remainder of our solar system, while its twin Voyager 2 went on to visit Uranus and Neptune. Both are now beyond the orbit of Pluto, and Voyager 1 could reach the edge of interstellar space, known as the heliopause, as soon as 2014.

Volcanoes on Io

During its 33-year mission, Voyager 1 has made many significant discoveries. Originally designed to last for five years and explore Jupiter and Saturn, Voyager 1 was the first to fly by Jupiter's moon Io. In its transmissions back to Earth, Voyager 1 showed that Io was tremendously active with at least six erupting volcanoes on its surface. Io's existence was known as early as 1610 after its discovery by Galileo, but its volcanic activity hadn't been guessed until the volcanic plumes were discovered during both Voyagers' flybys. And, even more startling, the volcanic eruptions didn't appear to be present when the earlier Pioneer probes flew by four years earlier!

Composition of Saturn's Atmosphere

Voyager 1, in measuring the upper atmosphere of Saturn, determined that its upper atmosphere differed from that of Jupiter. Whereas Jupiter's upper atmosphere consists of 11 percent helium and the remainder hydrogen, Saturn's upper atmosphere consists of only 7 percent helium and the remainder hydrogen, suggesting that if a body of water existed large enough to contain Saturn, the planet would float.

Scientists also hypothesized from Voyager's transmissions that Saturn's helium is sinking toward the planet's core, resulting in an increase in temperature over what it receives from the sun.

Journeying through the Heliosheath

Most recently, Voyager 1 has already crossed the termination shock, the point in the solar system which divides the area of intense solar winds from an area that marks the sun's furthest reaches, and is now in the heliosheath. The heliosheath, according to NASA, is the region in the solar system in which the solar winds drop to zero, and the interstellar wind increases.

Eventually, originally predicted to be within the next 10 years or so, Voyager is slated to cross the heliopause, which is the point at which the solar winds and interstellar winds are in balance. At this point, Voyager will leave our solar system. What is remarkable is that Voyager 1 has already reached a point where the solar wind velocity has reached zero, suggesting that its departure from our solar system is imminent and much closer than previously predicted.

These are truly remarkable discoveries from space probes that were originally only designed to last for a brief few years, but are now anticipated to reach their 47^th birthday before their batteries finally die.

Sources:

Hamilton, Calvin. (2009). Solarviews: IO.
Cook, Jia-Rui. (2010). NASA Probe Sees Solar Wind Decline. NASA.
NASA. (2010). Voyager: Interstellar.
NASA. (2010). Voyager: Saturn.