NASA's Voyager near Solar System's edge

NASA's Voyager 1 probe is nearing the edge of our solar system after 33 years and nearly 11 billion miles of spaceflight.

The spacecraft may make the final crossing into interstellar space in just four more years, NASA announced yesterday.

The Voyager 1 spacecraft has entered a region of space in the outer solar system where the speed of solar wind – charged particles streaming from the sun – is effectively zero.

NASA scientists think the steep drop in solar wind speed is a sign that it has been blown sideways by a more powerful interstellar wind that blows in the spaces between stars.

"The solar wind has turned the corner," said Ed Stone, Voyager project scientist based at the California Institute of Technology in Pasadena, Calif, "Voyager 1 is getting close to interstellar space."

Voyager 1 has traveled about 10.8 billion miles (17.4 billion kilometers) from the sun since it launched on Sept. 5, 1977 on a mission to swing by the gas giant planets of Jupiter and Saturn.

But Voyager 1 did not stop there. It continued on its way and in 2004 crossed a solar system boundary known as the termination shock – the border at which the sun's supersonic solar wind crosses a shockwave, slows down and heats up.

The region immediately beyond the termination shock, where Voyager 1 is now, is called the heliosheath. The edge of the solar system is a cosmic border known as the heliopause.

The heliosheath forms a turbulent outer shell of the sun's cosmic reach, which scientists call its "sphere of influence." Once Voyager 1 travels beyond the heliosheath and crosses the heliopause, it will officially be in interstellar space.

The spacecraft is hurtling toward the solar system's edge at a steady rate of about 38,000 mph (61,155 kph).

NASA thinks Voyager 1 could cross into the interstellar frontier by 2014. When the probe makes the crossing, there should be a sudden drop in the amount of hot particles Voyager 1 encounters and a spike in the number of cold particles it detects, NASA officials said.

The observations were presented yesterday at the fall 2010 meeting of the American Geophysical Union meeting in San Francisco.

Voyager 1 was actually one of two spacecraft launched in 1977 to explore the outer solar system. On Aug. 20 of that year, just a few weeks before Voyager 1's launch, NASA launched Voyager 2 on a grand tour of the solar system that flew by Jupiter, Saturn, Uranus and Neptune. Both spacecraft rely on nuclear power sources to generate electricity.

http://www.space.com/scienceastronomy/nasa-voyager-1-leaving-solar-system-101213.html