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stellar space is near, but it could take days, months or years to cross that milestone.
• Voyager 1 is currently more than 11 billion miles from the sun. Twin Voyager 2, which celebrated its launch anniversary two weeks ago, trails behind at 9 billion miles from the sun.
• They're still ticking despite being relics of the early Space Age.
• Each only has 68 kilobytes of computer memory. To put that in perspective, the smallest iPod -- an 8-gigabyte iPod Nano -- is 100,000 times more powerful. Each also has an eight-track tape recorder. Today's spacecraft use digital memory.
• The Voyagers' original goal was to tour Jupiter and Saturn, and they sent back postcards of Jupiter's big red spot and Saturn's glittery rings. They also beamed

home a torrent of discoveries: erupting volcanoes on the Jupiter moon Io; hints of an ocean below the icy surface of Europa, another Jupiter moon; signs of methane rain on the Saturn moon Titan.
• Voyager 2 then journeyed to Uranus and Neptune. It remains the only spacecraft to fly by these two outer planets. Voyager 1 used Saturn as a gravitational slingshot to catapult itself toward the edge of the solar system.
• "Time after time, Voyager revealed unexpected -- kind of counterintuitive -- results, which means we have a lot to learn," said Stone, Voyager's chief scientist and a professor of physics at the California Institute of Technology.
• These days, a handful of engineers diligently listen for the Voyagers from a satellite campus not far from the NASA Jet Propulsion Laboratory, which built the spacecraft.
• The control room, with its cubicles and carpeting, could be mistaken for an insurance office if not for a blue sign overhead that reads "Mission Controller" and a warning on a computer: "Voyager mission critical hardware. Please do not touch!"
• There are no full-time scientists left on the mission, but 20 part-timers analyze the data streamed back. Since the spacecraft are so far out, it takes 17 hours for a radio signal from Voyager 1 to travel to Earth. For Voyager 2, it takes about 13 hours.
• Cameras aboard the Voyagers were turned off long ago. The nuclear-powered spacecraft, about the size of a subcompact car, still have five instruments to study magnetic fields, cosmic rays and charged particles from the sun known as solar wind. They also carry gold-plated discs containing multilingual greetings, music and pictures -- in the off chance that intelligent species come across them.
• Since 2004, Voyager 1 has been exploring a region in the bubble at the solar system's edge where the solar wind dramatically slows and heats up. Over the last

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