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Science & Space

Spacecraft reaches edge of solar system

By Kate Tobin

Voyager 1 travels roughly one million miles (1.6 million kilometers) a day.
Voyager 1 travels roughly one million miles (1.6 million kilometers) a day.

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(CNN) -- The Voyager 1 spacecraft has arrived at the boundary of the solar system and is flying into a region of space that has never been explored before, NASA announced Wednesday.

"This is a very exciting time, said Voyager project scientist Edward Stone. "Voyager is beginning to explore the final frontier of the solar system."

Scientists analyzing data from Voyager 1 disagree as to whether the probe has yet crossed over the critical boundary that marks the transition from our solar system into interstellar space. But even dissenters agree that if it has not crossed that boundary, called terminal shock, it is very close.

"We're in the neighborhood. This is sort of a Lewis and Clark space expedition: We're in the foothills, and we'll soon be getting to the mountains, in our view," said Frank McDonald, a research scientist at the University of Maryland.

Voyager 1's journey marks a major scientific milestone: For the first time, a man-made object has traveled 8.4 billion miles (13.5 billion kilometers), about 90 times the distance between the Earth and sun. Ahead lies the journey to the star next door. Traveling at its predicted speed, Voyager 1 will get there in about 40,000 years.

Launched in 1977, Voyager 1 and its twin, Voyager 2, were the first space probes to explore the outer planets of our solar system. Voyager 1's primary mission ended in 1980 when it completed its observations of Saturn. Since then, it has been headed into deep space. In 1998, it passed the Pioneer 10 space probe and became the most distant man-made object from Earth.

'First taste' of the beyond

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Now, scientists from the Johns Hopkins University's Applied Physics Laboratory and colleagues believe Voyager 1 crossed into the area marking the edge of the solar system.

"Voyager 1 is giving us our first taste of interstellar space," said Tom Krimigis, of the Applied Physics Laboratory, in a written statement. "This is our first look at the incredibly dynamic activity in the solar system's outer limits."

Contrary to popular belief, space is not an empty void. Rather, our solar system is awash in the solar wind, the charged gases that flow off our sun at supersonic speed. At the termination shock boundary, the solar wind dissipates and begins to give way to the interstellar medium -- the gases that float in the void between stars.

Instruments aboard Voyager 1 are able to measure the speed of the solar wind, and the Applied Physics Lab's analysis of that data suggests the spacecraft has hit the terminal shock boundary. The findings are published in the November 6 edition of the journal Nature.

A different view

A second article in Nature offers a more conservative analysis. The University of Maryland team interprets additional data from Voyager 1 to mean the spacecraft is approaching the termination shock boundary, but has yet to hit it.

Voyager's greeting to the universe is a phonograph record.
Voyager's greeting to the universe is a phonograph record.

"What we see, the observations agree very well with what Tom has described," said McDonald with the University of Maryland. "We just interpret them differently. That we're in the neighborhood of the termination shock, and we haven't crossed it."

Whichever the case, scientists are particularly excited as the 26-year-old probe still has operating scientific instruments. NASA says Voyager 1 still has enough power to beam back data through about the year 2020.

By that time, experts hope to also monitor the spacecraft's journey through something called the heliopause, the outer boundary delineating the edge of interstellar space. As these outer reaches of the solar system have never been explored, it is unclear exactly where these boundaries lie.

Voyager 1 and 2 both carry a so-called "golden record" -- a 12-inch gold-plated copper disk that is actually a phonograph record. The disk carries greetings and an overview of our culture to extraterrestrials that may one day stumble across one of these man-made craft.

The record includes samples of music; nature sounds such as thunder, waves crashing, bird songs; and greetings in multiple languages, including from then President Jimmy Carter and U.N. Secretary-General Kurt Waldheim. Pictographs on the disk explain how it should be played. A phonograph needle is included.

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