Voyager races across solar system, but just how far?

Twenty-six years and more than 8 billion miles from Earth, NASA’s durable Voyager 1 spacecraft has journeyed a greater distance than an...

Twenty-six years and more than 8 billion miles from Earth, NASA’s durable Voyager 1 spacecraft has journeyed a greater distance than any other man-made object, but scientists are not sure exactly what it has encountered at the far frontier of the solar system.

One team of scientists reported on Wednesday that radioed data show that the spacecraft apparently ventured across a turbulent boundary near the edge of the solar system, where supersonic winds of charged particles from the Sun collide with matter from interstellar space. No spacecraft has ever come close to the boundary, known as the termination shock.

At the same time, other scientists examining Voyager data argued that the boundary still lies ahead, though perhaps not too far. The conflicting views were aired at a news conference at the NASA in Washington and are the subject of articles published in the journal Nature.

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The team led by Dr Stamatios M. Krimigis of the Applied Physics Laboratory of Johns Hopkins University described sharp changes in the velocity of the solar wind that Voyager 1 began flying through in August 2002. The spacecraft appeared to have entered the termination shock region and about six months later, it re-entered a region of more normal solar wind conditions.

In that interval, the spacecraft traveled more than 400 million miles. ‘‘This is our first direct look at the incredibly dynamic activity in the solar system’s outer limits,’’ Krimigis said. A group headed by Dr Frank B. McDonald of the University of Maryland concluded from strength and behaviour of high-energy particles and magnetic fields around Voyager 1 that the spacecraft may be in the neighbourhood of the critical boundary, but has yet to cross over. The lack of consensus did not seem to upset other scientists. They suggested that some of the theoretical models of conditions toward the edge of the solar system, far from the nine planets, may be flawed or oversimplified.

‘‘It means there’s something new to learn in this final frontier of the solar system,’’ Dr Edward C. Stone, the chief Voyager scientist and a physicist at the California Institute of Technology, said at the news conference. In a commentary in Nature, Dr Len A. Fisk, a space scientist at the University of Michigan who is not involved with the two research teams, said that he tended to agree that the ‘‘the termination shock has been crossed’’.

The two identical spacecraft, launched in 1977, explored the outer planets and are on course to be the first man-made objects to leave the solar system, wherever its outermost boundary.

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Barring breakdowns, the craft are expected to keep sending back messages until 2020, when the electric power will probably run out. (NYT)