Posted: Thu, Nov 6, 2003, 7:38 AM ET (1238 GMT)
NASA's Voyager 1 spacecraft, launched over 25 years ago, may have reached the boundary between the solar system and interstellar space, although scientists are not in agreement about the claim. In one paper published in Thursday's issue of the journal Nature, a team of scientists led by Stamatios Krimigis of the Johns Hopkins University Applied Physics Laboratory argued that between August 2002 and February 2003 Voyager 1 may have reached the "termination shock", a turbulent region where the solar wind abruptly slows from 1-2 million kmph to a fraction of that speed. Voyager 1 is currently about 90 astronomical units, or 13.5 billion kilometers, from the Sun. The solar wind velocity measurement was made indirectly since the spacecraft's instrument that directly measures the speed no longer functions. Another paper by Frank McDonald of the University of Maryland, also published in Nature, as well as a third paper published last month in Geophysical Research Letters, dispute the claim, saying that the unusual magnetic field variations noted by the first group had characteristics seen in past years. The other papers do note, though, that the more recent observations have a much higher intensity of charged particles. Project officials hope that Voyager 2, whose instruments are in better condition, might be able to better measure the location of the termination shock once it reaches it.

Related Links:

•  NASA press release
•  SPACE.com article
•  New York Times article
•  Washington Post article
•  New Scientist article