Press Release
Voyager 1 Approaches Solar System鈥檚 Outer Limits
NASA Spacecraft Offers First Direct Look at Dynamic Region Before Interstellar Space
More than 25 years after leaving home, NASA鈥檚 spacecraft reached a key checkpoint on its historic journey toward interstellar space.
Analyzing six months of data from Voyager鈥檚 Low-Energy Charged Particle instrument, a team led by Dr. Stamatios Krimigis of The 秘密直播 University Applied Physics Laboratory (APL), Laurel, Md., determined that the spacecraft, while nearly 8 billion miles from Earth, passed through and later returned behind the turbulent zone known as the solar termination shock. At the termination shock, streams of electrically charged gas blown from the Sun 鈥 called the solar wind 鈥 slow down rapidly after colliding with gas and magnetic pressure from between the stars. The shock is also considered the last stop before the invisible boundary of the heliosphere, the bubble-like region of space under our Sun鈥檚 energetic influence.
鈥淰oyager 1 is giving us our first taste of interstellar space,鈥 says Krimigis, principal investigator for the Low-Energy Charged Particle (LECP) instrument, which was designed and built at APL. 鈥淭his is our first direct look at the incredibly dynamic activity in the solar system鈥檚 outer limits.鈥
Voyager 1 is the farthest manmade object in space, and from about Aug. 1, 2002 to Feb. 5, 2003, scientists noticed unusual readings from several instruments on the spacecraft indicating it had entered part of the solar system unlike any encountered before. Science team members鈥 views vary on what the data means; one instrument team maintains that Voyager approached, but didn鈥檛 cross, the termination shock. (Each team presents its views in the Nov. 6 issue of the journal .)
Krimigis says his team, however, found compelling evidence of a shock crossing in data from the LECP. The instrument, mounted on a motorized, rotating platform that allows it to scan the sky in all directions, determines the composition, charge and direction of certain energized particles as they zip through space.
First, the team noticed a hundred-fold increase in the intensity of these charged particles, and that they were streaming by the spacecraft mostly along the magnetic field perpendicular to Voyager鈥檚 path. 鈥淭his was remarkable,鈥 Krimigis says, 鈥渂ecause for 25 years, particles from the Sun were flowing straight out. We knew something strange must have happened to the solar wind that helps push these particles out.鈥
At a termination shock, the solar wind would brake abruptly from supersonic to subsonic speed. The instrument on Voyager 1 that could measure solar wind speed no longer operates; however, the LECP detector can measure it indirectly from the speed and direction of the ions riding with the solar wind. 鈥淭he solar wind had slowed from 700,000 miles per hour to less than 100,000 miles per hour,鈥 says Dr. Edmond Roelof, an LECP science team co-investigator at APL who developed analysis tools for just this type of data.
鈥淔lying a moving device on Voyager 鈥 in this case an electric motor 鈥 was considered a risk,鈥 says Dr. Robert Decker, an LECP science team co-investigator and the instrument project manager at the Applied Physics Laboratory. 鈥淏ut that rotating capability was key to collecting this data, and helping us figure out that the solar wind had virtually stopped.鈥