Nancy Neal/Bill Steigerwald<br />Goddard Space Flight Center, Greenbelt, Md. Nov. 5, 2003<br />(Phone: 301/286-0039/8955)<br /><br /><br />Carolina Carnalla-Martinez<br />Jet Propulsion Laboratory , Pasadena, Calif.<br />(Phone: 818/354-9382)<br /><br /><br />RELEASE: 03-354<br /><br /><br />VOYAGER APPROACHING SOLAR SYSTEM'S FINAL FRONTIER<br /><br /><br /> NASA's Voyager 1 spacecraft is about to make history <br />again. It is the first spacecraft to enter the solar system's <br />final frontier, a vast expanse where wind from the sun blows <br />hot against thin gas between the stars: interstellar space.<br /><br /><br />However, before it reaches this region, Voyager 1 must pass <br />through the termination shock, a violent zone that is the <br />source of beams of high-energy particles. Voyager's journey <br />through this turbulent zone will give scientists the first <br />direct measurements of our solar system's unexplored final <br />frontier, the heliosheath. Scientists are debating if this <br />passage has already begun. Two papers about this research are <br />being published in Nature today.<br /><br /><br />The first paper, by Dr. Stamatios Krimigis of the Johns <br />Hopkins University Applied Physics Laboratory, Laurel, Md., <br />and his team, supports the claim Voyager 1 passed beyond the <br />termination shock. The second paper, by Dr. Frank McDonald of <br />the University of Maryland, College Park, Md., and his team, <br />disputes the claim. A third paper, published October 30 in <br />Geophysical Research Letters by GSFC's Dr. Leonard Burlaga, <br />and collaborators, states Voyager 1 did not pass beyond the <br />termination shock.<br /><br /><br />"Voyager 1 has seen striking signs of the region deep in <br />space where a giant shock wave forms, as the wind from the <br />sun abruptly slows and presses outward against the <br />interstellar wind. The observations surprised and puzzled us, <br />so there is much to be discovered as it begins exploring this <br />new region at the outer edge of the solar system," said Dr. <br />Edward Stone, Voyager Project Scientist, California Institute <br />of Technology, Pasadena, Calif.<br /><br /><br />Launched on September 5, 1977, Voyager explored the giant <br />planets Jupiter and Saturn before being tossed out toward <br />deep space by Saturn's gravity. It is approaching, and may <br />have temporarily entered, the region beyond termination <br />shock. At more than eight billion miles from the sun, Voyager <br />1 is the most distant object from Earth built by humanity.<br /><br /><br />The termination shock is where the solar wind, a thin stream <br />of electrically charged gas blown constantly from the sun, is <br />slowed by pressure from gas between the stars. At the <br />termination shock, the solar wind slows abruptly from its <br />average speed of 700,000 to 1,500,000 mph.<br /><br /><br />Estimating the location of the termination shock is hard, <br />because we don't know the precise conditions in interstellar <br />space. We do know speed and pressure of the solar wind <br />changes, which causes the termination shock to expand, <br />contract and ripple.<br /> <br />>From about August 1, 2002, to February 5, 2003, scientists <br />noticed unusual readings from the two energetic-particle <br />instruments on Voyager 1, indicating it had entered a region <br />of the solar system unlike any previously encountered. This <br />led some to claim Voyager 1 may have entered a transitory <br />feature of the termination shock. <br /><br /><br />The controversy would be resolved if Voyager could measure <br />the speed of the solar wind, because the solar wind slows <br />abruptly at the termination shock. However, the instrument <br />that measured solar wind speed no longer functions on the <br />venerable spacecraft. Scientists must use data from <br />instruments still working to infer if Voyager pierced the <br />termination shock.<br /><br /><br />"We have used an indirect technique to show the solar wind <br />slowed down from about 700,000 mph to much less than 100,000 <br />mph. We used this same technique when the instrument <br />measuring the solar wind speed was still working. The <br />agreement between the two measurements was better than 20 <br />percent in most cases," Krimigis said.<br /><br /><br />"The analysis of the Voyager 1 magnetic field observations in <br />late 2002 indicate that it did not enter a new region of the <br />distant heliosphere by having crossed the termination shock. <br />Rather, the magnetic field data had the characteristics to be <br />expected based upon many years of previous observations, <br />although the intensity of energetic particles observed is <br />unusually high," Burlaga said.<br /><br /><br />The Voyager spacecraft were built and are operated by JPL. <br />The Voyagers were equipped with three radioisotope <br />thermoelectric generators to produce electrical power for the <br />spacecrafts' systems and instruments. Steadily operating for <br />26 years, the Voyagers owe their longevity to these <br />generators, which produce electricity from the heat generated <br />by the natural decay of plutonium dioxide. For images, <br />animation and the complete press release on the Internet, <br />visit:<br /><br /><br />http://www.gsfc.nasa.gov/topstory/2003/1105voyager.html