TAG | NASA’s Voyager 2 spacecraft finds lopsided shape of solar system |
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| by William Atkins | |
| Sunday, 06 July 2008 | |
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Page 2 of 3 Launched from Earth on August 20, 1977, Voyager 2 is an interstellar probe—meaning: it will soon be one of the few spacecraft built by humans that will leave the confines of our solar system and enter "interstellar space." Interstellar space is defined as the region of space beyond the heliopause, or the boundary where the “solar wind” of the Sun can no longer hold back the “stellar winds” from relatively nearby stars. The data from Voyager 2 that the heliosphere is lopsided contains the most detailed information so far received about the characteristics of the edge of our solar system. It also tells scientists that the "termination shock" is cooler and moving faster than previously thought. The termination shock occurs when the solar wind, made of electrically charged particles, becomes so weak (the further distance from the Sun the solar wind goes, the weaker it becomes) that it cannot hold back the onrush of particles coming in from interstellar space. In essence, the termination shock is the outer boundary (end) of our solar system—the point where the influence of the Sun theoretically ends—and the beginning of interstellar space (all of space outside of the solar system). The data found by Voyager was published on Thursday, July 3, 2008, in a series of articles within the Journal Nature. The title page of the Nature issue is called “Leaving the Heliosphere.” The papers describe Voyager 2 entering the termination shock on August 31, 2007, at a distance of about 7.8 billion miles (12.6 billion kilometers). Voyager 1, also on a voyage to exit the solar system, passed through the termination shock in December 2004 at a point about ten billion miles away the point by which Voyager 2 passed through the termination shock. Voyager 1 passed the termination shock at about 8.7 billion miles from the Sun—nearly one billion miles further away from the Sun that Voyager 2 passed through the termination shock. U.S. astrophysicist Leonard Burlaga (NASA’s Goddard Space Flight Center) described astronomers previous view of the termination shock. Burlaga said, "We used to assume that it's all symmetric and simple.” Now we know it is not symmetric and simple. The Scientific American article “Voyager 2 Finds Lopsided Solar System” states that the solar wind, at this point, is no more than a “couple of protons and electrons per gallon.“ U.S. astrophysicist J.R. Jokipii (University of Arizona’s Lunar and Planetary Laboratory) comments on the ability of Earth astronomers to measure such few particles: "It's almost impossible to measure. You have to give it to these experimenters." Where does Voyager 2 go from here? Page three explains. |
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