by HARVEY LEIFERT
“Voyager 1 is the most remote human-made object,” Stone says. “It’s now 115 astronomical units from Earth,” that is, 115 times farther than Earth is from the sun, or “a bit more than 10 billion miles [16 billion kilometers].” Voyager 2 has traveled somewhat slower and in a different direction and is now around 14 billion kilometers from Earth.
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In the past six months, Voyager 1 has signaled that the radial speed of the solar wind is zero, meaning that the spacecraft is approaching the final boundary of the solar system, the heliopause. Stone and his colleagues had not expected Voyager to reach this point for several more years, meaning that the boundary lies closer to the sun than they had thought. “So, our models need to be refined in order to account for these new observations, and that will tell us, once that’s done, how much farther Voyager has to go” before it enters interstellar space. Several presentations at the American Geophysical Union’s Fall Meeting in San Francisco this week deal with these issues, he said.
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