LOS ANGELES — NASA's long-running Voyager 1 spacecraft is barreling its way toward the edge of the solar system.
NASA said Monday that recent readings show the average outward speed of the solar wind has slowed to zero, meaning the spacecraft is nearing ever closer to the solar system's edge to a boundary known as the heliopause. "It's telling us the heliopause is not too far ahead," said project scientist Edward Stone of the NASA Jet Propulsion Laboratory.
"We knew this was going to happen. The question was when," Stone said. The Voyager results will be presented Tuesday at the American Geophysical Union meeting in San Francisco.Launched in 1977, the nuclear-powered Voyager 1 and its twin Voyager 2 toured Jupiter, Saturn, Uranus and Neptune, then kept going in different directions. Voyager 1 veered north while Voyager 2 headed south. Hurtling at 38,000 mph (61,150 kph), Voyager 1 is 10.8 billion miles (17.3 billion kilometers) from the sun. Voyager 2 is traveling slower at 35,000 mph (56,300 kph) and is 8.8 billion miles (14.1 billion kilometers) from the sun.
When Voyager 1 finally leaves the solar system, scientists expect to see a telltale change in the wind. Interstellar wind is slower, colder and denser than solar wind.