Voyager 1, the U.S. spacecraft that left our planet 35 years ago to explore Jupiter and Saturn and then kept going, has encountered a pocket of stillness at the edge of the solar system, a finding that surprised scientists.
At the rim of the heliosphere, a bubble of charged particles that surrounds the solar system, Voyager 1 has met with milder wind than scientists projected, according to a report published today in the journal Nature. Where scientists anticipated a shift in winds along the edge of the bubble, Voyager 1 data showed hardly a breeze or a waft, they said.
Hypotheses about solar wind at the bubble’s boundary may need to be reformulated, wrote the authors of the study, led by Robert Decker of the Applied Physics Laboratory at Johns Hopkins University in Laurel, Maryland. It’s a surprise and not completely understood, said Eric Christian, a NASA researcher who had been a project scientist with the Voyager mission.
“The wind has slowed to not quite a halt but almost,” said Ed Stone, a physics professor at the California Institute of Technology in Pasadena, in a telephone interview. “We must be getting closer to the edge of the bubble, but we can’t say how close.”
Voyager 1’s conditions are different from those surrounding its brother, Voyager 2, both launched by the National Aeronautics and Space Administration in 1977 and now traveling in opposite directions. Voyager 2, at about 14.9 billion kilometers (9.3 billion miles) from the Sun, is encountering the expected wind patterns, Stone said. He wasn’t an author on the study. Voyager 1 is about 18.2 billion kilometers from the Sun.
Whether it’s just in one region or what this means for how solar wind moves through the heliosphere is unknown, Stone said.
The two crafts have made discoveries such as erupting volcanoes on Jupiter’s moon Io, the hint of an ocean under the crust of its moon Europa and geysers spewing from Neptune’s moon Triton, according to NASA’s website.
They have enough power to operate until at least 2020, according to the Jet Propulsion Laboratory. At that point Voyager 2 is expected to be almost 17 billion kilometers from the Sun, and its brother, almost 20 billion.