For the second time in history, a human-made object has reached the space between the stars. NASA’s Voyager 2 probe now has exited the heliosphere – the protective bubble of particles and magnetic fields created by the Sun.
Voyager 2 launched in 1977, 16 days before Voyager 1, and both have traveled well beyond their original destinations. The spacecraft were built to last five years and conduct close-up studies of Jupiter and Saturn. However, as the mission continued, additional flybys of the two outermost giant planets, Uranus and Neptune, proved possible.
As the spacecraft flew across the solar system, remote-control reprogramming was used to endow the Voyagers with greater capabilities than they possessed when they left Earth. Their two-planet mission became a four-planet mission. Their five-year lifespans have stretched to 41 years, making Voyager 2 NASA’s longest running mission.
By comparing data from different instruments aboard the trailblazing spacecraft, mission scientists determined the probe crossed the outer edge of the heliosphere on Nov. 5. This boundary, called the heliopause, is where the tenuous, hot solar wind meets the cold, dense interstellar medium. Its twin, Voyager 1, crossed this boundary in 2012, but Voyager 2 carries a working instrument that will provide first-of-its-kind observations of the nature of this gateway into interstellar space.
Voyager 2 now is slightly more than 11 billion miles (18 billion kilometers) from Earth. Mission operators still can communicate with Voyager 2 as it enters this new phase of its journey, but information – moving at the speed of light – takes about 16.5 hours to travel from the spacecraft to Earth. By comparison, light traveling from the Sun takes about eight minutes to reach Earth. The PLS aboard Voyager 2 observed a steep decline in the speed of the solar wind particles on Nov. 5. Since that date, the plasma instrument has observed no solar wind flow in the environment around Voyager 2, which makes mission scientists confident the probe has left the heliosphere.
In addition to the plasma data, Voyager’s science team members have seen evidence from three other onboard instruments – the cosmic ray subsystem, the low energy charged particle instrument and the magnetometer – that is consistent with the conclusion that Voyager 2 has crossed the heliopause.
Voyager’s team members are eager to continue to study the data from these other onboard instruments to get a clearer picture of the environment through which Voyager 2 is traveling. “There is still a lot to learn about the region of interstellar space immediately beyond the heliopause,” said Ed Stone, Voyager project scientist based at Caltech in Pasadena, California.
The Voyager Interstellar Mission is a part of NASA’s Heliophysics System Observatory, sponsored by the Heliophysics Division of NASA’s Science Mission Directorate in Washington.
For more information about the Voyager mission, visit: https://www.nasa.gov/voyager