Reports from various news agencies today have been stating NASA’s Voyager-1 spacecraft as having left the solar system. Although some in the astronomy community feel that Voyager 1 is in fact now traversing interstellar space, NASA and officials at the agency’s Jet Propulsion Laboratory in California, the same folks who built the spacecraft and continue to operate and communicate with it to this day, stress that Voyager-1 is still in the solar system.
The following statement by Edward Stone, Voyager project scientist based at the California Institute of Technology, was released by NASA’s Jet Propulsion Laboratory this afternoon in response to the initial reports:
“It is the consensus of the Voyager science team that Voyager 1 has not yet left the solar system or reached interstellar space. In December 2012, the Voyager science team reported that Voyager 1 is within a new region called ‘the magnetic highway’ where energetic particles changed dramatically. A change in the direction of the magnetic field is the last critical indicator of reaching interstellar space and that change of direction has not yet been observed.”
The spacecraft, which launched from Florida’s Cape Canaveral Air Force Station in 1977, has travelled farther than any man-made object in history. Recent data sent from the spacecraft late last year show it is now pushing through a previously unknown region at the very edge of our known solar system, a “magnetic highway” that scientists feel is the final region before crossing into deep space.
This “new region” at the edge of our known solar system is where the sun’s magnetic field lines connect with the magnetic field lines of interstellar space, referred to by NASA as the “magnetic highway”. Low-energy charged particles from our solar bubble, known as the heliosphere, zoom out and allow higher-energy particles from interstellar space to zoom in. Before entering this region, the particles would zip around in all directions, but particles from deep space are now streaming over Voyager 1 regularly, something that has not been seen consistently before.
This data alone does not suggest Voyager 1 has reached interstellar space, because the direction of the sun’s magnetic field lines has not yet changed, but the data does show the region Voyager 1 is traveling through is rapidly changing. The influence of the sun is steadily weakening, while the influence from interstellar space is growing stronger.
“Although Voyager 1 still is inside the sun’s environment, we now can taste what it’s like on the outside because the particles are zipping in and out on this magnetic highway,” said Stone in late 2012. “We believe this is the last leg of our journey to interstellar space. Our best guess is it’s likely just a few months to a couple years away. The new region isn’t what we expected, but we’ve come to expect the unexpected from Voyager.”
“If we were judging by the charged particle data alone, I would have thought we were outside the heliosphere,” said Stamatios Krimigis, principal investigator of the low-energy charged particle instrument, based at the Johns Hopkins Applied Physics Laboratory, Laurel, Md. ”But we need to look at what all the instruments are telling us and only time will tell whether our interpretations about this frontier are correct.”
The spacecraft is currently speeding through the cosmos at over 38,000 miles-per-hour, and is currently over 18 billion miles away from Earth. The distances Voyager 1 has covered are so vast that astronomers do not actually measure them in miles, but in Astronomical Units, or AU. One AU is the average distance between the Earth and Sun, about 93 million miles. Voyager 1 is currently over 123 AU from Earth, or 123 times further from Earth than Earth is from the Sun, and clearing over 3 AU every Earth year (365 days). At these distances, radio signals from Voyager 1 take over seventeen hours to reach researchers here on Earth, and the round-trip light time from the sun is over thirty-four hours.
In December of 2004 Voyager 1 crossed through an area known as the “termination shock”, which marked the beginning of its voyage through the solar system’s heliosheath. The heliosheath is the outer boundary of our solar system still dominated by the sun’s magnetic field and particles contained in the solar wind. Although astronomers don’t know exactly just how wide the heliosheath is, and therefore cannot pinpoint exactly where the border between our solar system and interplanetary space is, they can see changes in the environment become more dramatic as Voyager 1 approaches the border, known as the heliopause.
In the nine years since Voyager 1 began its push through the heliosheath, the spacecraft has encountered several dramatic changes in its space environment—all pointing to its inevitable departure from our solar system into interstellar space. The amount of cosmic rays hitting the spacecraft continues to climb, and instruments on the spacecraft detected the supersonic solar wind dropped from 150,000 mph to zero as of last spring—held back from further expansion by the interstellar wind. Energetic particles from the solar system hitting the spacecraft have declined by nearly 50 percent over the last year, while the detection of high-energy electrons from interstellar space has increased 100 fold.
“We are in a magnetic region unlike any we’ve been in before—about 10 times more intense than before the termination shock—but the magnetic field data show no indication we’re in interstellar space,” said Leonard Burlaga, a Voyager magnetometer team member based at NASA’s Goddard Space Flight Center in Greenbelt, Md. “The magnetic field data turned out to be the key to pinpointing when we crossed the termination shock. And we expect these data will tell us when we first reach interstellar space.”
Although Voyager 1 is still in an environment dominated by the sun’s magnetic field, researchers expect to see the spacecraft exit the heliosphere sometime between now and 2015. When that occurs, big changes are expected to be seen in the data sent back to Earth. For example, energetic particles from the sun will be few and far between, and the magnetic field around Voyager 1 will change direction from that of the sun’s magnetic field to that of the unexplored magnetism of interstellar space.
Although traveling slower, and thus lagging behind its cousin Voyager 1, Voyager 2 is currently traversing the solar system on a course which will eventually see it leave the solar system as well. Both spacecraft are reported to be in good health, and have enough power and thruster fuel to operate until at least 2020, possibly until 2025.
“When the Voyagers launched in 1977, the Space Age was all of 20 years old,” said Stone. “Many of us on the team dreamed of reaching interstellar space, but we really had no way of knowing how long a journey it would be — or if these two vehicles that we invested so much time and energy in would operate long enough to reach it. This is very exciting. We are approaching the solar system’s final frontier.”