For more than a year, some members of the scientific community had been arguing that based on Voyager’s speed and predicted trajectory, it likely achieved this remarkable feat last summer. And on several occasions NASA itself has announced that the spacecraft has come tantalizingly close to doing so, only to pull back, most recently in June of this year when they said it might still take years for the probe to reach the denser, particle-rich region of space that lies outside the heliosphere, the magnetic bubble that surrounds the Sun’s magnetic field. As it turns out, the space agency wasn’t playing coy, it was simply waiting for confirmation of Voyager’s passing of a series of scientific benchmarks.
Last summer, as expected, NASA detected changes in the concentration of particles surrounding the spacecraft, indicating that it had entered the interstellar region. The next tip-off was expected to a dramatic shift in the direction of the galaxy’s magnetic field past the boundaries of the heliosphere, but Voyager sent back no data indicated any significant change, causing confusion among the mission team. They now believe that the magnetic fields within and outside our solar system actually function and position themselves the same. This left a third test to determine the spacecraft’s true location, the relative density and large number of other highly charged particles emitted from the sun, known as plasma.
Hampering NASA’s efforts, the instruments designed to measure the plasma levels broke down in the 1980s, forcing scientists to improve by taking readings from an external antennae instead. But they received a lucky break when the after effects of a March 2012 sun burst (or coronal mass ejection) finally reached Voyager’s position in April of this year, providing new readings on the density of the plasma immediately surrounding the spacecraft, which turned out to be more than 40 times higher than that contained in the sun burst—and in the heliosphere itself. Digging back into earlier data sent back from Voyager, NASA discovered two other bumps, or oscillations, in the plasma density levels surrounding Voyager, confirming at last that the probe had passed into an entirely new region of interstellar space, sometime around August 25, 2012.
Despite NASA’s announcement of the landmark achievement, some scientists urge caution when discussing whether Voyager has technically left the solar system. In the strictest sense, the term solar system includes almost unfathomably distant comets that orbit the sun in a region known as the Oort cloud, some so far away that it would take Voyager more than 30,000 years to reach them. And while scientists predict that Voyager’s physical components (roughly 65,000 individual parts including an eight-track digital recorder) will continue its journey through space for millions of years, its scientific equipment has a much shorter shelf life. It expects to turn off its instruments within the next 20 years.
To conserve energy, Voyager 1’s cameras were turned off in 1980, only to be turned on again a decade later as the spacecraft began its approach to deepest space. It sent one final batch of 60 photos back to NASA on Valentine’s Day 1990, including a “family portrait” of our solar system, including the sun and several planets. Nearly four decades after its launch, Voyager 1, which NASA officials referred to as the “little spacecraft that could,” continues to send back scientific data utilizing a 23-watt transmitter no more powerful than a refrigerator light bulb. In fact, the spacecraft’s three interconnected computer systems contain less than 1 MB of memory combined, remarkable in an era where the simplest of smartphones has nearly 10 times as much. It takes roughly 16 hours for signals to from the probe to reach Earth, and vice versa.
Launched in the summer of 1977, the initial Voyager missions were designed to give scientists their first glimpses of the outer planets; Jupiter Saturn, Uranus and Neptune. Voyager 2, which was actually the first to depart, traveled a different route than its sister ship, and to date has covered more than 9.5 billion miles and is expected to make its way into interstellar space within the next few years. Both ships are identical (weighing approximately 1,500 pounds) and carry specially recorded messages etched on 12-inch gold-plated copper phonograph records—should they encounter any other life forms on their trek along the cosmic highway. Curated by the late astronomer Carl Sagan, they include a cultural timeline of life on Earth, including music and sound files, images and spoken greetings in more than 50 languages.