In August 1977 NASA sent a probe called Voyager 2 into space. And following its launch, the craft traveled to several planets in our solar system, sending back pictures and information on the celestial bodies to Earth. Yet all these years later, Voyager 2 is still active – and it’s been pushing the boundaries of what’s possible even further.
You see, in October 2018 NASA published a news release announcing that Voyager 2 may be approaching interstellar space. And this feat would certainly be momentous; if the craft managed to travel into this remote part of the galaxy, it would become only the second man-made entity to do so. The first craft to have reached this milestone had actually been the probe’s sister, Voyager 1, which had achieved the feat in 2013.
Then in December 2018 NASA confirmed that Voyager 2 had indeed made it into interstellar space. And even though Voyager 1 had already paved the way, this new development was still significant. Thanks to a certain functional instrument on board Voyager 2, NASA could now look forward to learning yet more about the universe.
But before we turn our attention to Voyager 2’s latest mission, let’s first consider what interstellar space actually is. The term “interstellar” literally means “between stars,” and that’s precisely where this section of the galaxy lies. However, it’s easier to discern the exact nature of interstellar space when contrasting it with what lies over the border.
Yes, as interstellar space is said to be different to the stretch of universe found within the vicinity of the Sun, it follows that there must be a sort of boundary positioned between these two separate regions. And, in fact, these two areas are indeed separated by a border – one known as the heliopause.
The heliopause is located in between interstellar space and an area known as the heliosphere – a large bubble of sorts that emanates from and encloses the Sun. And the heliosphere itself exists as a result of solar winds originating from the hot star that gives Earth its light.
One way to distinguish between the heliosphere and interstellar space is to look at the nature of the solar particles found in each region. Within the heliosphere, these tiny bits of matter are high in temperature and are dispersed quite widely; beyond the bubble, however, the particles are cooler and more tightly packed together.
For their part, both Voyager 1 and Voyager 2 have managed to cross past the outer edges of the heliosphere – and thus into interstellar space. Yet reaching this section of the galaxy wasn’t the main objective given to either craft, as they had initially been sent into the skies for other purposes.
As the probes’ names suggest, both were launched as part of NASA’s Voyager program. Voyager 2 was the first to be sent off on August 20, 1977, with its sister following suit on September 5 that year. And broadly speaking, the two craft were tasked with exploring the outer reaches of our solar system.
The pair of probes were designed in precisely the same manner, too, and are indistinguishable to look at. They also each apparently weigh 1,704 pounds, of which 231 pounds can be attributed to a range of scientific implements. And stowed away on both Voyager 1 and Voyager 2 is something known as the Voyager Golden Record.
The Voyager Golden Record is a phonograph record that carries sounds and a number of images from Earth. A committee led by famed astronomer Carl Sagan chose the discs’ contents, with the panel ultimately picking noises from nature as well as some musical pieces from various cultures on Earth.
And the music on the record was selected to exhibit a wide range of human tastes – taking in classical compositions by Bach and Beethoven along with some examples of pop. In fact, the addition of Chuck Berry’s “Johnny B. Goode” was apparently a cause for disquiet to some, who labeled the tune “adolescent.” However, Sagan apparently coolly responded to these concerns by saying, “There are a lot of adolescents on the planet.”
Then a copy of the Voyager Golden Record was sent aboard each of the two spacecraft in the unlikely event of their discovery by aliens. Speaking of the artifact to NASA in 1977, Sagan explained, “The spacecraft will be encountered and the record played only if there are advanced spacefaring civilizations in interstellar space. But… the launching of this bottle into the cosmic ocean says something very hopeful about life on this planet.”
Also included within the Voyager Golden Record are some 115 illustrations and photographs. A number of these present various mathematical and scientific theories, while others simply show more day-to-day aspects of human existence. In addition, there are a couple of notes included with each copy of the record, including one from then-president Jimmy Carter.
“This is a present from a small, distant world,” President Carter wrote to the potential discoverers of either probe. “[It is] a token of our sounds, our science, our images, our music, our thoughts and our feelings. We are attempting to survive our time so we may live into yours.”
Yet the Voyager mission was designed for more than just the potential for alien contact. Specifically, the two probes had initially been sent into space in order to investigate the planetary systems of Saturn and Jupiter. The craft managed to go even further than this, however, upon completion of these principal objectives.
Yes, after Voyager 2 had reached and analyzed Saturn and Jupiter, it continued on to Uranus and Neptune. The probe then visited Uranus’ planetary system in 1986 and Neptune’s in 1989. And to this very day, Voyager 2 remains the only spacecraft to have ever explored these two planets.
Voyager 1, meanwhile, became the third ever man-made entity to reach the speed necessary to leave the solar system. Even today, only five probes have achieved such a feat: the two Voyager spacecraft, Pioneer 10, Pioneer 11 and New Horizons. This last probe was sent to space in 2006, while the other four were launched throughout the 1970s.
And throughout the earlier years of the Voyager mission, the two spacecraft uncovered significant information regarding the planets in the outer solar system: Jupiter, Saturn, Uranus and Neptune. Using an array of scientific implements and cameras, the Voyager probes were able to make enlightening observations about these celestial bodies.
In January 1979 Voyager 1 started to photograph Jupiter, with the best images – snapped in March that year – able to show us more of the planet’s rings, magnetic fields and moons. And, intriguingly, volcanic activity was also recorded on the moon Io – thus marking the first time that such a phenomenon had been observed beyond Earth.
During its own journey flying past Jupiter in July 1979, Voyager 2 backed up its sister probe’s observations on Io’s volcano. In addition, the craft observed the Great Red Spot – the site of the biggest anticyclonic storm in our solar system. Estimates vary, but experts believe that the storm may have been raging for up to 350 years.
Then, following their respective flybys of Jupiter, the space probes both traveled to Saturn. Voyager 1 approached nearest the planet in November 1980, while Voyager 2 got closest in August 1981. And as had been the case with the Jupiter trips, the spacecraft revealed new details about Saturn through the data that they had acquired.
Voyager 1, for instance, photographed and noted some complicated features in Saturn’s rings. And while a failing piece of equipment compromised the integrity of these images, Voyager 2 was thankfully able to later snap higher-quality photos that in turn led to the discovery of numerous new details.
Both space probes also studied Saturn’s atmosphere, with Voyager 1 noting that this consisted predominately of helium and hydrogen. The pair additionally rotated around Saturn to discover the length of a day on the planet, which turned out to be nearly 11 Earth hours.
And Voyager 1’s course also involved drifting past Titan – Saturn’s biggest natural satellite and the second most sizeable in the solar system behind the Jupiter-orbiting Ganymede. What’s more, Titan is not only around 50 percent larger than our own Moon, but it’s actually bigger than the planet Mercury.
Experts were keen to observe Titan, too, meaning Voyager 2’s course would have been adjusted to complete the task if Voyager 1 couldn’t manage it. And this was despite the fact that such a diversion would have prevented Voyager 2 from ever making it to Uranus and Neptune.
Thankfully, Voyager 1 managed to observe Titan, thereby allowing Voyager 2 to travel on to Uranus. Then Voyager 1 journeyed towards the edge of the solar system, snapping images as it did so. One famous photograph from 1990 became the first “family portrait” of the solar system, showing what it looked like from the outside – with Earth as a dot in the distance.
Then in 1998 Voyager 1 overtook the Pioneer 10 space probe as the furthest man-made object from Earth. Apparently, Voyager 1 moves by 325 million miles every 12 months – or a single light year every 18,000 years. And in August 2012 it became the first craft to have ever reached interstellar space, too.
Voyager 2, meanwhile, reached its closest point to Uranus in January 1986. And during its time within the planet’s vicinity, it identified 11 formerly undiscovered moons. Voyager 2’s observations established, furthermore, that a day on Uranus lasts for just over 17 Earth hours.
Then in 1989 Voyager 2 managed to travel and get close to the planet of Neptune. And while there, the craft flew past Triton as well as six other moons that had hitherto gone unrecognized. The probe also discovered two rings that wrap around the dense ice giant.
Finally, after Voyager 2 had completed its flyby of Neptune, the planetary phases of its mission came to an end. But the craft wouldn’t be coming back to Earth. Instead, NASA decided to utilize the probe in order to learn more about the area outside the heliosphere. Yes, like its sister, Voyager 2 would be making its way to interstellar space.
And in December 2018 NASA revealed that Voyager 2 had passed through the heliosphere the month previously. How could the agency confidently make this claim? Well, it’s all down to a piece of equipment on Voyager 2 called a Plasma Science instrument, or PLS.
Yes, while the PLS hasn’t functioned on Voyager 1 since 1980, it works well on Voyager 2. For its part, the device is used to note the nature of solar wind particles within the heliosphere. And given that no solar wind has been detected around Voyager 2 since November 2018, this in turn proves the craft has now made it into interstellar space.
Furthermore, Voyager 2’s working PLS could be a boon for exploring the universe, as one expert on the device has suggested. John Richardson of the Massachusetts Institute of Technology told NASA in December 2018, “Even though Voyager 1 crossed the heliopause in 2012, it did so at a different place and a different time [to Voyager 2] and without the PLS data. So we’re still seeing things that no one has seen before.”
Information is now being sent back to Earth from both Voyager 1 and Voyager 2. And using the resulting data, NASA can examine the heliosphere and its response to factors from beyond its boundaries. This process is vital to making new discoveries, too, as the director of NASA’s heliophysics division has claimed.
“Voyager has a very special place for us in our heliophysics fleet,” NASA’s Nicola Fox has explained. “Our studies start at the Sun and extend out to everything the solar wind touches. To have the Voyagers sending back information about the edge of the Sun’s influence gives us an unprecedented glimpse of truly uncharted territory.”
It has been estimated that both Voyager 1 and Voyager 2 are capable of remaining functional until 2025. From that point on, the two may lose their electricity – thus putting an end to their scientific operations. Yet even if this is the case, the craft will have each endured for almost half a century after the beginning of their respective missions.
In fact, NASA initially sent the Voyager probes to space in 1977 with the intention of them working for five years. But their objectives to observe Jupiter and Saturn have long been completed, as have their observations of Uranus and Neptune. And now the spacecraft have even made it to interstellar space.
“I think we’re all happy and relieved that the Voyager probes have both operated long enough to make it past this milestone,” mission project manager Suzanne Dodd told the agency. She continued, “This is what we’ve all been waiting for. Now we’re looking forward to what we’ll be able to learn from having both probes outside the heliopause.”
Now, NASA is planning a new mission to build upon the pioneering work already undertaken by the Voyager probes. Currently, the so-called Interstellar Mapping and Acceleration Probe is scheduled to be launched in 2024. And who knows what new findings it may uncover to add to the data from the Voyager missions?