On August 25th, 2012, the Voyager 1 spacecraft accomplished something no human-made object ever had before. After exploring the Uranus, Neptune, and the outer reaches of the Solar System, the spacecraft entered interstellar space. In so doing, it effectively became the most distant object from Earth and traveled further than anyone, or anything, in history.
Well, buckle up, because according to NASA mission scientists, the Voyager 2 spacecraft recently crossed the outer edge of the heliopause – the boundary between our Solar System and the interstellar medium – and has joined Voyager 1 in interstellar space. But unlike its sibling, the Voyager 2 spacecraft carries a working instrument that will provide the first-ever observations of the boundary that exists between the Solar System and interstellar space.
Forty years ago, the Voyager 1 and 2 missions began their journey from Earth to become the farthest-reaching missions in history. In the course of their missions, the two probes spent the next two decades sailing past the gas giants of Jupiter and Saturn. And while Voyager 1 then ventured into the outer Solar System, Voyager 2 swung by Uranus and Neptune, becoming the first and only probe in history to explore these worlds.
This summer, the probes will be marking the fortieth anniversary of their launch – on September 5th and August 20th, respectively. Despite having traveled for so long and reaching such considerable distances from Earth, the probes are still in contact with NASA and sending back valuable data. So in addition to being the most distant missions from Earth, they are the longest-running mission in history.
In addition to their distance and longevity, the Voyager spacecraft have also set numerous other records for robotic space missions. For example, in 2012, the Voyager 1 probe became the first and only spacecraft to have entered interstellar space. Voyage 2, meanwhile, is the only probe that has explored all four of the Solar System’s gas/ice giants – Jupiter, Saturn, Uranus and Neptune.
Their discoveries also include the first active volcanoes beyond Earth – on Jupiter’s moon Io – the first evidence of a possible subsurface ocean on Europa, the dense atmosphere around Titan (the only body beyond Earth with a dense, nitrogen-rich atmosphere), the craggy surface of Uranus’ “Frankenstein Moon” Miranda, and the ice plume geysers of Neptune’s largest moon, Triton.
These accomplishments have had immeasurable benefits for planetary science, astronomy and space exploration. They’ve also paved the way for future missions, such as the Galileo and Juno probes, the Cassini-Huygens mission, and the New Horizons spacecraft. As Thomas Zurbuchen, the associate administrator for NASA’s Science Mission Directorate (SMD), said in a recent press statement:
“I believe that few missions can ever match the achievements of the Voyager spacecraft during their four decades of exploration. They have educated us to the unknown wonders of the universe and truly inspired humanity to continue to explore our solar system and beyond.”
But what is perhaps most memorable about the Voyager missions is the special cargo they carry. Each spacecraft carries what is known as the Golden Record, a collection of sounds, pictures and messages that tell of Earth, human history and culture. These records were intended to serve as a sort of time capsule and/or message to any civilizations that retrieved them, should they ever be recovered.
As noted, both ships are still in contact with NASA and sending back mission data. The Voyager 1 probe, as of the writing of this article, is about 20.9 billion km (13 billion mi; 140 AU) from Earth. As it travels northward out of the plane of the planets and into interstellar space, the probe continues to send back information about cosmic rays – which are about four times as abundant in interstellar space than around Earth.
From this, researchers have learned that the heliosphere – the region that contains the Solar System’s planets and solar wind – acts as a sort of radiation shield. Much in the say that Earth’s magnetic field protects us from solar wind (which would otherwise strip away our atmosphere), the heliopause protects the Solar planets from atomic nuclei that travel at close to the speed of light.
Voyager 2, meanwhile, is currently about 17.7 billion km (11 billion mi; 114.3 AU) from Earth. It is traveling south out of the plane of the planets, and is expected to enter interstellar space in a few years. And much like Voyager 1, it is also studying how the heliosphere interacts with the surroundings interstellar medium, using a suite of instruments that measure charged particles, magnetic fields, radio waves and solar wind plasma.
Once Voyager 2 crosses into interstellar space, both probes will be able to sample the medium from two different locations simultaneously. This is expected to tell us much about the magnetic environment that encapsulates our system, and will perhaps teach us more about the history and formation of the Solar System. On top of that, it will let us know what kinds of hazards a possible interstellar mission will have to contend with.
The fact that the two probes are still active after all this time is nothing short of amazing. As Edward Stone – the David Morrisroe Professor of Physics at Caltech, the former VP and Director of NASA’s Jet Propulsion Laboratory, and the Voyager project scientist – said:
“None of us knew, when we launched 40 years ago, that anything would still be working, and continuing on this pioneering journey. The most exciting thing they find in the next five years is likely to be something that we didn’t know was out there to be discovered.”
Keeping the probes going has also been a challenge since the amount of power they generate decreases at a rate of about four watts per year. This has required that engineers learn how to operate the twin spacecraft with ever-decreasing amounts of power, which has forced them to consult documents that are decades old in order to understand the probes’ software and command functions.
Luckily, it has also given former NASA engineers who worked on the Voyager probes the opportunity to offer their experience and expertise. At present, the team that is operating the spacecraft estimate that the probes will run out of power by 2030. However, they will continue to drift along their trajectories long after they do so, traveling at a speed of 48,280 km per hour (30,000 mph) and covering a single AU every 126 days.
At this rate, they will be within spitting distance of the nearest star in about 40,000 years, and will have completed an orbit of the Milky Way within 225 million years. So its entirely possible that someday, the Golden Records will find their way to a species capable of understanding what they represent. Then again, they might find their way back to Earth someday, informing our distant, distant relatives about life in the 20th century.
And if the craft avoid any catastrophic collisions and can survive in the interstellar medium of space, it is likely that they will continue to be emissaries for humanity long after humanity is dead. It’s good to leave something behind!
A quarter of a century has passed since NASA’s Voyager 1 spacecraft snapped the iconic image of Earth known as the “Pale Blue Dot” that shows all of humanity as merely a tiny point of light.
The outward bound Voyager 1 space probe took the ‘pale blue dot’ image of Earth 25 years ago on Valentine’s Day, on Feb. 14, 1990 when it looked back from its unique perch beyond the orbit of Neptune to capture the first ever “portrait” of the solar system from its outer realms.
Voyager 1 was 4 billion miles from Earth, 40 astronomical units (AU) from the sun and about 32 degrees above the ecliptic at that moment.
The idea for the images came from the world famous astronomer Carl Sagan, who was a member of the Voyager imaging team at the time.
He head the idea of pointing the spacecraft back toward its home for a last look as a way to inspire humanity. And to do so before the imaging system was shut down permanently thereafter to repurpose the computer controlling it, save on energy consumption and extend the probes lifetime, because it was so far away from any celestial objects.
Sagan later published a well known and regarded book in 1994 titled “Pale Blue Dot,” that refers to the image of Earth in Voyagers series.
“Twenty-five years ago, Voyager 1 looked back toward Earth and saw a ‘pale blue dot,’ ” an image that continues to inspire wonderment about the spot we call home,” said Ed Stone, project scientist for the Voyager mission, based at the California Institute of Technology, Pasadena, in a statement.
Six of the Solar System’s nine known planets at the time were imaged, including Venus, Earth, Jupiter, and Saturn, Uranus, Neptune. The other three didn’t make it in. Mercury was too close to the sun, Mars had too little sunlight and little Pluto was too dim.
Voyager snapped a series of images with its wide angle and narrow angle cameras. Altogether 60 images from the wide angle camera were compiled into the first “solar system mosaic.”
Voyager 1 was launched in 1977 from Cape Canaveral Air Force Station in Florida as part of a twin probe series with Voyager 2. They successfully conducted up close flyby observations of the gas giant outer planets including Jupiter, Saturn, Uranus and Neptune in the 1970s and 1980s.
Both probes still operate today as part of the Voyager Interstellar Mission.
“After taking these images in 1990, we began our interstellar mission. We had no idea how long the spacecraft would last,” Stone said.
Hurtling along at a distance of 130 astronomical units from the sun, Voyager 1 is the farthest human-made object from Earth.
Voyager 1 still operates today as the first human made instrument to reach interstellar space and continues to forge new frontiers outwards to the unexplored cosmos where no human or robotic emissary as gone before.
Here’s what Sagan wrote in his “Pale Blue Dot” book:
“That’s here. That’s home. That’s us. On it everyone you love, everyone you know, everyone you ever heard of, every human being who ever was, lived out their lives. … There is perhaps no better demonstration of the folly of human conceits than this distant image of our tiny world.”
Stay tuned here for Ken’s continuing Earth and planetary science and human spaceflight news.