THE BIG READ: The story of the furthest man-made object from Earth
In reaching this milestone, it has traversed more than 25bn kilometres of space, as it visited the planets (it actually shortened Jupiter’s year during its sling-shot manoeuvre around the gas giant, when it caused the planet to move closer to the sun).
Now, amid claims Voyager 1 has immersed itself in the void beyond the influence of the sun (see panel), Nasa scientists are still waiting for the day when the data confirms it has left the outer part of the heliosphere — a stagnation layer or cosmic doldrums, where the sun’s charged-particle wind measures zero.
But if Voyager is to be our emissary as it transcends the boundaries, one of its creators, project scientist Ed Stone, continues to be an equally-esteemed ambassador for space exploration.
He said that, while Voyager’s latest milestone was a long-shot as they started its five-year construction in 1972, it nevertheless was a lofty aspiration.
“We had hopes Voyager would reach this distance, but no one knew how far it would go. It must be remembered that Voyager was launched when the space age was just 20 years old. We were optimistic that, if we were lucky, it would keep going,” says the 77-year-old, who continues to teach at the California Institute of Technology (Caltech).
Most distant image of Earth, taken by Voyager 1. In 2013, how about remembering we're all on this dot together? http://t.co/5Dd45JkT
— Marcus Chown (@marcuschown) September 6, 2013
Voyager actually comprises twin probes, with Voyager 2, launched a fortnight before Voyager 1. It is not hyperbole to say that the pair’s odysseys amount to a unique, almost mind-blowing achievement, opening our eyes to our sibling planets and their often-exotic menagerie of moons.
Included among its discoveries were Jupiter’s dozensof interacting hurricane-like storms, erupting volcanoes on Jupiter’s moon Io, with its mottled, pepperoni-pizza-like surface, hints of an ocean beneath the cracked icy crust of Jupiter’s moon Europa, methane in the atmosphere of Saturn’s moon Titan, suggesting methane rain; Neptune’s 2,000 kilometre-per-hour (1,200mph) winds; geysers spouting from the polar cap on Neptune’s moon Triton, with its surface temperature of -198.8C (-390F) the coldest temperature of any body known in the solar system.
“When I look back, I realise how little we actually knew about the solar system before Voyager,” says Stone. “We discovered things we didn’t know were there to be discovered, time after time.”
With Voyager responsible for so many achievements, Stone demurred when asked to pick his highlight, before touching down on the volcanoes of Io.
“It’s been such a rich, mission, one that characterises human endeavour, but one that stands out is the discovery of eight active volcanoes on Io. Previously we only knew of volcanoes on Earth. It’s amazing to think that this small moon had 10 times more volcanic activity than on Earth and, above all, it confirmed for us the diversity of the solar system.”
It is worth, at this stage, to point out that the same year the Voyagers left terra firma, ABBA were top of the pops with ‘Knowing Me, Knowing You’, Star Wars was the top-grossing film in the US and Jack Lynch was settling into his second term as Taoiseach. It was also the year the space shuttle Enterprise test vehicle took its maiden flight after piggybacking on a Boeing 747.
Considering the time lapse then, it should not come as a surprise to find that Voyager’s computer memory could fit 125,000 times into an 8-gigabyte iPod. Looking back, Stone is glad that they opted to incorporate doubles of its three computers, as well as providing it with a nuclear power source.
“Several key thing have given Voyager a long life. Firstly, its power source, which comes from the decay of plutonium 238, a simple system that gives heat that is converted to power. The power decays just four watts a year. It is not much, but it adds up. This means we will be able to leave all the instruments on until 2020, but then will have to start turning them off one at a time, until 2025/26 when the power is expected to run out,” says Stone, who had an asteroid (5841) named after him in 1996.
Asked, on the other hand, if there was anything he regretted not incorporating in Voyager, he says: “Nothing comes to mind, it’s been so successful. We started designing it in 1972 and had five years. It’s hard to imagine we should or could have done anything more.”
Like a boy about to open a Christmas present, Stone is eager to see what lies in interstellar space.
“It will be a major milestone. The first man-made object to leave our solar bubble, it will become immersed in the material from the explosion of other stars. What we are trying to understand is how our sun interacts with what’s beyond. Inside, almost all the material is from the sun, outside it is from the explosions of supernovae with cosmic rays and we have no idea how it would affect human space flight.”
Signals sent from Earth take 17 hours to reach Voyager 1 travelling at the speed of light. The returning signal received on earth is 20bn times weaker than the power required to operate a modern-day electronic digital watch.
“Voyager has a 23-watt transmitter, and we pick up the signal on a set of three antennae,” says Stone. “One is outside Madrid, one is in the desert in California and one is near Canberra in Australia, so we can always listen as the Earth rotates. We manage to listen every day, but only for eight hours, as we have to monitor other missions.”
The Voyager duo may be renowned for their information-collecting achievements and majestic meanderings, but they are also renowned for their ‘golden records’. The Pioneer spacecraft 9 and 10 had small metal plaques identifying their time and place of origin. NASA went further with Voyager and asked astronomer Carl Sagan and a committee to distill the wonders of Earth and communicate it to extraterrestrials on a gold-coated copper disc.
It contains 115 images and a variety of natural sounds, such as those made by surf, thunder, whales and barking dogs. Included were the brainwaves of a young woman in love (a member of the recording team, Ann Druyan); music from different cultures and eras, including works by Mozart and Chuck Berry’s ‘Johnny B Goode’.
It also carries spoken greetings from people in 55 languages, beginning with Akkadian, which was spoken in Sumer — modern Iraq — about 6,000 years ago, and ending with Wu, a modern Chinese dialect. Then US president Jimmy Carter and UN secretary general Kurt Waldheim added printed messages. Each record is encased in a protective aluminum jacket, together with a cartridge and a needle. Instructions, in symbolic language, explain how the record is played.
It will be 40,000 years before Voyager makes a close approach to any other planetary system, but Sagan was not beyond venturing to infinity... and beyond: “A billion years from now, when everything on Earth we’ve ever made has crumbled into dust, when the continents have changed beyond recognition and our species is unimaginably altered or extinct, the Voyager record will speak for us.”
As for Stone, gold records aside, he is wary of declaring that sentient life exists outside Earth. “I think microbial life exists, but whether there is any intelligent life, I’m not so sure. Space is very empty.
“I believe instead that the disc is a message to all of us on Earth: That we had the ability to send a message, it is a milestone in human innovation.”
A claim by University of Maryland researchers that Voyager 1 has “at long last left our solar system and entered interstellar space” has been refuted by the Voyager chief scientist, Ed Stone.
The university’s Marc Swisdak, and fellow plasma physicists, James F Drake, and Merav Opher, of Boston University, constructed a model of the outer edge of the solar system, indicating Voyager 1 entered interstellar space on Jul 27, 2012, a finding counter to recent papers by NASA and other scientists.
While the university researchers and Stone concur that there has been a disappearance in the sun’s particle counts, corresponding with a large rise in galactic particle counts, they disagree about magnetism.
Stone says Voyager 1 will change direction when leaving the influence of the sun (a bubble called the heliosphere), but the university scientists propose that solar and interstellar magnetic field lines break and reconnect, creating “a complex set of nested magnetic islands”.
Stone told the Irish Examiner: “The paper from the University of Maryland is a theoretical model. It tries to explain the observations... in the context of the process of magnetic reconnection between the solar and interstellar magnetic field lines.
Changes in the charged particles are what their model predicts would happen when you cross over into interstellar space. A model like this cannot prove that Voyager 1 crossed into interstellar space.
“The Voyager team also thought, on first notice, that the charged particle data, from July and August 2012, could herald entry into interstellar space, but the magnetic field direction had not changed.
“We need to continue analysing our recent data. When that’s done, we’ll have a much better understanding of what the environment around Voyager 1 is like.”
Meanwhile, four half-hour, hands-on, family-friendly sessions on astronomy will be given at Blackrock Castle Observatory (BCO), Cork, tonight. It starts at 8pm and will be followed by a lecture on the mathematician, Alan Turing.
It is presented by Jean Lassègue, of the French National Centre for Scientific Research, while clear skies will permit the Cork Astronomy Club to train our eyes towards the constellations.
This artist’s concept shows NASA’s two Voyager spacecraft exploring a turbulent region of space known as the heliosheath, the outer shell of the bubble of charged particles around our sun.
On February 14, 1990, Nasa scientists instructed the cameras of Voyager 1 to point back and take a series of pictures of the sun and the planets to create the first “portrait” of our solar system as seen from the outside. In taking this mosaic, consisting of 60 frames, Voyager 1 made several images of the inner solar system, including Earth — the Pale Blue Dot — from a distance of approximately 4 billion miles. The sun is seen as the bright object in the centre of the circle of frames. The wide-angle image of the sun was taken with the camera’s darkest filter and the shortest possible exposure (5 thousandths of a second).
http://photojournal.jpl.nasa.gov/catalog/PIA00451
Voyager 2 was launched (above) on August 20, 1977, from the NASA Kennedy Space Center at Cape Canaveral in Florida, propelled into space on a Titan/Centaur rocket. A montage of images of the planets visited by Voyager 2, Jupiter, Saturn, Uranus and Neptune (top left), an enormous volcanic explosion on Jupiter’s moon Io captured by Voyager 2 (middle left) and Jupiter’s moon Io, with its mottled, pepperoni-pizza-like surface (bottom left).
A picture from Voyager 2 shows Neptune and its Great Dark Spot and its companion bright smudge; on the west limb the fast moving bright feature called Scooter and the little dark spot are visible (above) and Voyager 1’s image of Saturn and its ring taken in 1980 (below).
To accomplish their two-planet mission to Jupiter and Saturn, the Voyager spacecraft were built to last just five years.
Benefiting from a rare alignment of the outer planets — which occurs about every 175 years — each Voyager used the enormous gravitational power of Jupiter to be hurled on to Saturn, experiencing a sun-relative speed increase of about 35,700mph. Jupiter was initially slowed in its orbit around the sun by this manoeuvre, but by only the equivalent of one foot per trillion years.
However, because Jupiter had slowed it immediately began to fall slightly inward toward the sun, the net effect being that the Jupiter’s speed averaged over a Jovian year (11.8 Earth years) actually increased a tiny amount and the length of Jupiter’s year decreased a very tiny amount.
Gravity-assist slingshots followed at Saturn and Uranus for Voyager 2 to complete its Grand Tour flight to Neptune, reducing the trip time by almost 20 years when compared to an unassisted trip.
Each Voyager spacecraft comprises some five million parts. A colour TV contains about 2,500 equivalent parts, meaning each Voyager has the equivalent electronic circuit complexity of some 2,000 colour TVs.
The Voyager probes even have their own Twitter account: twitter.com/NASAVoyager
"Consider again that dot. That's here. That's home," as Sagan said. See the 2013 pale blue dot by @CassiniSaturn http://t.co/obM93P4iSf
— ARCHIVED - NASA Voyager (@NASAVoyager) July 24, 2013
The total cost of the Voyager mission from its inception in May 1972 through the Neptune encounter was $865m, equivalent to just 8 cents per US resident per year.
A total of five trillion bits of scientific data had been returned to Earth by both Voyager spacecraft at the completion of the Neptune encounter.
Imagine tacking the Irish Examiner to a tree... and walking one kilometre, turning and trying to read it. Well, the resolution of the Voyager television cameras is sharp enough to allow you do this.
The rings of Saturn appeared to the Voyagers as a dazzling necklace of 10,000 strands. Trillions of ice particles and house-sized bergs race along each of the million-kilometre-long tracks, with the traffic flow orchestrated by the combined gravitational tugs of Saturn, a retinue of moons and moonlets.
The rings of Saturn are so thin in proportion to their 171,000km (106,000 miles) width that, if a full-scale model were to be built with the thickness of an LP, the model would have to measure four miles from its inner edge to its outer rim.
The digital tape recorder aboard each Voyager recording scientific data should not begin to wear out until the tape has been moved back and forth a distance comparable to that of the width of the United States. It is akin to playing a two-hour video cassette once a day for 33 years without a failure.
Pele, the largest of the volcanoes seen on Jupiter’s moon Io, is throwing sulphur and sulphur-dioxide to heights 30 times that of Everest and the fallout zone covers an area the size of France.
Like the HAL computer in the sci-fi film 2001: A Space Odyssey, each Voyager is autonomous, with seven fault-protection routines. It can place itself in a safe state in a matter of seconds, which is critical for its survival when round-trip communication times for Earth stretch, at this stage, to 34 hours.
In about 40,000 years, Voyager 1 will drift within 1.6 light years (9.3 trillion miles) of AC+79 3888, a star in the constellation of Camelopardalis. In some 296,000 years, Voyager 2 will pass 4.3 light years (25 trillion miles) from Sirius, the brightest star in the sky.
A total of 11,000 work-years was devoted to the Voyager project through the Neptune encounter in 1989.
A set of small thrusters provides Voyager with the capability for attitude control and trajectory correction.
Each has a thrust of only three ounces. In the absence of friction, on a level road, it would take nearly six hours to accelerate a large car up to a speed of 48km/h (30mph) using one of the thrusters.
The Voyager magnetometers are mounted on a frail, spindly, fibreglass boom that was unfurled from a two-foot-long can shortly after the spacecraft left Earth.
The boom telescoped and rotated out of the cannister to an extension of nearly 13 metres (43ft).
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