Imagine that you're standing at the mouth of an infinitely deep well.
The very concept of "infinitely deep" is unfathomable to the human brain, but still, you want to explore the well's depths; you want to know what it's like down there. Normally, if the well was finite (ie it had a bottom filled with water), you'd simply toss a penny into it and count the seconds before you hear a "plop". Then, knowing the acceleration caused by gravity, you can do some quick math to calculate how deep the well is.
But this well is infinite. How would you deal with that? You still have a desire to learn what dragons lurk far below, but a dumb penny won't help you very much. What if you could strap that penny with a tiny microphone? That would be a start. Even better, a barometer would come in handy - at least then you can gain some measure of the atmospheric pressure as your penny drops deeper and deeper. What about a camera? Now we're talking! As the penny drops we can intermittently command our intelligent penny to take some snapshots of its mission as it falls deeper and deeper, imaging the alien environment deep inside this hypothetical well.
But what has this to do with a NASA space probe launched in 1977?
Like our fairy tale infinite well, Earth is the beginning of our fascination with the very real infinite cosmos that starts with mankind's natural drive to explore, and ends at the furthest most reaches of the Universe.
The Voyager missions were the beginning of our inquisitiveness to explore our cosmic backyard, but the twin space probes have now become something a lot more.
NASA launched our soon-to-be interstellar robotic explorers from the shores of Earth, equipped with cameras and sensors, intended to probe a very alien realm where our finite brains have little understanding. What's more, one of the probes, Voyager 1, is beginning to "taste" another realm beyond the "bubble" created by our Sun - the heliosphere. It's about to break free and become our first interstellar emissary.
But, like the infinite well analogy, Voyager 1 isn't about to hit the "bottom", it's going to keep transmitting its precious data back to Earth until its nuclear energy becomes so weak its instruments completely fail, possibly by the end of this decade.
So what "dragons" has Voyager 1 detected out there in the dark?
The Voyager Program was a huge undertaking for NASA. Intended to check out the outer planets of the solar system, Voyager 1 and its twin Voyager 2 completed the "grand tour" exploring Saturn, Jupiter, Uranus and Neptune. The exquisite beauty of the gas giants and their satellites stunned the world. The famous "Pale Blue Dot" photograph was snapped by Voyager 1 in 1990 (by the request of Carl Sagan), a photograph that gave us a perspective we've never seen before. But little did mission managers realise that in the year 2013 we'd still be "talking" to the probes as they recede deeper into the black.
"Voyager 1 can smell the whiff of interstellar shores - but it can't be called an interstellar probe, yet."
After 35 years, Voyager 1 has travelled over 18 billion kilometres (or 123 Astronomical Units - that's over three times the distance of Pluto to the Sun). To put that another way, Voyager 1 is so distant that it takes over 17 hours for a signal sent from Earth to reach the probe's antennae. It is therefore over 17 light-hours away. Voyager 1 is the most distant (and fastest) manmade object ever sent into space, but it is still minuscule considering it takes over 4 years for light to travel to our nearest star, Proxima Centauri.
The ageing probe was most recently thrown into the limelight when mission scientists realised the probe was detecting drop-off in the number of low-energy particles since 2009. These particles, mainly protons carried by the solar wind, have been detected in more or less the same quantities for the duration of Voyager 1's journey. In addition, the drop-off of low energy particles coincided with an increase in high-energy particles.
These high-energy particles are exciting - they originate from beyond the heliosphere. They are cosmic rays that originate from extreme events such as supernovae and black holes and are deflected by the heliosphere's outer edge, aptly named the "heliopause". The correlation seemed obvious at first; Voyager 1 was about to make a break for interstellar space!
As it turns out, although deeply fascinating, Voyager hasn't left the heliosphere quite yet, but it has entered a different and fascinating region.
The magnetic highway
As the solar wind blasts from the Sun, it travels past all the planets, asteroids and minor bodies, eventually reaching a point where the external interstellar gasses overwhelm the weakening solar wind flow. This point creates a boundary between the heliosphere and the interstellar medium. The flow of the solar wind gets weakened and eventually ceases to flow outward.
The detection of a weakening of solar wind particles led many to believe that Voyager 1 was passing through the outermost boundary of the heliopause, but when dealing with heliospheric scales, it's not a simple case of jumping from one medium to another; the heliopause is a huge interface and with the help of Voyager 1, we've been given an insight to the structure of this mysterious place.
Late last year during the much-anticipated announcement from Voyager scientists, NASA released science results from Voyager 1, detailing that the probe had drifted into a new and unexpected region of the heliopause nicknamed the "magnetic highway". The probe had flown straight into a wash of buckled magnetism and a mixture of particles originating from the Sun and interstellar space. This is a fascinating region where the magnetic field from the Sun is being swept back and a stream of high-energy particles from deep space are intermingling with the low-energy particles of the solar wind.
In other words, Voyager 1 can smell the whiff of interstellar shores - but it can't be called an interstellar probe, yet.
"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," Ed Stone, Voyager project scientist from Caltech in Pasadena, California, said in the December 2012 NASA announcement. "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."
Having worked on Voyager since its inception in 1972, the Caltech scientist has overseen the mission for over half his life. He is the embodiment of what it takes to manage an interstellar mission.
As discussed in previous Al Jazeera English articles, the distances between the stars are vast - they are so vast that it may seem that we are quarantined from the rest of the galaxy. But to some, these distances present a challenge, a challenge that is already being confronted head-on by a 35 year-old nuclear-powered robot that's making a run for interstellar space right at this moment.
Voyager 1 may not be aimed at any particular star, but it does represent human ingenuity on the grandest of scales. But to oversee such a mission, scientists (like Stone) must invest a lifetime of work. For even bigger interstellar concepts, whole generations of scientists will need to invest their time.
So, far from Voyager 1 being a mere curiosity, it has become our eyes and ears on the ultimate frontier. It's as if we've tossed that penny into a well of infinite space where no human can experience and, through the "eyes" and "ears" of our robotic emissary, we are discovering Voyager 1's dragons as she ploughs deep into the interstellar unknown, alone.
Ian O'Neill is Space Science Producer for Discovery News. He is also the founder and editor of space blog Astroengine.
Follow him on Twitter: @astroengine
The views expressed in this article are the author's own and do not necessarily reflect Al Jazeera's editorial policy.