Message in a bottle

Give or take a few miles, a 36-year-old unmanned spacecraft is now about 12 billion miles from the Sun, a pretty incomprehensible distance whichever way you look at it.

And this week NASA's Voyager 1 spacecraft officially became the first human-made object to venture into interstellar space.

New data gathered during the summer indicate Voyager 1 has now been travelling for about one year through the plasma (ionized gas) of interstellar space, the space between stars.

Covering nearly a million miles a day, the nuclear-powered spacecraft, has well and truly crossed the boundary between the Sun's influence and interstellar space, sailing into the vast gulf between the stars to become humanity's first true starship.

The announcement was made this week by scientists at NASA’s JPL in California, including Voyager project scientist Ed Stone.

"In leaving the solar system and setting sail on the cosmic seas between the stars, Voyager has joined the other historic journeys of exploration such as the first circumnavigation of the Earth and the first footprint on the Moon," he said.

"This historic step is even more exciting because it marks the beginning of a new era of exploration for Voyager, the exploration of the space between the stars."

It may be a new era of exploration for humankind but in reality we’ll get only limited information from Voyager, partly because of the vast distances involved and also because its instruments are being to wear out.

The fact that some are working even now is testament to the robust design of a spacecraft that was only ever meant to gather data from a spectacular journey through the giant planets of our solar system.

Voyager 1 reached the boundary of the heliosphere in 2004, a milestone marked by readings showing the speed of the solar wind had dropped below that of sound. But it took another nine years to complete the crossing and move out into interstellar space.

The actual transition likely occurred in August last year but an instrument that would have confirmed that failed in 1980, forcing scientists to rely on less direct methods of observation.

As it turned out, the Sun cooperated, blasting huge clouds of charged particles and magnetic energy in Voyager 1's direction in March 2012. When the particles finally got there 13 months later, they created detectable vibrations in the electrically charged plasma surrounding the spacecraft.

After studying those waves, scientists concluded the density of the material was 40 times higher than it would be if Voyager 1 was still in the heliosphere.

The heliosphere is defined by the Sun's magnetic field and is filled with electrically charged particles blasted away from the Sun in all directions -- the solar wind.

Our Sun, its planets, moons, asteroids and comets are embedded in a vast, t teardrop-shaped region, or bubble, in space known as the heliosphere.

Voyager 2 was launched on 20 August 1977 and Voyager 1 lifted off on 5 September the same year. Both probes carry gold discs with recordings designed to portray the diversity of culture on Earth - just incase they are ever intercepted by distant intelligent life forms.

The probes were launched on different trajectories. Voyager 2′s so-called 'slow' trajectory enabled it to visit all four giant planets, while Voyager 1′s faster trajectory meant it would head into deep space after visiting Jupiter and Saturn.

Voyager 1 is now the furthest human-built object from Earth and the distance is so vast that it takes 17 hours now for a radio signal sent from Voyager to reach receivers on Earth.

It is expected that their plutonium power sources will stop supplying electricity in about 10 years, at which point their instruments and 20W transmitters will die. After that Voyager 1 will not approach another star for nearly 40,000 years.

When Voyager 1 blasted into space the world we live in was a very different place and much has changed in the intervening decades, both socially and from a technological perspective.

The Voyager spacecraft was designed to run most of its operations itself and computing power was impressive for its time.

Each probe has three interconnected computer systems: one to control the craft’s flight and altitude, another to control its instruments, and a third to manage the first two.

The computers can process about 8,000 instructions per second - a fraction of the capability of a modern smartphone, which handles upwards of 14 billion each second. With memory measured in kilobytes, the Voyager computers can hold only hold a few thousand words worth of text.

Probably the most intriguing piece of technology onboard Voyager is the legendary ‘Golden Record’ - a phonograph record packaged with a cartridge and needle, operating instructions and loaded with information about Earth.

It contains 115 images of humans, animals and airports, spoken greetings in languages from Akkadian to Chinese, a message from US President Carter and an eclectic 90 minute selection of music.

Carrying such a disc as it travels in silence though the depths of space, Voyager 1 is effectively humanity’s interstellar ‘message in a bottle’ - speeding ever outwards through the ocean of interstellar space towards the edge of forever.