There are five man-made probes that are destined to leave the solar system, never to return - the two Pioneers, the two Voyagers and New Horizons. In addition there are various rocket stages that will also, albeit more slowly, end up in inter-stellar space.

Voyager 1 is currently the most distant of these probes at approximately 25 billion kilometres from home. It has already breached the heliosphere but will still have to navigate the Oort cloud for thousands of years to come. It is operating at the very edge of its capacity, one that will inevitably end in decade or so.

Recently Nasa sent a command to Voyager 1 telling it to turn on one of its heaters. Something was lost in translation (it takes 23 hours for the signal to reach the craft) and Voyager appeared to cease radio contact. Strangely enough, it popped up again on a different radio frequency, having inexplicably turned on an old transmitter that was last used in 1981!

The investigation into the how and why continues. But these stories and the legends that these little probes will create for themselves will be enduring.

Image courtesy Discovery magazine.