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NASA has reported that its planetary probe, Voyager 1, has just burst through the Heliosphere and has entered inter-stellar space. This is the first time in history that man has sent a machine beyond the confines of the solar system.


The space inside our solar system is dominated by the solar wind, a storm of atomic particles and plasma blasted out continuously from the surface of our Sun. This solar wind pushes against the cosmic rays and gases of interstellar space to produce a bubble around the Earth.


Since the Sun is also moving through interstellar space at a speed of 25 km/s, it experiences a counter wind from the interstellar gases which presses into the bubble ahead of us and it is at this boundary that the Voyager craft has arrived, three times further out from the Sun than Pluto.

Voyager was launched on September, 5th, 1977, the same year in which Elvis Presley died. Its mission was to photograph Jupiter which it achieved two years later. It then used a novel technique to gain a speed that no terrestrial rocket could ever have given it.

As it entered the grasp of Jupiter’s gravitational field it used the planet’s high speed orbital motion to boost its own speed in a giant sling-shot towards Saturn which it reached 18 months later.

After taking snaps of Saturn’s rings it then used the same trick again to fling itself towards inter-stellar space.


Moving now at 17 km/s (over 60,000 km/h), the fastest moving object made by man, it took another 34 years to reach the limits of the Heliosphere, 19 billion kilometers away.

Having taken so long, its technology is four decades out of date with less computer capacity than an i-phone and with a radio transmitter only eight times more powerful. It is now so far away that even at the speed of light it takes 17 hours for a signal to arrive back at Earth by which time it has faded to a billion billionths of its original strength and can only be detected by integrating the reception of ten radio telescopes arrayed across the breadth of America.

Image of Voyager as seen by the radio telescopes (VLBA - the very large baseline array)

Image of Voyager as seen by the radio telescopes (VLBA – the very large baseline array)

The following diagram describes some of the functions of this amazing machine that has given us iconic images of Jupiter’s clouds and Saturn’s rings and is now sending back information on interstellar space. Its plutonium batteries have enough energy left to run the machine for another ten years after which it will become silent.