The Nasa space probe was launched in 1977 and passed by Jupiter, Saturn, Uranus and Neptune before veering north.
It is now 10.8 billion miles from the sun travelling at a speed of 38,000 mph.
The solar wind, a stream of charged particles spewing from the sun, has slowed to a speed of zero and is moving sideways rather than outwards, marking the end of the solar system.
Nasa said the 722kg probe would take another four years to fully exit the solar system and enter interstellar space, the area between the influence of the sun and the next star system. The space agency described it as a “major milestone” in space exploration.
Its scientists first noticed changes in the solar wind around Voyager 1 in June but needed months of readings to confirm it.
The results were presented at a meeting of the American Geophysical Union meeting in San Francisco.
Rob Decker, a senior scientist at Johns Hopkins University, said: “When I realised that we were getting solid zeros I was amazed. Here is Voyager, a spacecraft that has been a work horse for 33 years, showing us something completely new again.”
The nuclear-powered craft is so far away that information from its instruments takes 16 hours to get back to Earth.
It was launched with a twin, Voyager 2, which is proceeding at a slower speed and is 8.8 billion miles from the Sun.
Though the primary purpose of the Voyager is to collect data, it does have an onboard message if any aliens should come across it. The Voyager Golden Record has "115 images and a variety of natural sounds, such as those made by surf, wind and thunder, birds, whales, and other animals... musical selections from different cultures and eras, and spoken greetings from Earth-people in fifty-five languages."
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