The Voyager 1 probe has become the first spacecraft to ever leave our solar system, Nasa said on Thursday.

NASA's Voyager 1 spacecraft officially is the first human-made object to venture into interstellar… http://t.co/EqMxh54c66

— NASA (@NASA) September 12, 2013

Thirty-six years after it was launched from Earth, the plutonium-powered Voyager is now more than 11.5 billion miles from the sun in interstellar space.

The US space agency said Voyager 1 actually left the solar system more than a year ago, but it was only recently it had enough evidence to confirm it has gone through the hot plasma bubble that surrounds the planets.

An artist's impression of the Voyager spacecraft at the heliosphere edge

Ed Stone, mission chief scientist at Nasa's Jet Propulsion Laboratory, said: "It's a milestone and the beginning of a new journey."

Voyager 1 will now study exotic particles and other phenomena in a never-before-explored part of the universe and radio the data back to Earth.

The spacecraft is carrying a gold-plated disc containing multicultural greetings, songs and photographs, in case it meets intelligent life.

Its journey began in 1977 when it and its twin, Voyager 2, were launched on a $988m tour of the gas giant planets.

An artist's impression of the probe

After sending back postcard views of Jupiter's giant red spot and Saturn's rings, Voyager 2 moved on to Uranus and Neptune.

Voyager 1 used Saturn as a gravitational slingshot to power itself past Pluto.

The size of a small car, it carries instruments that study magnetic fields, cosmic rays and solar wind.

Last year, scientists noticed strange happenings suggesting the spacecraft had broken through the heliosphere - a vast bubble of charged particles around the sun.

Voyager 2 is trailling behind its twin and could take another three years before it breaks through the heliosphere.

Eventually, they will run out of nuclear fuel and will have to power down their instruments, perhaps by 2025.