Voyager 1 leaves the solar system
Voyager 1 has crossed a new frontier, becoming the first spacecraft ever to leave the solar system, Nasa said.
Thirty-six years after it was launched from Earth on a tour of the outer planets, the plutonium-powered spacecraft is more than 11.5 billion miles from the Sun, cruising through what scientists call interstellar space - the vast, cold emptiness between the stars, the US space agency said.
Voyager 1 actually made its exit more than a year ago, according to Nasa. But there is no clear boundary line, and it was not until recently that Nasa had the evidence to support what an outside research team claimed last month: that the spacecraft had finally ploughed through the hot plasma bubble surrounding the planets and escaped the Sun's influence.
While some scientists said they remain unconvinced, Nasa celebrated. "It's a milestone and the beginning of a new journey," said mission chief scientist Ed Stone at Nasa's Jet Propulsion Laboratory.
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, where the Voyager team awaits the starship's discoveries.
The interstellar ambassador also carries a gold-plated disc containing multicultural greetings, songs and photos, just in case it bumps into an intelligent species.
Voyager 1's odyssey began in 1977 when the spacecraft and its twin, Voyager 2, were launched on a tour of the gas giant planets of the solar system. After beaming back dazzling postcard views of Jupiter's giant red spot and Saturn's shimmering rings, Voyager 2 moved on to Uranus and Neptune. Meanwhile, Voyager 1 used Saturn as a gravitational slingshot to power itself past Pluto.
Voyager 1, which is about the size of a small car, carries instruments that study magnetic fields, cosmic rays and solar wind.
Last year, scientists monitoring Voyager 1 noticed strange happenings that suggested the spacecraft had broken through - charged particles streaming from the Sun suddenly vanished. At the same time, there was a spike in galactic cosmic rays bursting in from the outside. Since there was no detectable change in the direction of the magnetic field lines, the team assumed the far-flung craft was still in the heliosphere, or the vast bubble of charged particles around the Sun.
The Voyager team patiently waited for a change in magnetic field direction - thought to be the tell-tale sign of a cosmic border crossing. But in the meantime, a chance solar eruption caused the space around Voyager 1 to echo like a bell last spring and provided the scientists with the information they needed, convincing them the boundary had been crossed in August last year.