We won't believe it until Nasa announces it - but suspicions are growing that the Voyager 1 space craft really has left the Solar System.
The craft is currently close to the edge of the heliosphere - the area where the Sun's influence can be felt through magnetic fields and charged particles.
Launched in 1977, Voyager 1 has explored Jupiter, Saturn and now taken itself to the very edge of our galactic neighbourhood. Both Voyager 1 and Voyager 2, also launched in 1977, are capable of sending back data until at least 2020.
In fact, it is now so close to the edge that generally it is thought to be in a 'transition zone' about 18 billion kilometers from Earth, where counts of solar particles suddenly drop off and galactic electrons and protons rise in number.
But judging the exact point where it leaves this sphere of influence and enters inter-stellar space for real is very difficult - leading to confusion when some groups claim it has crossed the boundary, but Nasa continues to deny it.
Earlier this year many news outlets - including us - reported that the boundary had been crossed, and that Voyager had become the first man-made object to leave the Solar System, only for Nasa to say that while "multiple crossings of a boundary unlike anything previously observed" had been recorded, the craft was still just on the inside of the bubble.
But now the University of Maryland has said its best guess is that the crucial line has been crossed.
"It's a somewhat controversial view, but we think Voyager has finally left the Solar System, and is truly beginning its travels through the Milky Way," says UMD research scientist Marc Swisdak, lead author of a new paper published online this week in The Astrophysical Journal Letters.
The key to their findings is the theory that the edge of the solar system is not in fact a clean boundary, but a series of pourous structures where loops in magnetic fields lead to "fundamental instabilities" in particle counts.
In a statement Nasa's Ed Stone said that the new model was intriguing, but not definitive.
"Details of a new model have just been published that lead the scientists who created the model to argue that NASA's Voyager 1 spacecraft data can be consistent with entering interstellar space in 2012. In describing on a fine scale how magnetic field lines from the sun and magnetic field lines from interstellar space can connect to each other, they conclude Voyager 1 has been detecting the interstellar magnetic field since July 27, 2012. Their model would mean that the interstellar magnetic field direction is the same as that which originates from our sun.
Other models envision the interstellar magnetic field draped around our solar bubble and predict that the direction of the interstellar magnetic field is different from the solar magnetic field inside. By that interpretation, Voyager 1 would still be inside our solar bubble.
The fine-scale magnetic connection model will become part of the discussion among scientists as they try to reconcile what may be happening on a fine scale with what happens on a larger scale.
The Voyager 1 spacecraft is exploring a region no spacecraft has ever been to before. We will continue to look for any further developments over the coming months and years as Voyager explores an uncharted frontier."