The Voyager 1 spacecraft, traveling through interstellar space after leaving the solar system, is having a bumpy ride as it moves through a cosmic "tsunami wave" in space, scientists say.

First encountered earlier in this year, the wave is still moving outwards, new data suggests, and is the longest-lasting such wave yet detected in interstellar space, scientists say.

Occurring when the sun emits a coronal mass ejection of magnetic plasma from its surface, the resultant pressure wave, when it collides with interstellar plasma, creates shock waves in that interstellar medium.

"Most people would have thought the interstellar medium would have been smooth and quiet," says Don Gurnett from the University of Iowa. "But these shock waves seem to be more common than we thought."

Voyager 1 has encountered three such shock waves since leaving the solar system in 2012, and in fact researchers says it is those very shock waves that confirm the space probe has left the heliosphere, the bubble created by the solar wind that encompasses the sun and the planets and marks the outer boundary of our solar system.

The current wave was detected by Voyager 1 in February and is still going, according to November magnetic field data from the spacecraft received here on Earth.

"The tsunami causes the ionized gas that is out there to resonate -- 'sing' or vibrate like a bell," says Ed Stone at the California Institute of Technology in Pasadena.

From the time of the first detection of the current wave until now, Voyager 1 has traveled a quarter of a billion miles, scientists say.

How far such cosmic tsunamis can travel into space before they fade away is unknown, says Gurnett.

"I'm guessing it could be another hundred astronomical units or more," he says.

An astronomical unit is around 93 million miles, the mean distance between the Earth and the Sun; Voyager 1 is currently at a distance of about 130 A.U. from the sun, about 12 billion miles.

And it is not alone in providing scientists with ongoing discoveries from distant space at and beyond the boundary of our solar system; a sister craft, Voyager 2, is currently at 109 A.U. from the sun and making it own approach to the heliosphere.

"We're hoping it will happen in the next couple of years," says Stone.

Voyager 1 and its twin Voyager 2 launched in 1977. Both space probes flew past Jupiter and Saturn, while Voyager 2 also conducted flybys of Uranus and Neptune.