Voyager: Beyond the Great Beyond

Hurtling through the frigid expanse beyond the planets, NASA’s aging spacecraft Voyager 1 has reached the edge of the Solar System, where it has encountered a massive shock wave, according to two paper that will be published in Nature by a team of scientists. Voyager‘s journey through this turbulent zone will give scientists the first direct measurements of our solar system’s unexplored final frontier, the heliosheath. Scientists are debating whether this passage has already begun.

The doppler effect
Credit: NASA


Let the Debates Begin


Sounds of Earth



Beyond the Great Beyond

More than eight billion miles from Earth, the farthest an operating spacecraft has ever journeyed, Voyager 1 is providing scientists with data from a fascinating yet little understood region of space – the frontier where the Sun’s influence begins to wane, and the tenuous vastness of interstellar space takes over.

It is here that charged particles streaming out from the Sun – called the solar wind – bump into the ionized gas and dust that is spread thinly between stars, causing a shock wave in the process. The termination shock is where the solar wind, a thin stream of electrically charged gas blown constantly from the Sun, is slowed by pressure from gas between the stars. At the termination shock, the solar wind slows abruptly from its average speed of about 700,000 to 1,500,000 miles per hour.

Estimating the location of the termination shock is hard, because we don’t know the precise conditions in interstellar space. We do know speed and pressure of the solar wind changes, which cause the termination shock to expand, contract and ripple.

"When the Voyager missions were launched in 1977, we never thought the instruments we developed more than three decades ago would one day probe the edge of the Solar System," said Louis Lanzerotti of Bell Labs, an expert on how the solar wind affects terrestrial communications. Lanzerotti has been involved with NASA’s Voyager missions since their inception in 1972. Launched on September 5, 1977, Voyager 1 explored the giant planets Jupiter and Saturn before being tossed out toward deep space by Saturn’s gravity. It is approaching, and may have temporarily entered, the region beyond termination shock. At more than 13 billion kilometers (approximately eight billion miles) from the Sun, Voyager 1 is the most distant object from Earth built by humanity.

"Voyager 1 and 2 provided us with unparalleled views of the planets. I find it very exciting that Voyager 1 will soon begin to explore the vastness of the interstellar medium," he said.

Astronomers now know that the space between stars, once thought to be completely empty, is filled with a dilute plasma of gas and dust termed the interstellar medium. The solar wind blows out a giant bubble called the heliosphere within the interstellar medium, and the boundary between the heliosphere and the interstellar medium is a place where a lot of interesting physical phenomena take place.

Much like a shock wave precedes a supersonic airplane, astronomers think that a "termination shock" occurs near the edge of the solar system. This is a region where the speed of the solar wind drops dramatically as the wind brakes as it mixes with the interstellar medium, and where the density of ionized particles increases many times. It is also a region where some ions from the interstellar medium, relics of previous generations of stars, manage to diffuse through the edge of the Solar System and are accelerated tremendously.

Using an instrument on Voyager 1 called the low energy charged particle detector, Lanzerotti and his colleagues found evidence of all three effects. They saw a hundred-fold increase in the number of charged particles detected during a six-month period starting in August 2002; they deduced that the speed of the solar wind had dropped by a factor of seven; and they detected ions that came from beyond the Solar System.

"When we saw all that, we were pretty sure that we had reached the termination shock," Lanzerotti said. Lanzerotti is a distinguished research professor in physics and at the Center for Solar Research, New Jersey Institute of Technology.


V-ger, Spock investigates ancient probe. The alien from the original 1983 film Star Trek, The Motion Picture. V-ger, as it called itself (pronounced vee-jer) was an ancient mechanical space probe that was on a mission to explore and discover and report back its findings. Captain Kirk discovers that the probe was called Voyager 6, which had been launched by humans on Earth in the late twentieth century. Apparently, the ‘oya’ that fits between the ‘V’ and the ‘ger’ had been badly tarnished and was unreadable.
Credit: Paramount

As the Krimigis team analyzed its data from Voyager 1, it noticed something strange. It seemed that after six months, in early 2003, the termination shock region moved outwards, possibly as a result of increased solar activity. Scientists postulate that the heliosphere is a dynamic entity, which expands and contracts with the Sun’s 11-year activity cycle.

"Solar eruptions must have caused the solar wind to pick up speed," said Lanzerotti. "That forced the heliosphere to expand outwards, and the termination shock must have moved outwards as well. Voyager 1 will probably encounter it again."

The Krimigis team expects to get confirming data from a similar detector on Voyager 2, which is expected to follow Voyager 1 to the edge of the Solar System. The Voyager probes, among NASA’s most successful spacecraft, are expected to provide data until approximately 2020, when they will exhaust their power supply from nuclear isotopes and drift off into space. Still operating in remote, cold and dark conditions 26 years later, the Voyagers owe their longevity to these generators, which produce electricity from the heat generated by the natural decay of plutonium dioxide.

"Meanwhile, they will continue to provide a treasure trove of wonderful, sometimes unanticipated data about the far reaches of the Solar System and push the frontiers of our knowledge," Lanzerotti said. Data of how the solar wind behaves will provide scientists with knowledge useful not only to astronomy but to terrestrial concerns such as how solar emissions affect wireless telephone calls, satellite communications and electric power grids.

What’s Next



Voyagers 1 and 2 were built by JPL, which continues to operate both spacecraft 26 years after their launch. The spacecraft are controlled and their data returned through NASA’s Deep Space Network, a global spacecraft tracking system also operated by JPL. The Voyager Project Manager is Ed Massey of JPL.

Related Web Pages

Voyager Mission NASA/JPL
Voyage of The Voyagers: First Quarter-Century
Voyager Music Playlist
Deep Space Network