This artist's rendering shows NASA's Voyager spacecraft. The two long thin rods extending out to the left are antennas used by the Plasma Wave instrument. The Planetary Radio instrument also used these antennas when it was turned on.
Credit: NASA
Voyager's golden record cover.
Credit: NASA
MARYLAND: More than 30 years after they left Earth, NASA's twin Voyager probes are now at the edge of the Solar System, and with each passing day they are beaming back a message that, to scientists, is both unsettling and thrilling.
Among the top Voyager discoveries are the discovery of volcanoes on Jupiter's moon Io; evidence for an ocean beneath the icy surface of Europa; hints of methane rain on Saturn's moon Titan; the crazily-tipped magnetic poles of Uranus and Neptune; icy geysers on Neptune's moon Triton; planetary winds that blow faster and faster with increasing distance from the Sun.
"It's uncanny," said Ed Stone of Caltech, Voyager Project Scientist since 1972. "Voyager 1 and 2 have a knack for making discoveries. "Each of these have changed the way we thought of other worlds."
Only Uranus and Neptune visit
The adventure began in the late 1970s when the probes took advantage of a rare alignment of outer planets for an unprecedented Grand Tour.
Voyager 1 visited Jupiter and Saturn, while Voyager 2 flew past Jupiter, Saturn, Uranus and Neptune. Voyager 2 is still the only probe to visit Uranus and Neptune.
In 1980, Voyager 1 used the gravity of Saturn to fling itself slingshot-style out of the plane of the Solar System. In 1989, Voyager 2 got a similar assist from Neptune. Both probes set sail into the void.
What lies inside the heliosphere
Stone set the stage by directing our attention to the kitchen sink. "Turn on the faucet," he instructed. "Where the water hits the sink, that's the sun, and the thin sheet of water flowing radially away from that point is the solar wind. Note how the sun 'blows a bubble' around itself."
Researchers call this bubble the 'heliosphere', and it is gargantuan. Made of solar plasma and magnetic fields, the heliosphere is about three times wider than the orbit of Pluto.
Every planet, asteroid, spacecraft, and life form belonging to our solar system lies inside.
The unpredictable heliosheath
The Voyagers are trying to get out, but they're not there yet. "As the water (or solar wind) expands, it gets thinner and thinner, and it can't push as hard. Abruptly, a sluggish, turbulent ring forms. That outer ring is the heliosheath - and that is where the Voyagers are now," said Stone.
The heliosheath is a very strange place, filled with a magnetic froth no spacecraft has ever encountered before, echoing with low-frequency radio bursts heard only in the outer reaches of the solar system, so far from home that the sun is a mere pinprick of light.
"In many ways, the heliosheath is not like our models predicted," said Stone.
