The Voyager 1 spacecraft was launched in early September 1977 from Cape Canaveral on a course for the king of the planets, Jupiter, which it reached on March 5, 1979. It was not the first human probe to fly past that planet—Pioneer 10 and Pioneer 11 beat it by a few years—--but its dramatic pictures and amazing discoveries, such as the sulfur volcanoes on the satellite Io, captured the public imagination far more so than did the results of those more primitive probes.
After zooming past Jupiter, Voyager 1 reached Saturn a year and a half later, on November 12, 1980. The story was similar: more dramatic pictures and amazing discoveries, such as the incomprehensibly complex structure of Saturn's rings.
Voyager 1's course through the Saturn system was designed to give it a close look at the fascinating world Titan, whose thick atmosphere turned out to be opaque to Voyager's cameras, disappointing us armchair explorers at the time but helping lead to the great anticipation of the Cassini/Huygens mission that landed a probe on Titan earlier this year. This course past Titan prevented Voyager 1 from following a path onward to the other, at the time still unexplored, giant planets of the outer solar system, Uranus and Neptune. Its sister craft, Voyager 2, was left to study those worlds on its own, flying by them in 1986 and 1989, respectively. And, of course, sending back yet more dramatic pictures and amazing discoveries.
Instead, Voyager 1 found itself on a lonely, isolated path. No more landmarks on its route. Just a lot of virtually empty space.
For nearly 25 years.
Now, Voyager 1 finally has another landmark to study. There won't be any dramatic pictures, but amazing discoveries are a distinct possibility. Voyager 1 is the first human-made craft to reach the outer edges of the Sun's influence. It is now traversing the boundary zone between the Sun's zone and the interstellar medium itself.
From the Washington Post:
After a storied, 28-year odyssey, NASA's venerable Voyager 1 spacecraft appears to have reached the edge of the solar system, a turbulent zone of near-nothingness where the solar wind begins to give way to interstellar space in a cosmic cataclysm known as "termination shock," scientists said yesterday.
"This is an historic step in Voyager's race," said California Institute of Technology physicist Edward C. Stone, the mission's chief scientist since Voyager 1 and its twin, Voyager 2, were launched in the summer of 1977. "We have a totally new region of space to explore, and it's a once-in-a-lifetime opportunity."
Stone said project scientists, working from models of a phenomenon never before directly observed, finally agreed that data from Voyager 1's tiny 80-kilobyte computer memory showed that the spacecraft had passed through termination shock to the "heliosheath," a frontier of unknown thickness that defines the border with interstellar space.
Stamatios M. Krimigis, another longtime Voyager scientist, said in an interview that the spacecraft might remain in the heliosheath for perhaps 10 years but should easily survive, going dark when its plutonium power source expires around 2020.
When [Voyager 1] entered the heliosheath, it was 8.7 billion miles away -- the farthest any manmade object has traveled. Its speed is 46,000 mph.
Krimigis said the solar wind, made up of fast-moving electrons, protons and other charged particles, has a magnetic field that prevents the interstellar wind from breaching the solar envelope -- known as the "heliosphere" -- as the solar system travels through space.
The heliosheath is the heliosphere's outer frontier, a zone where the solar wind begins to dissipate. This process begins at termination shock and is marked by a sudden drop in the speed of the solar wind and a corresponding build-up in heat and the strength of the magnetic field. The effect is like traffic piling up on a freeway during rush hour.
Scientists first detected these symptoms in 2002, but they receded, then returned more strongly, only to recede again. It is a script not foreseen by the computer models.
"We've gone back and forth since then," Krimigis said. "But this time I guess we all agree." This is because the magnetic field jumped by a factor of 2.5 to 4 around Dec. 15 -- and has remained fluctuating at a high level since then, Krimigis said. Scientists estimated that the speed of the solar wind dropped from 1.5 million mph to near zero.
But wait, there's more.
Of far greater concern to scientists [than the spacecraft's long-term functionality] is the possibility that NASA could kill the $4.2 million-a-year project to free up money for President Bush's initiative to send humans back to the moon and eventually to Mars.
NASA has put Voyager's fate on hold while independent reviewers evaluate the mission, with a decision expected in February. "We're very excited," Krimigis said of the latest findings. "We hope NASA will reconsider, and we're confident they will."
I, too, am confident that NASA will not, in the end, pull the plug on Voyager, after decades of waiting, just as it reaches the cusp of interestellar space. It is quite cheap at this stage in its life. And it has a huge following of space buffs such as myself who followed its exploits back in our younger days. But that such an action was even being considered is not a good indication of the quality of recent decision-making at NASA headquarters.
Meanwhile, onward to the stars, Voyager.