The spacecraft Pioneer-10, mission to explore the outer solar system, seemed destined to perish. But it survived the asteroid belt, intense radiation near Jupiter and a flyby with a mysterious object beyond Pluto.
Launched March, 1972, Pioneer still performs valuable scientific observations. Funding was almost severed a few years ago. Scientists studying chaos theory became interested in detecting faint radio transmissions from the edge of the solar system. Mission leader Larry Lasher calls the project a blessed “white knight.”
Pioneer is looking to detect the outer reaches of the heliosphere, an elliptical field of solar wind that radiates from the sun. At the edge, where the solar system meets outer space, the interstellar ray flux abruptly stops the solar winds.
During Pioneer’s 28-year voyage, it has traveled almost 7 billion miles, about twice the distance of Pluto from the sun. At the speed of light, a radio signal would not reach the spacecraft for 10.3 hours, one way. Voyager 1 and Pioneer-10 are both traveling away from the sun, although in almost exactly opposite directions.
Pioneer was the first spacecraft to photograph Jupiter and pass beyond Pluto’s orbit. It charted Jupiter’s intense radiation belts and verified that the Jovian planet is mostly liquid.
No one knew if a spacecraft could navigate the asteroid belt between Mars and Jupiter. The hurling boulders in this cosmic minefield were as big across as the width of Texas. Pioneer traversed it virtually untouched. Resultantly, other voyages beyond Mars were planned.
At the edge of the solar system, Pioneer-10 is now about 75 astronomical units away from the sun, or 75 times the distance of the Earth from the sun.
Data from the spacecraft is still being received by a sensitive radio telescope. The craft’s nuclear-powered battery supply is barely functional. Activating its instruments, NASA’s Ames Research Center fears, would result in a permanent power outage. The craft was recently maneuvered into a new position to improve signal reception on Earth. To do this, scientists turned off its transmitter for 90 minutes.
At about 5.2 billion miles from Earth, Pioneer was knocked off course by a mysterious gravitation tug. Astronomers think it was caused by a Kuiper Belt Object (KBO), asteroid-sized bodies far beyond Pluto in orbit of the sun.
NASA anticipates the boundary to be a distance of 75 to 125 AUs. Pioneer and veterans Voyager 1 and 2 spacecraft swashed the earlier theory that the heliosphere extended only to Jupiter. All three spacecraft are now beyond the outer planet, Pluto.
In 1998, Pioneer became the most distant manmade object within the solar system. Pioneer is expected to stop sending transmissions in the next few years but will continue to drift into interstellar space for eternity.
Launched five years later, in 1977, the Voyagers both flew by Saturn and Jupiter. Voyager 2 also passed near Uranus and Neptune. The Voyagers are heading in the opposite direction from Pioneer, in relationship to the sun.
Gravity from Saturn’s moon Titan caused Voyager 1, traveling 39,000 miles per hour, to fly out of the ecliptic plane in which all the planets but Pluto orbit, and into outer space. Voyager 1 and 2 are still functioning, exploring the outer solar system.
In 1979, Voyager 1 and Voyager 2 passed by Jupiter, sending back data that convinced scientists there were rings around the largest planet. The Voyager spacecraft also discovered three new satellites of Jupiter before venturing out to the most distant planets.
In late 1998 as the spacecraft had nearly reached the edge of the solar system, Voyager 2 lost contact with ground tracking. After a 66-hour frenzied communications blackout, mission scientists reestablished contact with Earth. No one quite knows why the plutonium energy source hiccuped. NASA’s Jet Propulsion Laboratory in Pasadena plans to continue Voyager’s five remaining experiments until 2020.
Having used planetary gravitation to reach escape velocity from the solar system, Pioneer is traveling toward the red star Aldebaran, the eye of Taurus the Bull, at 27,380 mph. Pioneer will arrive there in two million years or so. By the time our sun expands into a red giant and obliterates Earth, it will probably still be drifting through the galaxy 5 billion years hence.
In the extremely remote possibility that other sentient life might find Pioneer, they may learn about humans. On board is a plaque, designed, in part, by the late Dr. Carl Sagan, engraved with pictures, solar maps and elemental symbols to describe civilization on Earth.
The Pioneer-10’s mission officially ended on March 31, 1997, but it is
still partially functional, and NASA scientists occasionally check in on it.