This week, we bid farewell to a true pioneer: Pioneer 10, the first spacecraft to leave our solar system.
NASA last received a signal from Pioneer 10 on January 22. A February attempt failed, and last week NASA announced there would be no more attempts.
That final faint signal traveled more than 12 billion kilometers—a distance so great that at the speed of light, just under 300,000 kilometres per second, it still took 11 hours and 20 minutes to make the journey. Pioneer 10 is now more than twice as far away from the sun as Pluto, the outermost planet.
Its epic journey began on March 2, 1972. Setting off on what was originally intended to be only a 21-month mission to Jupiter, Pioneer 10 set a new speed record right away, its three-stage Atlas/Centaur rocket accelerating it to 51,810 kilometres per hour, making it the fastest manmade object to leave the Earth—so fast it passed the Moon in just 11 hours and crossed Mars’s orbit just 12 weeks later.
The firsts kept coming. On July 15, 1972, Pioneer 10 became the first manmade object to enter the Asteroid Belt. In movies, asteroid belts are so thick with rocks you can almost jump from one to the other, but the real-life asteroid belt is still mostly empty space, and Pioneer 10 made it through unscathed.
Pioneer 10 reached Jupiter on December 3, 1973, took 500 close-up pictures, charted the planet’s intense radiation belts—and kept going. It passed within 130,354 kilometres of the planet, accelerated to 132,000 kilometres per hour (thanks to Jupiter’s gravity) and went hurtling into the outer reaches of the solar system, sending back information about the solar wind (energetic particles expelled by the sun) and cosmic rays (energetic particles coming the other way, from deep space).
In 1983, Pioneer 10 passed through the orbit of Neptune, then the outermost planet (at the time Pluto’s eccentric orbit had it inside Neptune’s orbit), becoming the first manmade object to leave the solar system. Its scientific mission officially ended on March 31, 1997, but NASA continued to track it as part of a study of communications technology for future interstellar probes.
Last March, NASA decided to try to “wake up” the spacecraft to see if it could provide any information about the heliopause, the point at which the solar wind can no longer be detected. To the controllers’ surprise and delight, Pioneer 10 responded, and sent back data for two months. But after that, although its signal could be detected, no more telemetry followed; and now, even its signal has vanished.
It’s amazing NASA could track it as long as it did. Built with 1960s technology, the three-metre long Pioneer 10 boasted a transmitter that put out all of eight watts—equivalent to a nighlight. By the time its signal reached Earth, it was only a millionth of a trillionth of a watt. But NASA’s Deep Space Network of radio telescopes was up to the task.
Pioneer 10 will pass the star Aldebaran, 68 light years away, in approximately two million years. By then it may be one of the few remnants of our species. But should some other intelligent species find it, it carries a kind of a greeting card to tell them who we were and where we lived.
Designed by Dr. Carl Sagan and Dr. Frank Drake, and drawn by Dr. Sagan’s wife, Linda Salzman Sagan, the etched gold anodized aluminum plaque, 15.25 by 22.8 centimetres, shows the nude figures of a man and a woman, drawn to scale next to a line silhouette of the spacecraft. Bracketing bars to the woman’s right include the binary notation for the number eight, indicating she is eight units tall; the measuring unit is then defined with another drawing as a particular hydrogen wavelength, common throughought the universe, that measures 20.32 centimetres.
A radial pattern shows the position of the Sun relative to 14 pulsars and the center of the Galaxy; another diagram shows the relative distances of the solar system’s planets from the sun, and indicate that Pioneer 10 came from the third planet of that system.
Pioneer 10 is no longer the furthest spacecraft from the solar system; Voyager 1, heading in almost the opposite direction, exceeded Pioneer 10’s distance on February 17, 1998, and since then has been extending its advantage by more than 150 million kilometers a year. It carries its own message, a gold-plated copper phonograph record carrying images, sounds and greetings from Earth.
It’s unlikely any of them will be intercepted by aliens; but if one of them is, I hope it’s Pioneer 10.
After all the firsts it’s racked up, it deserves one more.