ON March 2, 1971, a doughty little spacecraft named Pioneer 10 began its first year in space. It's an anniversary worth remembering.
The 250-kilogram (550-pound) craft has made history during the past two decades as the first spacecraft to negotiate the asteroid belt, the first craft to pass by Jupiter, and the first human-made object of any kind to leave the solar system and head for the stars. It also carries the first engraved greeting from Earth to any intelligent aliens Pioneer 10 may encounter. This is a gold-anodized plaque showing the figures of a man and woman, the sun's location relative to 14 objects called pulsars that emi t distinctive radio signals, and a sketch of Pioneer 10 leaving the solar system.
It's worth noting, as a footnote to history, that Cornell University astronomers Carl Sagan and Frank Drake designed the plaque at the suggestion of three reporters, one of whom was then a science writer for The Christian Science Monitor. In his book "By Jupiter, Odysseys to a Giant" (Columbia University Press, 1982) that writer, Eric Burgess, tells how the concept came to him.
He writes: "I visualized how Pioneer 10 escaping from the Solar System would become mankind's first emissary to the stars.... It should carry a message that would tell any finder of the spacecraft a million or even a billion years hence that planet Earth had evolved an intelligent species that could think beyond its own time and beyond its own Solar System."
Freelance writer Richard Hoagland and Don Bane, then with the old Los Angeles Herald-Examiner, also latched on to the idea.
For a spacecraft with a design lifetime of 21 months, Pioneer 10 has proved to be extraordinarily rugged. Seven of its 11 instruments still work. It still returns useful data on particles and electromagnetic fields as it approaches the so-called heliopause where the sun's sphere of influence gives way to interstellar space, traveling at about 46,500 kilometers an hour (28,900 miles an hour). The manufacturer - TRW Inc. - says the craft should continue to report back until at least the year 2000.
Pioneer 10 is not alone in its interstellar odyssey. Its twin - Pioneer 11 - left Earth April 5, 1973. It too has moved beyond the solar system in a direction more or less opposite to Pioneer 10's course. Then there are the two Voyager craft whose stunning planetary photography has overshadowed that of the Pioneers.
These four craft are all sampling unknown space as they move toward the heliopause in four different directions. Their data are helping scientists sketch a three-dimensional picture of space dominated by the sun. This will help give perspective to data from the international Ulysses solar explorer, which also is sampling unknown space as it moves on a course passing over the sun's north and south poles.
The Voyager craft also carry earthly greetings. These are more sophisticated than the Pioneer plaques for they feature sounds and pictures. They are all what Eric Burgess calls "intellectual cave paintings, marks of Man." They should be preserved in space for billions of years. The plaque on Pioneer 10 was the first of these to leave. It's now 8 billion kilometers from Earth.
Nice going Eric!