WHILE IT WON'T sharply affect the terms of life on this planet, the most extraordinary event of the past week was surely Pioneer Ten's passage beyond Neptune. It has now crossed the outer limit of the solar system and continues serenely on its course. Originally built to operate in space for 21 months, Pioneer is now in its 12th year of flawless operation. Its designers think that it will continue its transmissions for perhaps another decade.

Astronomers knew quite a lot about the solar system before the space probes, but they suffered the limitation of a single perspective. With them, science is suddenly able to see from other angles. Pioneer and its successors, the Voyager spacecraft, have now produced a wealth of information that will refine and expand understanding in ways that cannot be fully assessed for many years.

Because the physics of the very large and the very small is one unbroken web, the galaxy and the atom continually provide clues to each other's structures. Current theory of the origin of the universe comes chiefly from the study of subatomic particles and, conversely, particle physics often turns to astronomy for confirmation of its insights. You can never know what purpose it will serve to learn a little more about, say, the radiation belts around Jupiter. But experience suggests that whatever you find will tell you about much more than Jupiter alone.

Pioneer is continuing to provide news and commentary about the solar winds through which it is now sailing. In time it will finally cease to transmit. Then it will finally be lost to its inventors--lost, but also safe. It is now in a region where no accident can befall it. In some 10,500 years Pioneer will pass, at some distance, a star. In terms of the voyage on which it is now embarked that is fairly soon.

By the reckoning of the world that it has left, how long a time is that? Ten thousand years ago homo faber, as the academics sometimes call us--man who makes things--had acquired considerable skill with small tools of stone and bone. But we had no agriculture then, and were farther from Cheops' pyramid than Cheops is from us today.

Pioneer's journey seems altogether likely to run for hundreds of thousands of years and conceivably much longer. Even if homo faber manages by an uncharacteristic application of intelligence not to blow up this planet, astronomy says that the sun will eventually collapse in a natural death. Machines often outlive their inventors. But it is remarkable to think that at some unimaginable reach of space Pioneer may become the farthest memorial of a solar system that no longer exists.