“You would see one particular spot in the sky for just 30 seconds, but with a telescope that big, that was good enough to discover lots of interesting things,” Wolszczan says. He calls it “cowboy science” — going for a ride just to see what’s out there.
Wolszczan’s roughly 10-day trot through the sky paid off quickly with the detection of a special kind of pulsar, called a millisecond pulsar, that rotates hundreds of times each second. At the time, it was only the fifth such object ever found. The pulsar now bears the designation PSR B1257+12 (PSR for pulsar, the rest indicating its sky coordinates), and Wolszczan affectionately refers to it as “1257.” But he was not feeling so affectionate back then as he attempted to explain the peculiarly irregular timing of radio pulses from this city-size star: “It was really a lot of pain because the pulsar didn’t want to fit any standard models. I just had to struggle with it.”
In short order, Wolszczan realized that the Arecibo data made sense if a small object were pulling the pulsar back and forth, causing its signal to arrive a little early at some times, a little late at others. By June 1990 he was certain that an orbiting planet was the only sensible explanation, but it took painstaking analysis to prove that PSR B1257+12 actually has three planets, called A, B and C.
He knew his results would be scrutinized closely: These would be the first confirmed planets beyond our solar system, found in a place where most people thought planets could not exist. Did he have any doubts before he went public? “No. That may sound a little bit strange, but pulsar timing is an extremely precise method,” he says.
In January 1992, Wolszczan announced his results at a meeting of the American Astronomical Society. Planets B and C are each about four times the mass of our world. Planet A is a mere 1/50th of an Earth mass, just slightly heftier than the moon. It is still, by far, the smallest known planet around another star. What followed was a wave of wonder and confusion. A wide variety of influences, from Copernicus to Carl Sagan, had convinced astronomers that the galaxy must be full of other solar systems much like our own. Now at last, here was an airtight discovery of planets orbiting another star, and everything about them was all wrong. “Everybody expected planets around normal stars. They were wondering, ‘What is going on?’ ” Wolszczan recalls.
The inferred life story of PSR B1257+12 could hardly be more different from the story of our solar system. Our sun is middleweight and modest; the star that evolved into the pulsar started out massive and dazzling. Earth and its neighboring planets arose as part of the sun’s birth; the pulsar planets emerged from their star’s death.
Wolszczan sketches out a history that goes like this: In its youth, the star that became PSR B1257+12 had at least eight times the mass of the sun. Goaded by the force of its prodigious gravity, it burned bright and hot, consuming the bulk of its nuclear reserves in just a few million years. At the end of its life, the star exploded as a supernova, flinging most of its material outward violently. All that remained was an ultradense, fast-spinning fragment of the original star’s core — the pulsar. Any planets that might have existed in orbit before the supernova were eradicated in the conflagration. But the star’s transformation was not yet complete.
A disk of gas formed around the pulsar, originating either from a nearby companion star, or from the so-called supernova fallback material — part of the star’s expelled debris that did not develop enough speed to escape into space. That disk then condensed and gave rise to a new family of planets, composed of heavy elements created by the supernova.
Whole New Worlds
With his discovery, Wolszczan earned himself a place in the textbooks as the first person to find a new planet since the discovery of Pluto in 1930 (or, if you grumpily dismiss Pluto as a mere dwarf, since the discovery of Neptune in 1846). But PSR B1257+12 A, B and C quickly faded from the public consciousness. They were simply too weird, too unexpected. “The discovery didn’t fit in the NASA plan for extrasolar planets. It did not fit in a very dramatic way, and that showed in the reactions of people,” Wolszczan says. Starting in 1995, other astronomers found planets around nice, proper, sunlike stars. Most of the scientific attention soon turned that way.