Space: Peering into Halley's Heart

As the Giotto spacecraft and Halley's comet raced toward each other last week at a closing speed of 155,000 m.p.h., the tension at the European Space Agency's control center in Darmstadt, West Germany, became palpable. Images of the cornet, relayed to the center at intervals of four seconds, loomed larger and larger on television screens, finally yielding by far the best look yet at an elongated shape near Halley's heart. It was the comet's nucleus. Giotto Investigator Wolfgang Schmidt, giving a play-by-play description of the images, could not contain his excitement. "It's obvious that there is structure on this nucleus," he exclaimed. "Mountains, hills, craters--incredible detail!" Suddenly the image froze and then, only two seconds before the spacecraft's closest approach to the comet, the screens went blank.

One of the worst fears of the international Giotto team, it seemed, had been realized. Fully aware of the dangers of meeting any outsize dust particles at the tremendous speed of encounter but determined to get a closeup look, the scientists had aimed the spacecraft to swoop only 338 miles from Halley's dust-shrouded nucleus. That, according to Roger Bonnet, ESA's director of scientific programs, was like playing Russian roulette: "You may survive, but one shot will kill you."

It was indeed a gamble. In the last seconds before the encounter, Giotto ran into what one scientist described as a "wall of dust the size of grains of sand." The spacecraft's protective dust shields were peppered with particles at a rate of 100 impacts a second, a bombardment that swung its antenna out of alignment with a tracking station in Australia. That brought communications to a halt. But before the blackout, Giotto relayed more than 2,000 images of Halley's back to earth, plus a torrent of data from the ten on-board instruments.

At the control center, cheers rang out and champagne corks popped. Then came the bonus. Half an hour after the screens blacked out, Giotto's signals were picked up again; except for the camera, all of its instruments were still working.

Although scientists will be interpreting Giotto's data for months to come, Horst Keller, principal investigator of the camera team, announced some preliminary results. Halley's nucleus appeared to be 9.4 miles long and at least 2.5 miles wide, he said, and the surface, "velvet black and very irregular, with an indentation in the middle, like a peanut or a potato." On one side of the nucleus were what appeared to resemble nozzles, spewing out one minor and two major jets of gas and dust. Keller was puzzled by the blackness of the nucleus, which suggested that there is little or no ice on its surface. Astronomer Fred Whipple, whose concept of a comet as a "dirty snowball" was apparently confirmed by earlier findings of the Soviet Vega probes, offered a possible explanation: the comet's surface might be covered by densely packed, extremely small particles embedded in an icy mantle.

Giotto's grand finale was preceded by the flybys of the second Soviet Vega and two Japanese craft. Early in the week, Vega 2 passed 5,125 miles from the comet's nucleus, sending back 700 pictures and confirming that the nucleus was solid. But the dust clouds encountered by the craft disabled nearly half of its solar panels and two of its experiments.