SCIENCE

A celestial encounter

JOHN BARBER March 24 1986
SCIENCE

A celestial encounter

JOHN BARBER March 24 1986

A celestial encounter

SCIENCE

As the spacecraft Giotto hurtled toward the core of Halley’s comet last week, scientists at the European Space Agency’s control centre in Darmstadt, West Germany, strained to describe the extraordinary images flickering on their video screens. Some of them said that the pictures, which Giotto was transmitting to Earth every four seconds, made the comet look like a malformed potato. Others compared it to a peanut or a banana. The scientists will refine those descriptions as they study the mass of data that Giotto transmitted before a storm of cometary dust killed its signal 90 million miles away from Earth. At the same time, computers will convert the crude video images into highresolution photographs. But one thing is already clear: thanks to Giotto, the mysterious celestial traveller will never look the same again.

Giotto’s mission was simple and daring: to pierce the cloud of dust and gas that surrounds the comet’s icy core. It was a deliberately suicidal run that ESA scientists said would destroy the $380-million spacecraft and the equipment for 10 scientific experiments that it carried. And as Giotto approached the comet at 43 miles per second, it ran into what ESA spokesman Peter Wenzel called “a wall of dust the size of grains of sand.” But the specially

armored spacecraft—which is as big as a compact automobile—kept transmitting data until it was 430 miles away from the comet’s core, two seconds and about 100 miles short of its planned destination. In those final few seconds, the spacecraft, named after a 14th-century Italian painter, transmitted more information on the appearance and composition of a comet than Earthbound observers had gained over thousands of years.

Giotto’s kamikaze-style approach ended when it resumed transmitting data from the other side of the comet, 25 minutes after its presumed destruction. And according to U.S. National Aeronautics and Space Administration official Burt Edelson, the mission was “an absolute triumph of international co-operation”; Giotto was guided in the final hours of its eight-month flight by information supplied by two Soviet spacecraft, Vega I and Vega 2, which reconnoitred the comet earlier this month. The Western Europeans and the Soviets have agreed to pool all their data in an international archive that should keep space scientists busy for decades—at least for another 76 years, when Halley’s comet will wheel back around the sun and yield more of its mysteries.

—JOHN BARBER in Toronto