Probe Records Halley’s Heart in Riot of Color

A small European spacecraft survived just long enough to get the job done Thursday, dropping out of contact with Earth immediately after sending back the closest pictures ever of the nucleus of Halley’s comet.

Traveling 50 times faster than a speeding bullet, Giotto carved its niche in history as it plunged through the heart of the comet, snapping photographs as it passed about 300 miles from Halley’s icy core.

Brilliant Colors

Halley appeared in the photographs as though it were painted by a madman, sporting brilliant hues wrapped around a glistening center. The colors were not the real colors of the comet itself, but were instead “false colors” used by scientists to designate areas of common brightness.

But they created a surrealistic portrait of the famous comet, which has returned every 76 years to tantalize mortals who have stared at the heavens in awe.

The photographs appeared to have stripped the cloaks of dust and gas that Halley’s has draped itself in for centuries.

The Real Nucleus

“We think this is the iceberg. We can assume this is the real nucleus we are seeing,” Rainer Schwenn, a member of the camera team, said as the photographs flashed across scores of television sets at the European Space Operations Center here.

To Schwenn’s practiced eye, the photos revealed “incredible detail.”

He said he detected contours on the nucleus, and he said he could tell the difference between ice and dust on the surface.

While the camera clicked away, nine other experiments aboard Giotto examined the comet’s magnetic field, captured and analyzed dust particles, and studied the gases and ionized particles that make up the plasma field that surrounds the nucleus.

Scientists will analyze that data for weeks before figuring out what it all means, but they were elated here Thursday by the fact that all of the experiments seemed to have worked perfectly.

It was not known for certain why Giotto’s signal dropped dramatically just as the craft made its closest approach, but preliminary indications were that the craft had been so bombarded by dust that it started wobbling, and that would have kept Giotto’s antennas from pointing toward Earth.

The craft was being bombarded at the “high rate” of 120 impacts per second during the last two minutes of the encounter.

Scientists, however, were elated over the images they saw, convinced they had at last seen the nucleus of Halley’s comet.

“Halley had kept its true face hidden from us all, until tonight,” a triumphant Reimer Lust, director general of the European Space Agency, told an ecstatic crowd here.

Enormous Energy

Halley and Giotto passed each other at more than 150,000 m.p.h.--a speed so great that a grain of dust hitting the spacecraft would have had the same kinetic energy as a crash with a small car.

The close encounter was the grand finale of the greatest week in the history of cometary science, during which the most famous wanderer in the solar system was visited by no less than five spacecraft that had traveled for up to 27 months to get there.

The space probes, sent by the Soviet Union and Japan in addition to the member nations of the European Space Agency, also signaled somewhat of a turning point in the history of the space age.

This was the first effort at interplanetary exploration by both Japan and Europe. The success of Giotto moved Europe forcefully into the competition for major scientific achievement in space, and the two Japanese spacecraft that successfully completed their modest goals proved that Japan’s neophyte program is off and running.

“We have established our technology to go out into deep space,” said Hiroki Matsuo of the Institute for Space and Astronomical Science in Tokyo. “We have passed the initiation into this interplanetary society, which has been monopolized by the two giants.”

International Success

The success of the missions to Halley’s marked a major milestone in international cooperation. One of the more difficult parts of the Giotto mission involved sending the spacecraft that close to the comet, yet managing to miss the hard, ice nucleus.

That was accomplished partly by determining the location of the comet in relation to the Soviet spacecraft on the basis of information supplied by the Soviets. That, plus information from the huge antennas of the U.S. space tracking network that told the Europeans exactly where the Soviet probes were, allowed the Europeans to target their spacecraft with utmost precision.

Named Pathfinder

The international effort was called Pathfinder.

Roald Sagdeyev, head of Moscow’s Space Research Institute, noted that the navigational achievement permitted the Europeans to target their spacecraft on a comet that bears the name of “the greatest navigator of his century,” Sir Edmond Halley.

Halley was the first to prove that some comets follow orbits around the sun, and he predicted correctly that the comet, later named after him, would return years after his own death.

The first photograph from Giotto arrived here about three hours before the closest approach, and although it was shot while the craft was still 465,000 miles from the comet, it offered a striking study in false colors.

Seeking Answers

Researchers hoped that Giotto would clear up confusion that arose during Halley’s encounter last week with two Soviet probes.

Scientists in Moscow at first said that the earliest images from Vega 1 suggested that Halley might have two nuclei instead of one--a suggestion that many cometary experts immediately rejected because such a finding would not fit neatly with the current understanding of the way comets behave.

Less than a day later, Soviet scientists said that what had appeared as a second nucleus was gas jetting out from the comet.

But Roald Sagdeyev, director of Moscow’s Space Research Institute, told scientists and reporters here that the best images from Vega do, in fact, suggest that the nucleus has a “double structure.” Sagdeyev said the nucleus is odd in shape and larger than expected.

Irregular Shape

“The implication is that the nucleus is a very irregular shape, like a potato,” he said. He added that Vega images also indicated that the nucleus is about six miles long and possibly half that wide, and if it isn’t in two pieces it is at least “double shaped,” he said.

Although solar collectors on both Vega 1 and Vega 2 were damaged extensively by dust from Halley, both spacecraft have about half their electrical generating capacities still functioning.

The Soviet experiences with Halley’s dust caused considerable concern because Giotto was set to go 10 times closer than the Vega probes.

Rudiger Reinhard, project scientist for Giotto, said European officials were encouraged by Vega 1, which found less dust than had been expected. But the picture changed considerably when Vega 2 passed the comet and found that while there was less dust, the particles were bigger.

Period of Rotation

Reinhard said Halley apparently has “one active hemisphere and one inactive hemisphere.” The comet rotates once every 52 hours, and Giotto’s flyby was to occur during the time when the “inactive” side was exposed to the sun.

Unfortunately, Reinhard said, although the “inactive” side emits fewer dust particles, they are much larger in size and thus potentially more dangerous.

That led European scientists to reduce the odds of a safe passage, but they still insisted that Giotto had at least an 80% chance of functioning throughout the entire encounter.

Part of the concern grew out of the fact that Giotto has no recording equipment to capture data during the flyby and subsequently send it back to Earth. Project directors decided that since there was a reasonable chance that Giotto would be either destroyed by dust or tilted so that its antenna would no longer point to Earth, the emphasis would be placed on transmitting data back immediately rather than on recording it for later use.

Delicate Balance

That meant, however, that if dust tipped the craft just one degree it would lose radio contact with Earth and all would be lost.

Giotto was launched on July 2 by an ESA Ariane 1 rocket from Kourou, French Guiana. The one-ton, cylindrical probe, which is 9 1/2 feet long and 6 feet in diameter, is carrying sophisticated equipment for 10 on-board experiments.

Giotto was named after the Italian master who spotted the comet nearly 600 years ago, then painted it in one of his works.

The comet is the best known and brightest of about 1,000 comets that periodically pass the Earth.