Advertisement
Share

Halley’s Comet, Indeed, Has Heart ‘Black as Coal’

Times Science Writer

It turns out that a dirty snowball that has returned to Earth every 76 years, sometimes lighting up the heavens so starkly that it was viewed as a harbinger of doom and destruction, indeed has a black heart.

Scientists with experiments aboard the Giotto spacecraft reported Friday that the nucleus of Halley’s comet is twice as large as they had expected but “black as coal” on the surface.

“It is the darkest dark you can imagine,” Uwe Keller, principal investigator for Giotto’s multicolor camera, told a packed press conference at the European Space Operations Center here.

Giotto plunged through a river of fine dust as it ripped past the comet’s core, missing the hard nucleus by a scant 375 miles. Although it was severely damaged in the process, the craft sent back enough data to allow scientists to paint a profile of the fabled wanderer.

Engineers with the European Space Agency will not know for several days whether they can save the spacecraft.

Advertisement

It will take scientists weeks to draw final conclusions on what the results from the experiments actually mean.

However, the data from Giotto, combined with information from two Soviet spacecraft that viewed the comet from different angles earlier this month, should answer many of the questions that have puzzled scientists for centuries. Halley’s Comet is believed to have originated around the time of the solar system’s formation about 4.6 billion years ago.

The comet emerges as an irregularly shaped object wrapped in a cloak of thick, black dust, warmed by the sun to a surface temperature of about 85 degrees, all masking a heart of dirty ice.

Roald Sagdeyev, director of the Soviet Space Research Institute in Moscow, described the nucleus as looking a little like a “potato.”

Others suggested it looks more like a giant, unshelled peanut.

“A peanut, a potato, a banana, whatever,” Keller snorted, “we know now it is highly irregular and black, something like velvet.”

Surprised Scientists

Photographs from Giotto reveal that the nucleus is more than nine miles long and at least three miles wide, an irregularity that surprised scientists, who concluded long ago that the relatively smooth course followed by Halley indicated the nucleus was spherical.

Ray Newburn of Pasadena’s Jet Propulsion Laboratory, who has seen photos that have not yet been released by the European Space Agency, said one photo shows gas and dust streaming from the comet in what “looks like an eruption coming out of the nucleus.”

It may be that irregular features on the surface of the nucleus act like jet nozzles, focusing the gas that fires out of the comet’s icy center as it is warmed by the sun, said Newburn, co-chairman of the International Halley Watch.

The “jets” are probably formed by holes in a thick mantle of dust that blankets the nucleus, he said.

Fred Whipple, a legendary figure among cometary scientists and the creator of the image of comets as “dirty snowballs,” said Halley’s mantle is black because “the dust undoubtedly contains carbon and organic material.”

First Glimpse

“It’s truly exciting,” said Whipple, 79, a man who has waited for many years for his first glimpse at the nucleus of a comet.

Halley proved a little more than Giotto could handle. Giotto, named after the 14th-Century Italian painter who used Halley’s comet to represent the Star of Bethlehem in his painting, “The Adoration of the Magi,” lost contact with Earth at almost the exact moment of its closest approach.

The craft was bombarded by between 1,000 and 2,000 dust particles--traveling at a relative speed of 150,000 m.p.h.--as it shot past the nucleus. The dust particles were extremely fine or, in the words of one scientist, “a million times smaller than a grain of cigarette smoke.” But at times it streams from the comet at the rate of about 60 tons per second.

David Wilkins of South Wales, flight operations manager for Giotto, said more than 100 tiny dust particles blasted through the shield designed to protect the spacecraft from the cloud of gas and dust that surrounds the comet. That caused the craft to wobble suddenly, cutting off contact with Earth.

Giotto was not destroyed, however.

The craft took command of its own systems, just as it was designed to do. About 40 minutes later, it had stabilized itself to the point that it was able to again begin transmitting data back to Earth.

But by then the close encounter was over.

Major Goals

The major goals of the mission had already been accomplished when the signal was lost, although scientists had hoped to photograph the comet as the craft sped away, which would have supplied different views that could be used to recreate three-dimensional models.

“We lost an appreciable part of the potential (for the photographic results),” Keller said. “We wanted to look at the comet from the other side.”

All 10 experiments worked perfectly up to the point of closest encounter, scientists reported, although data was lost during the period when communications blacked out. Giotto carries no recording equipment, so there is no way to recover the loss.

Several instruments, including the camera, were damaged by impact as Giotto zipped through the dust storm.

Sometime within the next few days, engineers will try to fire up Giotto’s maneuvering rockets to see if the craft can be recycled for another mission. If successful, they will put Giotto into a “parking orbit,” in which it would drift to a point about 12,000 miles from Earth in 1990, and possibly redeploy it to another target.

If the maneuver fails, “Giotto will be gone,” said Roger Bonnet, director of scientific programs for the project.


Advertisement