‘Black as Coal . . . Something Like Velvet’ : Comet Bigger and Darker Than Expected

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, does indeed have a black heart.

Scientists with experiments aboard the Giotto spacecraft reported today that the nucleus of Halley’s comet is twice as large as 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.

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

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. (Story, Page 4.) 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.

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

A Heart of Dirty Ice

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 peanut, unshelled.

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

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.”

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