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Drawing of the split comet Biela, from Amedee Guillemin's The Heavens (1868).
 

Apr 10, 2007
The Chicago Fire (2)
Where was Comet Biela?

A strange thing happened to comet Biela in 1845. The nucleus of the comet split into two partners. The “smaller” comet (lower left in the picture above), subsequently became more active and brighter than the larger. And that was only the beginning.

In 1883, twelve years after the Chicago fire, Ignatius Donnelly published a widely read book, Ragnarok: the Rain of Fire and Gravel. Though the book dealt primarily with the evidence for cometary disasters in ancient times, Donnelly suggested that the Chicago fire provided a small glimpse of the terror experienced by our earlier ancestors. “There is reason to believe that the present generation has passed through the gaseous prolongation of a comet's tail, and that hundreds of human beings lost their lives”.

Reflecting on the simultaneous events around Lake Michigan on the evening of October 8, 1871, Donnelly posed the underlying mystery: “At that hour, half past nine o'clock in the evening, at apparently the same moment, at points hundreds of kilometers apart, in three different states, Wisconsin, Michigan, and Illinois, fires of the most peculiar and devastating kind broke out, so far as we know, by spontaneous combustion”. (We take up the historic testimony cited by Donnelly and others in tomorrow’s “Picture of the Day”).

Donnelly believed he could identify the cause of the devastation. He said it was Comet Biela, a comet that captured attention from astronomers in 1826, returned for a few predictable visits, broke into two nuclei, and then disappeared.

The comet was named after Austrian officer W. von Biela, who observed the body in February 1826.  By following the path of Biela, the French astronomer Marie-Charles-Théodore de Damoiseau estimated the time of its return. He said the comet would cross the orbit of the Earth about one month ahead of our planet’s arrival at the same spot.

Donnelly does not mention that ten days after Biela’s announcement, a French astronomer John Felix Adolphe Gambart also sighted the comet. Both Biela and Gambert calculated the orbit, recognizing that earlier comet apparitions in 1772 and 1805 were the same object that appeared in 1826. And Gambert, along with other astronomers, predicted that the comet would strike the earth on its return, which he projected for October 29, 1832.

Damoiseau’s prediction was correct. Earth missed the comet by about a month.

On its anticipated 1846 return, Biela was first sighted in late 1845 as it moved toward perihelion (its closest approach to the Sun), astronomers were surprised to see that the head of the comet had acquired a faint satellite. It had split in two (picture above), something we now know to be fairly common for comets, but still mysterious to cometologists. In 1845, the event seemed unprecedented. As noted by Carl Sagan and Nancy Druyan in their book Comet, “the finding was so bizarre that the first astronomer to note this twinning dismissed it as some internal reflection in his telescope”.

In Robert Chapman’s and John Brandt’s The Comet Book certain details of Biela’s return are fascinating. The discovery of a partner occurred on January 13, 1846, when “a faint satellite comet was observed a small distance from the main comet”. Two tails were seen parallel to each other. “Over the next month the fainter of the two comets increased in brightness and finally became brighter than the ‘main’ comet. The situation then reversed and the main comet became the brighter one again. In addition, the main comet grew a second tail and a luminous bridge of material joined the two comets” [emphasis ours].  At this time the two nuclei were apart an estimated 250,000 kilometers, about two thirds of the distance separating Earth and the Moon.

Donnelly’s account at this point diverges from the history told by Chapman and Brandt. As Donnelly tells it, “In 1852, 1859, and 1866, the comet should have returned, but it did not”.  But Chapman and Brandt—prominent figures at NASA’s Goddard Space Flight Center at the time of their book’s publication—say that the twin comet-heads did indeed appear at the appointed time in 1852. This reappearance is, in fact, well documented. And one detail in Chapman’s and Brandt’s account rarely shows up in standard discussions of cometology:

“…Both comets returned at the predicted time, though they were over 2 million kilometers apart [emphasis ours]. Once again the two comets took turns as the brighter of the pair. On at least one occasion a bright jet was seen between the two heads” [emphasis ours].

Though Sagan and Druyan report the splitting of Biela, they do not mention the jet, an event for which the standard view of comets has no theoretical reference.

The rest of Donnelly’s discussion of Biela is in general agreement with the summary by Chapman and Brandt. Amazingly, and with the aid of a startling and unpredicted meteor shower on November 27, 1872, Professor W. Klinkerfues of Berlin, calculated the trajectories of the meteoric falls, concluding that they were the remains of the comet. This, in turn led him to send instructions to Norman Pogson, Government Astronomer at the Madras Observatory in India (far enough south to allow a good view). Pogson’s answer to Klinkerfues, dated December 6, said he “found Biela immediately” on the first clearing of the sky, and on the second day he saw it again. It showed no tail, he said.

As Chapman and Brandt put it, this was either an “incredible coincidence”, or it was the actual last view of the comet.

The spectacular meteor shower that inspired Klinkerfues to identify it with Biela has long since become an annual event—sort of—called the Andromedids. And astronomers do not hesitate to connect the shower to Biela.  Each year the Earth passes through the remains of the comet, but with widely varying consequences. And the effect today is trivial by comparison with the November 1872 occurrence. Today the shower peaks around mid-November, averaging less than three meteors per hour—hardly deserving the title “shower”. On the night of November 27, 1872, however, records show several thousand meteors per hour—a direct and obvious link to the disintegration of the comet.

It remains to be asked, then, whether the fragmentation of Biela, a comet on a path intersecting the orbit of the Earth, and predicted by some astronomers to collide with the Earth in 1832, might have been the source of the “great conflagration” in 1871. The comet had split at least 25 years earlier (the 1846 appearance), and the two partners had separated by more than 2 million kilometers by 1852. So whether or not Klinkerfues observed Biela after the spectacular shower of November 1872, we know he did not report seeing two bodies. Hence, at least one of the partners intersecting Earth’s path had presumably already disintegrated entirely, leaving the possibility that on a subsequent orbit the Earth moved into debris left by the body.

The facts on the Andromedids, including their erratic occurrence over the years and the obvious dispersal and depletion of the cometary debris over a century and a half, cannot give us a definitive answer to Donnelly’s views on Biela. But as for plausibility, the answer is definitive. Many facts are consistent with the interpretation, and there are no facts that exclude the interpretation.

Of course, it is not necessary to identify an intruder, in order to see the evidence of an intrusion. No one questions the exploding Tunguska comet, asteroid or meteor on the basis that astronomers cannot identify the incoming object.

But of all the scientific details about comet Biela, perhaps none stands out more dramatically than the fact almost never mentioned—a jet forming between the two nuclear fragments when they were 2 million kilometers apart. In the purely gravitational and mechanical terms that astronomers have sought to apply to comets, this jet is inconceivable. But when we remember how inconsequential is gravity in the presence of the electric force, the improbability disappears.

In fact, the jet is a clue more vital by far than the popular “scientific” commentary on Donnelly’s hypothesis. By directing our attention to the electrical nature of comets, it also invites us to look again at the historic testimony, with an eye to details long unnoticed or forgotten.

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