Tale of a Comet

Jules Verne is credited with a vision of space travel unrivalled in his century.

His imaginative leaps were completely unbounded in his 1877 serialization called "Off on a Comet", in which a band of explorers are taken aboard a comet called Gallia, following its unexpected collision with Earth. Indeed, in his time, already 169 asteroids had been mapped in astronomical catalogs, and the beginning of an active debate on their terrestrial collision risks was just ensuing.

The painting titled "K/T Hit" by artist Donald E. Davis. This impact occured 65 million years ago, ending the reign of the dinosaurs.
Image Credit: Don Davis

Verne’s explorers take the reader on a tour of the solar system, only to return safely to Earth full of the knowledge of how the Earth might look from afar, and how other celestial bodies like Jupiter could capture a photographer’s dreams. Carried with them on their fantastic trip was a large chunk of what formerly was terrestrial land, particularly Tunisia and Gibraltar.

Verne correctly attributed that given the distance of his travellers from the Sun, that the comet would resemble an ice-ball, not the fiery world that appears periodically as the comet dust trails away under solar wind pressure. He wrote: "The solidity of the ice was perfect; the utter stillness of the air at the time when the final congelation of the waters had taken place had resulted in the formation of a surface that for smoothness would rival a skating-rink; without a crack or flaw it extended far beyond the range of vision."

But "Off on a Comet" is also a reflection of its time. The notion of safe travel of any kind, much less one beyond Saturn, is impossible without protective measures. Like a cartoon in which only inches from impact, a character steps safely off of a falling elevator, Verne’s characters likewise follow an unlikely safe transit to their home planet. But their tall-tale provides a mini-tour of how the solar system might have looked to astronomers a century ago.

In the next 5 years, five encounters of spacecraft are planned with comets and asteroids.

Excerpt from Jules Verne’s "Off on a Comet", 1877

The Moment of Impact

Whence came it that at that very moment the horizon underwent so strange and sudden a modification, that the eye of the most practiced mariner could not distinguish between sea and sky?

Fragments of Comet P/Shoemaker-Levy 9 colliding with Jupiter (July 16-24, 1994).
Credit: NASA

Whence came it that the billows raged and rose to a height hitherto unregistered in the records of science?

Whence came it that the elements united in one deafening crash; that the earth groaned as though the whole framework of the globe were ruptured; that the waters roared from their innermost depths; that the air shrieked with all the fury of a cyclone?

Whence came it that a radiance, intenser than the effulgence of the Northern Lights, overspread the firmament, and momentarily dimmed the splendor of the brightest stars?

Whence came it that the Mediterranean, one instant emptied of its waters, was the next flooded with a foaming surge?

Whence came it that in the space of a few seconds the moon’s disc reached a magnitude as though it were but a tenth part of its ordinary distance from the earth?

Whence came it that a new blazing spheroid, hitherto unknown to astronomy, now appeared suddenly in the firmament, though it were but to lose itself immediately behind masses of accumulated cloud?

What phenomenon was this that had produced a cataclysm so tremendous in effect upon earth, sky, and sea?

Artist’s depiction of the Chicxulub impact crater. About 2,225 near-Earth objects (NEOs) have been detected, primarily by ground-based optical searches, in the size range between 10 meters and 30 kilometers, out of a total estimated population of about one million; some information about the physical size and composition of these NEOs is available for only 300 objects. The total number of objects a kilometer in diameter or larger, a size that could cause global catastrophe upon Earth impact, is now estimated to range between 900 and 1,230.
Credit: NASA

Was it possible that a single human being could have survived the convulsion? and if so, could he explain its mystery?

The Incredible Predicament

The only intelligible words which the astronomer had uttered had been, "My comet!"

To what could the exclamation refer? Was it to be conjectured that a fragment of the earth had been chipped off by the collision of a comet? and if so, was it implied that the name of the comet itself was Gallia, and were they mistaken in supposing that such was the name given by the savant to the little world that had been so suddenly launched into space? Again and again they discussed. these questions; but no satisfactory answer could be found.

On the night of the 31st of December, a comet, crossing the ecliptic, had come into collision with the earth, and that the violence of the shock had separated a huge fragment from the globe, which fragment from that date had been traversing the remote inter-planetary regions.

"We imagine that we are on a considerable fragment of the terrestrial globe that has been detached by collision with a planet to which you appear to have given the name of Gallia."

All previous hypotheses, then, were now forgotten in the presence of the one great fact that Gallia was a comet and gravitating through remote solar regions.

Gallia would accomplish her revolution in precisely two years, and would meet the earth, which would in the same period of time have completed two annual revolutions, in the very same spot as before. What would be the consequences of a second collision they scarcely ventured to think.

Meanwhile, a marvelous world, never before so close within the range of human vision, was revealing itself. Throughout those calm, clear Gallian nights, when the book of the firmament lay open before him, he could revel in a spectacle which no previous astronomer had ever been permitted to enjoy.

And what an increased interest began to be associated with the [Jovian] satellites! They were visible to the naked eye! Was it not a new record in the annals of science?

Cassini Jupiter
Detail stripes from rotating storms in background, one of Jupiter’s moon in foreground Credit: NASA/JPL Cassini

For everyone could so far distinguish them one from the other as to describe them by their colors. The first was of a dull white shade; the second was blue; the third was white and brilliant; the fourth was orange, at times approaching to a red.

As their return to the earth appeared to them to become more and more dubious, they abandoned their views of narrow isolation, and tried to embrace the wider philosophy that acknowledges the credibility of a habitable universe.

"Suppose," they say, "an observer endowed with an infinite length of vision: suppose him stationed on the surface of [the star] Capella [340 millions of millions of miles away]; looking thence towards the earth, he would be a spectator of events that had happened seventy years previously; transport him to a star ten times distant, and he will be reviewing the terrestrial sphere of 720 years back; carry him away further still, to a star so remote that it requires something less than nineteen centuries for light to reach it, and he would be a witness of the birth and death of Christ; convey him further again, and he shall be looking upon the dread desolation of the Deluge; take him away further yet (for space is infinite), and he shall be a spectator of the Creation of the spheres. History is thus stereotyped in space; nothing once accomplished can ever be effaced."

The Big Sling Shot

Artist’s concept of Muses-C spacecraft, flying down toward the asteroid.
Credit: ISAS

The object, however, of supreme interest was the great expanse of the terrestrial disc, which was rapidly drawing down obliquely towards them. It totally eclipsed an enormous portion of the firmament above, and approaching with an ever-increasing velocity, was now within half its average distance from the moon. So close was it, that the two poles could not be embraced in one focus. Irregular patches of greater or less brilliancy alternated on its surface, the brighter betokening the continents, the more somber indicating the oceans that absorbed the solar rays. Above, there were broad white bands, darkened on the side averted from the sun, exhibiting a slow but unintermittent movement; these were the vapors that pervaded the terrestrial atmosphere.

This vague aspect of the earth soon developed itself into definite outlines. Mountains and plains were no longer confused, the distinction between sea and shore was more plainly identified, and instead of being, as it were, depicted on a map, the surface of the earth appeared as though modelled in relief.

Icy-rock core of Halley’s Comet

And, truly, if they could have paused to study it, that panorama of the states of Europe which was outstretched before their eyes, was conspicuous for the fantastic resemblances with which Nature on the one hand, and international relations on the other, have associated them. There was England, marching like some stately dame towards the east, trailing her ample skirts and coroneted with the cluster of her little islets; Sweden and Norway, with their bristling spine of mountains, seemed like a splendid lion eager to spring down from the bosom of the ice-bound north; Russia, a gigantic polar bear, stood with its head towards Asia, its left paw resting upon Turkey, its right upon Mount Caucasus; Austria resembled a huge cat curled up and sleeping a watchful sleep; Spain, with Portugal as a pennant, like an unfurled banner, floated from the extremity of the continent; Turkey, like an insolent cock, appeared to clutch the shores of Asia with the one claw, and the land of Greece with the other; Italy, as it were a foot and leg encased in a tight-fitting boot, was juggling deftly with the islands of Sicily, Sardinia, and Corsica; Prussia, a formidable hatchet imbedded in the heart of Germany, its edge just grazing the frontiers of France; whilst France itself suggested a vigorous torso with Paris at its breast.

The glowing expanse of the earth’s disc seemed like a vast funnel, yawning to receive the comet and its atmosphere, balloon and all, into its open mouth.

In a mystery every one found himself upon the earth again. They could not explain it, but here they were once more upon terrestrial soil; in a swoon they had left the earth, and in a similar swoon they had come back!

Animation of Sun’s spectacular greeting to passing comet tail. Click image for larger picture. GIF Animation 180 kB. Also see full disk (480 kb) and gallery animation Credit: NASA/ESA/SOHO

"Where on earth have you been to all this time? In the name of peace, what have you been doing with yourself?"

Disbelief of a Dream

In spite of the denial which astronomer after astronomer gave to the appearance of such a comet as Gallia at all, and of its being refused admission to the catalogue, he published a voluminous treatise, not only detailing his own adventures, but setting forth, with the most elaborate precision, all the elements which settled its period and its orbit. Discussions arose in scientific circles; an overwhelming majority decided against the representations of the professor; an unimportant minority declared themselves in his favor, and a pamphlet obtained some degree of notice, ridiculing the whole debate under the title of "The History of an Hypothesis."

"What is a man to believe?"

What’s Next

On Jan. 2, 2004, the spacecraft called Stardust will fly within 75 miles of a cometary main body (called Wild-2), close enough to trap small particles from the coma, the gas-and-dust envelope surrounding the comet’s nucleus. Stardust will be traveling at about 13,400 miles per hour and will capture comet particles traveling at the speed of a bullet fired from a rifle. The main camera, built for NASA’s Voyager program, will transmit the closest-ever comet pictures back to Earth. Launched in February 1999, Stardust was designed to capture particles from Wild 2 and return them to Earth for analysis. The spacecraft already has collected grains of interstellar dust. It is the first U.S. sample-return mission since the last moon landing in 1972.

In the next 5 or so years, there will be no fewer than five encounters of spacecraft with comets and asteroids. All the following missions are fully funded, though only not all have already been launched (the others will follow in 2003 to 2004):

2001 Sept. 22 Comet Borrelly Deep Space One (simple flyby)  
2003 Nov. 12 Comet Encke CONTOUR (simple flyby)
2004 Jan. 1 Comet Wild 2 Stardust (coma sample return)
2005 July 3 Comet Tempel 1 Deep Impact (big mass impact)
2005 Sept. Asteroid 1998 SF36 Muses-C (sample return)


Related Web Pages

Great Impact Debate I: Benefits of Hard Bodies
Great Impact Debate II: Much Ado About Nothing?
Impact Hazards Website
NASA/JPL Near Earth Object Program
Mini Solar System
Cosmic Dust (Univ. Wash, St. Louis)
Stardust (JPL)
University of Washington (Seattle)
Don Brownlee (U of Wash)