The Mars Mystery: The Secret Connection Between Earth and the Red Planet Page 25

  Marsden spent three months going through all his calculations again. Then at the end of 1992 he made a further statement in which he affirmed that he was now certain that his original date of 11 July would be proved correct—give or take a day or two—and that there was therefore no danger of a collision in 2126.50 “Were safe for the next millennium,” he proclaimed, adding that the comet would make another close approach in the year 3044.51

  UNCERTAINTIES

  Astronomers watching Swift-Tuttle leave the inner solar system observed a recurrence of the Cape effect during 1993: “The comet ejected material that changed its path once again, albeit very slightly.”52 It then continued on its way, traveling so fast that by 1998 the most powerful telescopes on Earth were no longer able to pick it up. It will be seen next when it returns toward perihelion in 2126, with hope closer to 11 July than 26 July.

  With a diameter of 24 kilometers, Swift-Tuttle will then be traveling at just over 60 kilometers per second. If by some bad fortune Marsden turns out to be wrong and it does hit Earth, speed/mass calculations indicate that the impact energy will be “in the range of 3 to 6 billion megatons.”53 This would be equivalent to between 30 and 60 impacts on the scale of the K/T event 65 million years ago.

  Could there be a collision, or is Brian Marsden’s 15-day margin sufficiently wide to save the planet?

  It’s anybody’s guess. As Dr. Clark Chapman of the U.S. Planetary Science Institute observes:

  Astronomers have no idea at this time as to how much the comet’s orbit will be shifted due to the disruptive forces working on the comet’s surface, which increase as it nears the Sun.54

  Such uncertainties are characteristic of the entire field of cometary research, where big surprises and big objects constantly materialize out of the darkness of deep space. Although the odds are imponderable, it should be obvious even to a schoolchild that Swift-Tuttle could go on missing Earth forever, and that another comet, perhaps one that has not been seen in our skies for thousands of years, could materialize tomorrow threatening our doom like the dragon of Revelations,

  which had seven heads and ten horns…. Its tail dragged a third of the stars from the sky and dropped them to the earth.55

  Little wonder then, when the very bright, long-tailed, long-period comet Hale-Bopp appeared ominously in 1997—making its closest approach to Earth at the spring equinox after not being seen for an estimated 4,210 years—that a sort of eschatological fever briefly seized the world. Moreover, if Hale-Bopp had hit us instead of passing us by at a distance of 200 million kilometers it really would have been the last of our days. This comet is thought to be at least twice the size of Swift-Tuttle.56

  SNEAKING UP

  Other long-period comets with orbits of 15,000 years, or 20,000 years, or 90,000 years, could theoretically appear out of the night sky at any time—without any warning. Since their previous visits are recorded in no known historical documents or traditions, we have no way of predicting when they will be coming back. The same goes for long-period comets that may have passed this way in historic or near-historic times—like Hale-Bopp in 2210 B.C.—but for which, again, no record has survived.

  Such comets, say Philip Dauber and Richard Muller, are “as likely to be orbiting the Sun opposite to Earth’s direction as with it.” When this happens,

  their potential impact speeds are even greater than those of short-period projectiles. Their usually large size—4 kilometers and up—makes them still more hazardous. These Earth-crossing comets only become visible as heat from the Sun begins vaporizing their long-frozen ices…. About a year of acceleration remains before they swing around the Sun or, rarely, collide with a planet. About half of all long-period comets are actually Earth crossers…. If we are especially unlucky, a new comet on a collision course with Earth could be detected with only two months remaining before the fatal crash.57

  David Morrison of NASA’s Ames Research Center points out that with present technology “no means exists to distinguish a faint object (either comet or asteroid) against the dense stellar background in the Milky Way.”58 He warns that it is therefore

  possible for a comet to “sneak up” on Earth, escaping detection until it is only a few weeks from impact. A perpetual survey is required to detect long-period comets, and even with such a survey we cannot be sure of success.59

  WHAT SCIENCE REALLY KNOWS

  It seems that a process of evolution is at work in the life of comets and that long-period comets gradually change their orbits through “the buildup of gravitational interactions with the major planets”60 to become intermediate-period comets and finally short-period comets with shorter and shorter orbits. So short, eventually, that they must either fall into the Sun or become enchained in the gravity of a planet. An example is Encke’s comet, an Earth crosser, which has the shortest period of all known comets—just three and one-third years—and which has been observed to become “increasingly erratic in keeping its appointments in our skies.”61 The period of its orbit is shortening fast and, as we will discover, it may be part of a larger conglomeration of cosmic debris that is presently evolving into a deadly collision hazard.62

  In the past two centuries two particularly near misses have been recorded between Earth and comets. Comet Lexell missed Earth by less than a day in June 1770,63 and comet IRAS-Araki-Alcock flew by at a distance of about 5 million kilometers in 1983.64

  When can the next close approach be expected?

  The classic work of reference on comets, to which all scientists seeking guidance on these matters automatically turn, is Brian Marsdens Catalogue of Cometary Orbits. The 1997 edition lists all of the 1,548 comets for which sufficient data exist to compute orbits—91 from the extremely scanty historical data that has come down to us from the period before the seventeenth century and the rest “from cometary passages during the last three centuries.”65

  What science really knows about comets, in other words, derives from data based on an incredibly narrow sample of cometary behavior as observed from our tiny corner of the universe in three insignificant centuries.

  FRAGMENTING GIANT COMETS

  We have seen that countless billions of comets are in the Oort cloud and the Kuiper belt, that some of these comets seem to be “spiraling down” toward the Sun—and thus toward the inner planets—and that many objects previously believed to be asteroids are in fact the remains of former comets. In a sense, therefore, it is no longer useful to think of asteroids and comets as distinctly different objects. Instead they look like the consequences of an hierarchical disintegration process in which giant comets from the outer solar system with very long orbits migrate into the inner solar system fragmenting along the way into a multitude of smaller shorter-period comets, which in turn either collide with planets—chemical tests indicate that the K/T impactor was an active comet—or manage to avoid doing so.66 Those that survive will put on ever-diminishing firework displays of dust, meteorites, and larger debris for a few thousand years before eventually becoming completely devolatilized and inert—that is, comets in asteroidal form. They do not lose their propensity to fragment, however, nor to bump into planets, and continue to cross orbits with the random danger of a game of Russian roulette.

  As we have seen, it is only since the mid-1990s that the fragmenting “giant comet” idea, which was vigorously advocated by Victor Clube and Bill Napier more than twenty years earlier, has begun to win universal favor among astronomers. The discovery of huge comets like Chiron and Hidalgo, as well as the Kuiper belt objects, has settled that. Moreover it is now clear from a study of historical records that giant comets do not always fragment in the outer solar system and can sometimes survive, more of less intact, to approach the domain of the inner planets. A notable example was comet Sarabat in 1729 that almost reached Jupiter.67 From a number of astronomical reports made at the time it is known that this comet was extremely bright—“intrinsically the brightest observed in recent centuries,” says Duncan Steel,68 that “only a ve
ry large object could have appeared so bright when so far away,”69 and that

  a lower estimate of its size is about 100 kilometers; actually it might have been up to 300 kilometers across…. It is inevitable that many similar comets on Earth-crossing orbits have arrived over geological time.70

  To this Bill Napier adds that 200-kilometer objects in chaotic orbits are inherently unstable: “It only takes a small collision to veer a comet on a path toward Earth, and who knows what it could do?”71 Such unpredictability is of course heightened by the distinct possibility that many comets may also be subject to Cape effects because of outgassing. In the case of Halley’s comet an accurate estimate of the power of these gas jets was obtained by the Giotto space probe. The jets were found to

  exert a force of about 5 million pounds, or nearly as much as all the engines of the space shuttle as it lifts off from the launch pad. And these jets continue for hour after hour, day after day.72

  MULTIPLE INDEPENDENTLY TARGETED REENTRY VEHICLES

  Since the first optical confirmation of the existence of giant comets in the Kuiper belt in 1992 no such object has yet been seen to fragment. “Ordinary” comets, however, which are intimately related to the giants in every respect, are frequently observed to break apart releasing swarms of “warheads”—like MIRVed intercontinental ballistic missiles.

  One example was comet Biela, which had a computed orbit that came “within 20,000 miles of the Earths.”73 (Although this of course does not mean that Earth and the comet were ever actually within 20,000 miles of each other; that would depend on where each of them were in their own orbits at any one time). The nineteenth-century historian Ignatius Donnelly tells the story this way:

  On the 27th day of February 1826, M. Biela, an Austrian officer … discovered a comet in the constellation of Aries, which, at that time, was seen as a small, round speck of filmy cloud. Its course was watched during the following month by M. Gambart at Marseilles and by M. Clausen at Altona, and those observers assigned to it an elliptical orbit with a period of six years and three quarters for its revolution.

  M. Damoiseau subsequently calculated its path, and announced that on its next return the comet would cross the orbit of Earth, within twenty-thousand miles of its track, but about one month before the Earth would have arrived at the same spot!

  This was shooting close to the bull’s-eye!

  He estimated that it would lose nearly ten days on its return trip, through the retarding influence of Jupiter and Saturn; but if it lost forty days instead of ten, what then?

  But the comet came up to time in 1832, and the Earth missed it by one month.

  And it returned in like fashion in 1839 and 1846. But here a surprising thing occurred. Its proximity to Earth had split it in two; each half had a head and a tail of its own; each had set up a separate government for itself; and they were whirling through space, side by side, like a couple of racehorses, about 16,000 miles apart, or about twice as wide apart as the diameter of Earth.

  In 1852, 1859, and 1866, the comet SHOULD have returned, but it did not. It was lost. It was dissipated. Its material was hanging around Earth in fragments somewhere.74

  On the last occasion, 1866, another commentator tells us that “in November, the period of Biela’s return, the world beheld a most brilliant meteor shower, and in 1872, 1885, and 1892, corresponding with its former orbit, there were imposing displays of meteors in November.75 At one site more than 160,000 shooting stars were seen in an hour and even today the debris of Comet Biela returns annually as the Andromedid meteor shower.76

  On its way into the inner solar system the Great Comet of 1744 transformed itself near the orbit of Mars into six large, luminous fragments each with its own tail from 30 to 44 degrees in length.77 On 4 October 1994, Jim Scotti of Spacewatch reported that comet Harrington—which does not cross the orbit of the Earth—had broken into at least three parts.78 In March 1976 the nucleus of comet West disintegrated into four parts.79 And we have seen how comet Shoemaker-Levy 9 broke into 21 fragments.80

  Other examples of fragmentation include comet Macholz 2, which was found by the astronomer Donald Macholz in 1994 in a region of the sky not yet covered by any of the telescopes of the world’s skeletal Spacewatch network.81 This comet is on an Earth-crossing orbit with a short period of about seven years and consists of a swarm of six individual nuclei still relatively close to one another but drifting apart—indicating that they were probably produced by the fragmentation of an original larger nucleus sometime in the 1980s.82

  The remarkable Kreutz “sun-grazing” comets—so bright that they have sometimes been seen in daylight—are a similar family of nuclei descended from a common progenitor. Consisting now of about a dozen individual objects on virtually identical orbits but with varying periods—from 500 to 1,000 years—they pass very close to the surface of the Sun, some to within just half a million kilometers of its surface.83 Indeed in 1979 one of these comets crashed directly into the Sun, being photographed just before it did so by the U.S. Navy satellite Solwind. The impact caused “a brightening over half the solar disk, which lasted a full day.”84

  Tracing back the orbits of the Kreutz sun-grazers, Victor Clube and Bill Napier conclude:

  They were once a single, gigantic object, ten or twenty thousand years ago, which underwent a hierarchy of disintegrations. There is little doubt that the tidal strain induced by the close passage to the Sun has split the parent comet into fragments.85

  We saw the effects that such fragments can have when comet S-L 9 crashed into Jupiter.86 Since any lesser planet would have been killed by those 21 hurtling projectiles, we are led to wonder whether it might not have been precisely such an incident—although perhaps on an even grander scale—that killed Mars?

  Could a gigantic comet be implicated in the dark story of the Martian past and also, perhaps, in the uncertain future of Earth?

  23

  Voyager on the Abyss

  FROM the very beginning of their great civilization the ancient Egyptians conceived of the mission and predicament of mankind as being inseparably connected to the cosmos and governed by it. They were certain that our true spiritual home was in the heavens, from whence we descended only temporarily into the material world, and that “the inhabitants of heaven” exercise a powerful influence upon our lives, which we neglect at our peril. In their teachings the stars and the planets were gods, not just remote points of light in the sky, and meteorites made of bja iron—the “divine metal”—represented an interchange between the spiritual and material realms.

  Such ideas were present from the earliest historical period and are expressed in the Pyramid Texts, the oldest-surviving scriptures of mankind. Together with the later funerary literature of the ancient Egyptians, they teach that a secret path of pure knowledge exists—“a way of ascent to the sky”1—that can lead us back to our heavenly home if we search it out and make ourselves masters of it. Nor can there be any doubt that the ultimate goal of the ancient Egyptian initiates was a form of conscious immortality—the “life of millions of years”—which would be achieved through rebirth as a star:

  O King, you are this great star, the companion of Orion who traverses the sky with Orion, who navigates the Duat with Osiris. You ascend from the east of the sky, being renewed at your due season and rejuvenated at your due time. The sky has borne you with Orion.2

  The reader will recall that the Duat sky region—the ancient Egyptian netherworld, a starry afterlife kingdom—was dominated by the constellations of Orion, Taurus, and Leo and divided by the “Winding Waterway,” which we call the Milky Way:

  The celestial portal to the horizon is opened to you, and the gods are joyful at meeting you. They take you to the sky with your soul … You have traversed the Winding Waterway as a star crossing the sea. The Duat has grasped your hand at the place where Orion is, the Bull of the Sky [Taurus] has given you his hand.3

  The Milky Way is our galaxy and the great sky river that we see is made by th
e combined light of billions of stars lying along the plane of the galactic disk.4 Within the galaxy, which is technically a “spiral galaxy,”5 all stars are indeed in motion, sailing across the Catherine wheel of spiral arms, orbiting the galactic nucleus. Our particular star, the Sun, has recently passed through the Orion spiral arm,6 so named because it contains the spectacular Orion nebula, which lies beneath the three belt stars of the constellation of Orion. Astronomers have put forward intriguing evidence that the passage was a “bumpy” one, that the solar system was severely disturbed by it and that the consequences of this disturbance have included a series of spectacular sky events during the past 20,000 years—all of them seeming to emerge from the constellation of Taurus.7

  SKY/GROUND MESSAGE

  It may not be a coincidence that the ancient Egyptians had a deep and abiding interest in the constellations of Orion and Taurus. Their belief that this area of the sky is the cosmic home to which we should strive to return is expressed not only in religious texts but also in the three great pyramids of Giza and in the so-called Bent and Red pyramids of Dashur.8 Standing at the geodetically significant location of 30 degrees north latitude (one-third of the way between the equator and the North Pole) and incorporating a series of mathematical constants, transcendental numbers (i.e., numbers not capable of extension in terms of a finite number of arithmetical operations), and geometrical ratios such as phi, pi, and e/pi, the Giza group mimic the sky image of the belt stars of Orion while the Dashur pyramids mimic the relative positions of two stars in the constellation of Taurus—Aldebaran and epsilon Tauri.9 It is likely that the Red pyramid—representing Aldebaran—was built of red stone because of the conspicuous color of its stellar counterpart, which forms “the glinting red eye” of the Taurus sky bull.10