“The fault, dear Brutus, is not in our stars but in ourselves that we are underlings”

So wrote Shakespeare in Julius Caesar.

That being the case, can we in this age of science attribute the strange occurrence of biological phenomena on the Earth to external forces, such as the erratic behaviour of a star, out there in space for want of any other plausible theory.

As the eminent science writer Timothy Ferris points out, that at various times during the long history of our Planet, millions of species, that had been getting along well, have suddenly died out enmasse. These biological extinctions appear to have occurred periodically at approximately intervals of 26 million years. Evidence gathered by scientists in America suggests that they were triggered off by something from beyond the earth. Could it have been such a star?

A few decades ago two geologists of Princeton Uni­versity observed that extinctions of sea life occurred in cycles one every 32 millions years or so. Similarly two paleontologists who had compiled records of the rise and fall of 3500 families of marine animals noticed on the basis of computer analysis, 12 major extinction events that fit a 26-million year cycle. They began to speculate that the ‘die offs’ might be related to extraterrestrial forces.

But the question arose as to what exactly those ‘forces’ were. Some Scientists are beginning to believe that a comet could have done the deed, by striking the earth, and clouding the atmosphere with debris, plunging the planet into a frosty, winter, to which many of the most exquisitely evolved creatures could not adapt in time to survive. Even a chunk of stone 16 kilometres in diameter hitting the Earth, at a velocity of 16000 kilometres per hour, would explode with a force equal to  10000 times that of all the deliverable nuclear warheads in the world. Hence the killer comet need not have been large.

Such comets are believed to originate in the “Oort cloud” where about 100 billion comets lazily and calmly circle the sun as dray oxen do in a field. A massive body passing near the solar system could shake millions of comets loose from the Oort cloud sending them skidding down into the inner solar system where some would surely hit our planet.

But even if we assume that comets from the Oort cloud may occasionally bombard the earth, why should they do so at periodic intervals? Ferris refers to two theories that have been put forth in recent years. One theory holds black clouds in space responsible. Another theory suggests that the sun is visited periodically by a hypothetical ‘companion star’, indicated above. Its proponents have named the star ‘Nemesis’ (after the Greek Goddess of retributive justice). They believe that this star circles the sun in an orbit several hundred thousand times farther away than that of Earth. On its closest approach once every 26 or 30 to 32 million years, depending on who does the calculations, its gravity shakes comets loose from the Oort Cloud, into the inner solar system. The four American scientists who had proposed the Nemesis model believe that three or four comets would hit the Earth, every time this star came close, and that the Nemesis model would explain available facts. (This would mean that our sun is a double star, its companion being a dim dwarf travelling in a highly elliptical orbit). There was, according to eminent science writer Michael D Lemonick, evidence in the fossil record of a massive object having hit the earth at around the same time the dinosaurs disappeared about 65 million years ago. There was an apparent 26 million cycles in the periodic mass extinctions of families of organisms over the past 250 millions years. There also seemed to be a similar periodicity in ages of very large impact Craters on Earth’s surface.

The Black Cloud theory suggested by two American scientists envisions the solar system periodically passing through regions of stormy galactic weather. Many dark clouds of dust and gas lie along the plane of the Milky Way galaxy — the vast disc, shaped something like a phonograph record in which reside the sun and 100 billion other stars. As the sun orbits the centre of the galaxy, it oscillates vertically like a needle slowly bobbing up and down on a warped record. These oscillations carry the solar system through the galactic plane every 33 million years. Some interstellar clouds may be massive enough to shake the clouds out of their perch in the Oort cloud triggering off a cometary bombardment of the Earth and the other planets.

On the Earth’s surface scores of Craters, which may be regarded as the scars of old meteor and comet impacts, have been located and age dated using methods based on radio activity. One Geologist compiled data on more than 80 impact Craters. The two scientists who devised the Black Cloud theory analysed the data on 41 of them and found that the Earth had been peppered with Craters every 31 million years. Reanalysing the data gathered by the two paleontologists mentioned ear­lier they found the mass extinctions too may fit a cycle of roughly 30 million years. Similarly two scientists, belonging to the team that had suggested the Nemesis model, carried out a study of 13 impact Craters and came up with a period of 28.4 millions years. So it just might mean that the solar system weathers interstellar storms when it passes through the clouds of the galactic dust, and that billions of Earthly creatures perish in these storms.

Lemonick opines that on closer inspection however, both theories seem to have a few drawbacks. The major trouble with the Nemesis hypothesis is that no companion star to the sun has yet been located though astronomers have been searching for one. (Numerous black dwarfs, brown dwarfs and other incon­spicuous stars are adrift in the solar neighbourhood undetec­ted, due to the limitations of present day telescopes, but it is possible that one of these stars may be orbiting the sun). Astronomers are all the same regularly scanning the skies, and analysing the data gathered by the now defunct infrared Astronomical Satellite. If Nemesis (the hypothetical star) does exist there is a good chance it will be found within the next decade. But calcula­tions show that a companion star orbiting as far from the sun as Nemesis, would be disturbed by molecular clouds and passing stars alike. It simply could not remain in a stable orbit for the required millions of years. One of the scientists who advocate the Nemesis theory counters this argument with calculations that allow for a steady orbital decay moving Nemesis away from the sun over eons of time. Such mathematical jugglery makes the theory too contrived for others to accept its credibility.

The major drawback of the Black cloud theory is that nobody is quite sure just how interstellar clouds are distributed along the galactic disc. Though our solar system may indeed cross the exact beltline of the galactic disc only once every 30 million years, it spends nearly all its time somewhere in the disc–the Sun climbs out of the disc only for the same duration, relatively speaking, as a dolphin spends jumping out of the sea and the disc is full of clouds. The proponents of the Black Cloud theory contend that this may not matter, as in their view the dense clouds, that would do the best job of jarring the comets loose, are more or less concentrated along the beltline, while the clouds that lie far away from the beltline tend to be less dense and therefore less able to influence the comets.

As Ferris observes mass extinctions do not come with clock like regularity, but often fall a few million years to one side or the other of the cyclic time. This is one reason why some researchers come up with a period of 30, others with a 26 or 28 millions years. The ‘Nemesis theory‘ attributes this variation in the data to the inherent randomness in the amount of time the Earth may take to make its way in a comet infested solar system, before ploughing into a comet. The black cloud theory points out that interstellar clouds are randomly scattered along the galactic plane. Our dating of fossil ages is accurate for only about the last 150 millions years. Before that its a bit crummy. In any case some scientists are of the view that dinosaurs did not all die out within a few years—their numbers were in significant decline for a long time, a theory that is disputed by other scientists who attribute their extinction to the violent impact of  a massive  asteroid.

Indeed the sun lies close to the galactic beltline now. Yet the interstellar space surrounding us is remarkably clear. The reason is that we happen to be passing through a giant bubble swept clean by the recent explosion of a star. So it seems we are in for clear sailing for a while.

Recently, according to Lemonick, yet another extinction from-space theory has gained currency. Astronomers still find it difficult to explain certain irregularities in Neptunes orbit that led to the discovery of Pluto in 1930s, but which Pluto is too small to account for. The real cause according to them well may turn out to be the mysterious Planex X a body one to five Earth masses, 15 billion kms from the sun (twice as far out as Pluto at its farthest).

The Caltech scientists, who postulated its existence conjecture that Planet X may have a mass about 10 times that of Earth and be similar in size to Uranus or Neptune. The predicted orbit is about 20 times farther from our Sun on average than Neptune (which orbits the Sun at an average distance of 2.8 billion miles). If such a planet exists and if a close-in mini-Oort cloud also exists then, regular, periodic massive deaths on our planet may yet be a real effect vindicating the perversely romantic theory of Nemesis, the ‘death star’ in an indirect manner. American scientists, how­ever, have not yet found evidence to indicate that there is in existence such a tenth planet in the solar systems. The search continues.


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