by Vic Lloyd ©
(Investigator 44, 1995 September)
In spite of assorted social ills and injustices, and a fairly regular
spate of natural disasters, we are, as a race, an optimistic lot. We
plan ahead, blithely predict what we may expect during the next century
and anticipate — take for granted in fact — an even greater flow of
technological marvels than those we already have.
Which is not only as it should be, it is just as well because apart
from those hazards of living already mentioned, and with possible
mayhem looming in the shape of such adversities as planet-wide
pollution, the greenhouse effect and the depletion of the ozone layer,
we all live on the very brink of potential cosmic-scale destruction.
Our planet is fragile and vulnerable beyond belief and it is only the
maintenance of an exquisitely arranged system of checks and balances
that life on Earth survives at all.
Precarious as that may sound however, it doesn't end there. Lethal
radiation from a supernova as far away as say 10,000 light years could,
for instance, completely sterilise everything on Earth. And for all we
know, the leading edge of such an overwhelming wave of destruction
could well be on its way, our telescopes and instruments innocently
still informing us that all is well in the case of a given star, but
with the convulsion having occurred 9999 years ago.
Or the Sun might flare up — or cool down. Our galaxy could even become
a Seyfert, exploding and wiping out everything, out to the very limits
of its thinly populated edge. But more tenable than any of these as a
candidate for devastation is the likelihood of a collision between
Earth and an asteroid or comet nucleus.
During the first half billion years or so after the formation of the
solar system meteorite strikes on the surface of the Earth were
conmonplace. Interplanetary space was thick with debris not yet swept
up by planetary gravitation and the planets were heavily bombarded by a
deluge of cosmic missiles. Were it not for the erosive effect of
weather produced by our unique atmosphere (mostly wind and rain) the
surface of Earth would almost certainly resemble that of Mercury or the
Moon. Some authorities point to Hudson's Bay, the Sea of Japan and the
Gulf of Mexico as being possible remnants of giant meteorite craters.
But although things have improved since those perilous times there
really is no room for complacency. Less than 50,000 years ago the
meteorite that formed the Barringer Crater in Arizona generated a half
megaton blast that devastated an area with a radius of 160km. And as
recently as 1908, at Tunguska, Siberia, a million ton meteorite
levelled nearly 3000 square km of forest land with a 30 megaton
explosion sending an atmospheric shock wave twice around the Earth.
Informed opinion puts the probability of our planet becoming the victim
of a disastrous meteoritic impact as once in every 100,000 years. This
being the case we are safe for a long time to come ... but don't count
on it! Should the worst happen however, what would be the consequences?
How would we fare?
Let's conjure up a theoretical scenario and imagine a hypothetical,
1000 cubic kilometre comet, the mass of its nucleus in the order of a
trillion tons. This imaginary comet has a sideal period of 100,000
years and has reached its perihelion some 2000 times over the last 200
million years. Each encounter with the Sun has deprived it of a little
more of its volatile substance and it is now on the point of
disintegration, its rocky, dusty core held in situ only by the tenuous
grip of the final reserves of its ices and its tiny gravity.
Let us further conjecture that its next Perihelion, due next week, will
mark the comet's final journey as a cohesive whole. As it swings out
from behind the Sun on its predestined journey to the far reaches of
the solar system its ices reach exhaustion point and its nucleus
fragments into a shower of separate pieces. These vary in size from
grains as fine as flour to an awesome two-cubic-kilometre sized
boulder. This phenomenon is not unique. In 1846, comet Biela shattered,
and in 1976 Comet West broke into at least four large pieces. As a
general rule, obeying the laws of celestial mechanics, such fragments
continue to loosely cling together and travel the comet's orbit as an
That is, unless it falls under the influence of external forces. And
with our fictitious comet, such is the ease. By coincidence, Mercury,
Venus and Earth are in alignment with the Sun and the trajectory of the
clump carries it on a path which just grazes the outer limits of the
gravitational fields of the inner two planets. Not enough force is
exerted to drag the whole cluster of fragments to their respective
surfaces, but it is sufficient to attract the largest segment, the
two-cubic-kilometre-flying-mountain (which, to provide an
identification we shall now call 'Azar'). Nevertheless, the immense
boulder bypasses both inner planets, missing them by a few thousand
kilometres in each case. Travelling at almost 50km per second Azar is
now on a collision course with Earth.
What happens next is a bewildering and appalling series of events. As
Azar hurtles past Venus, astronomers calculate its velocity and plot
its course, verifying at once that it will certainly strike the surface
of Earth within the next few days. However, it is impossible either to
establish a precise impact point, or take any practical measure
designed to alleviate what is obviously going to be a disaster of
monumental proportions. World authorities are warned accordingly.
A land strike would be catastrophic enough, especially if a heavily
populated area were involved, but in this event most of the energy
generated would be radiated back into space fairly quickly. However, an
ocean strike would have much more serious and far-reaching effects
Azar, which has a mass of two thousand million tonnes, powered now by
Earth's gravitational pull, builds its velocity to 80kps. It is in
Earth's lower atmosphere for only two seconds and punches through the
final 20km of ever-increasingly dense air resistance in a blink of the
As it slams Earthward an immense air-cushion forms as a bow wave, so
compressed that it turns to plasma, a boiling, turbulent slush of
ruptured, collapsed oxygen and hydrogen atoms, their abandoned
electrons glowing with the vivid blue of hard radiation. The massive
air-cushion has no discernible effect on Azar's velocity and in that
brief moment, generating immense heat and light, it glows like a
dazzling little white dwarf star brighter than the Sun, imprinting a
burning track of abused electrons in its wake.
As air rushes in to equalise the near vacuum left by the incandescent
trail a thunderclap louder than anything heard on Earth for millions of
years radiates out with murderous intensity, producing vibrations
violent enough to powder stone. Any animals or people engulfed within
the influence of its terrible resonance simply disintegrate.
Reaching the surface, and now glowing at 1000 C , Azar punches into the
South West pacific Basin, 800km south of Tonga. There is no splash.
Subjected to the brutal velocity of the immense boulder — nearly
300,000 kph — water has no more resistance than air. In a millisecond a
vast area of ocean is vaporised and Azar plunges deep into levels where
darkness has been the norm for thousands of millennia. It penetrates
half a kilometre of seabed sediment and 5km of crust 1ike a hot knife
through butter, finally coming to rest in the dense Mohorovicic
Discontinuity, eleven kilometres beneath the surface of the ocean. The
unparalleled force of the impact shatters rocks to talcum powder for
hundreds of square kilometres around and releases a savage gush of
No point on Earth escapes the devastating shock effect of the ferocious
collision. The tectonic plates react to the outrage by tilting and
buckling as a pulsating wave of energy ripples through them. Buildings
topple, dams burst, bridges collapse and whole sides of mountains
detach and thunder down valleys. In the United States and Europe,
several nuclear power stations are demolished with frightening
consequences. The abrupt cessation of Azar's colossal momentum has
released energy equivalent to that of 600 thousand megatons of
exploding TNT. Even at this early stage in the chain of events the
turmoil is unprecedented and the toll of human life horrendous.
Meanwhile, at the site of the impact a gigantic crater, five kilometres
deep and fifty kilometres across, opens for a fraction of a second. In
that instant, 10,000 cubic kilometres of water (enough to cover the
whole of Australia to a depth of 6.5 metres) is transformed into
superheated steam, as clear as air. Behind the steam, forcing it
upward, a gigantic fireball surges to the surface, expanding and
spreading across the ocean at 1000 kph.
Momentarily, a circular wall of water hovers three kilometres above and
around the vast oceanic crater and then, in a flood more terrifying
than anything ever seen or heard, roars back into the abyss — in turn
be to instantly vaporised into millions more tons of steam as the water
hits molten lava at the crater's base. Nothing within an area of 1000
square kilomtres survives the onslaught and nearly all of the pacific
islands vanish for ever.
As the scalding vapour shoots skywards, bearing an assortment of
debris, mountain ranges of dense cloud build up, kilometres thick, and
promptly begin to spread around the globe. Winds reach hurricane force
in response to rapidly changing atmospheric pressures and lightning,
accompanied by ear-splitting thunder is constant as electrical
potential builds and discharges in wild confusion. The whole planet is
soon deluged by torrential rain as the massive clouds reach into the
upper atmosphere and precipitate.
On the surface of the ocean, even more mischief is afoot. Forming a
circle around the impact point a wave, already ominously higher than
those associated with known tsunamis, speeds outwards at 1200 kph. When
it reaches the continental shelves of the land masses surrounding the
Pacific Basin it begins to build until, when it strikes the coastal
shal1ows, its wavelength shortening, it becomes a towering mass of
energy filled water, 700 metres in height (as high as Mount Lofty).
With terrible force it sweeps away whole cities, races up rivers and
causes enormous destruction as it smashes inland, its energy only
expending when it reaches high ground. And, as it sweeps back into the
ocean with almost as much speed and vigour the water carries millions
of tons of detritus and the bodies of uncountable people, clotting the
seaways on an unprecedented scale.
Although the coasts of the Pacific countries bear the initial brunt of
Azar's brutal assault, the whole planet is cruelly afflicted in the
long term. Rain, on a world-wide basis will be incessant for months to
come, bringing with it millions of tons of oceanic ooze, salt and
pulverised rock, poisoning topsoil everywhere. And the kilometres thick
cloud mass, temporarily rivalling that of Venus, will not only block
out the Sun, its upper surface will reflect sunlight and therefore
heat, back into space. Our ecological pattern will change radically;
some lifeforms disappearing for ever and others proliferating. Most
deserts will vanish to be replaced by barren, soggy marshes; the polar
caps will increase in size and in the northern hemisphere new gigantic
glaciers will slowly encroach into the continents. A new ice age is not
an unreasonable assumption. It could well take a thousand years for
Earth to fully recover from such an ecological outrage but in some
areas things will never be the same. In order to survive, especially in
food production man's ingenuity will be stretched to the very limit...
A11 of this is, of course, only a hypothetical scenario; a pretty piece
of imaginative 'science fiction' based on theoretical possibilities.
However, Asteroid 1991 BA ('the size of a small house') came perilously
close to producing something 1ike the foregoing in January 1991; it
missed us by a mere 170,000 km. Moving at about 50km per second the
Asteroid was less than an hour's travelling time away. A tiny
adjustment in its trajectory might have made an enormous difference to
our wel1-being; we only narrowly escaped what could well have been a
But what about its next orbit...?