Asteroid Impacts - Danger, or Opportunity?
by Dr. Michael Martin-Smith
In a recent edition of "Le Scienze" (italian edition of Scientific American), there appeared an article by Mr. Aldo Conti on the subject of the risks- if any - posed to Earth by collision with asteroids or comets. I hope I am fair to Mr Conti when I summarise his view as follows:
I know this is a crude summary of Mr Conti's views, but I believe it to be correct. I fear that there are a few oversimplifications in this analysis, and that, most importantly of all, the point that Near Earth Objects represent a gigantic opportunity for an adventurous and restless species has been missed. Indeed, of all the hazards which face our species, the Impact Threat is the only one which can be used to increase our wealth and potential beyond all imagining! It is now recognised that there are 10 or more potential colliders of 5 kilometers diameter or more; since an impact by one of these comes with 20 Teratons ( 20,000,000,000,000) of kinetic energy, equal to 10,000 times the energy of all our nuclear weapons, it is obvious that our civilization, and probably our species, would not survive. In general, such an encounter is now expected every 10 million years or so - although, these events are not regular and predictable. It could happen next century, or in 20,000 AD - who knows? An impactor of 1-1.5 kilometres is now, from extensive modellings, believed to be sufficient to cause global climatic changes which our fragile civilization could not survive.
Apart from shock, earthquake waves, 1000 kph winds, fireballs ( 2-3000 kilometres across, 24,000 degrees Kelvin, were observed in 1994 at Jupiter), one must think of secondary effects - epidemics, breakdown of civil order, pests, rupture of nuclear waste containers and much else. The damage would be the loss of 5 billion people and several trillion dollars' destruction. Such an impact can be expected at 1-2 million years intervals, remembering that we do not know when the last one was! Recent work in America and Australia finds 450 impact craters of 100 kilometers or above over the past 3.8 billion year many of them into the sea. Marine impacts, dismissed as unimportant, produce a wave( tsunami) usually equal in height to the diameter of the impacting body. Thus a 300 meters object ( of which 2 have passed within Earth - Moon distance in the past 9 years, while two more were found this summer!), would raise a tsunami 300 metres high at impact, falling off to 240 metres at 1000 kilometres distance. height falls off simply, so that at 2,000 kilometres wave height is 120 metre high, while at 6,000 kilometres from impact, the tsunami is still 40 metres high. We do not have to imagine the effects of such an event; a submarine earthquake at Papua New Guinea, this summer, showed us what a 10 metres wave can do - kill 3,000 and destroy much of the local infrastructure. A 300 metres object impacting ANYWHERE in the Pacific would thus send 40 metres or larger tsunamis to every city on the Pacific Rim. 25% of the population would be killed, and the loss of property would exceed a trillion dollars. The collapse of the world economy and spread of global epidemics would be small parts of a very nasty picture. An impact of this size can be expected every 100,000 years or so - well within the likely lifespan of human civilization. Our civilization is, contrary to normal expectation, more vulnerable than a simple society, because there are more people and structures available for destruction, and our civilization is so interlinked. At present, we have no idea how real this threat is, because we have knowledge of at best only 10% of the thousands of potential objects. Indeed, new Comets from the Oort Cloud, and asteroids falling into the Aten, or more recently discovered Tholen groups, spending all or most or their orbits between Earth and Sun, are virtually undetectable by present methods. The world wide Spaceguard Organization has shown that 6 dedicated 2 metre class telescopes, at a cost of 20 million dollars worldwide, could find 90% of potential hazards within 10 years. This would at least give us an indication if there is an immediate threat. However, there are two points to make. Small asteroids and comets, once located, can go missing. They are subject to minute gravitational tugs of war between nearby planets, and also from rocket effects produced by ejected volatiles as they approach the Sun. Thus a search should include continual logging and tracking. New Long period comets are of their nature unpredictable until discovered - Hale Bopp was found only 21 months before its closest passage, and was a large one. Hyakutake was found with only 3 months' warning, and would beyond doubt have destroyed us if it had impacted.
All right then, we have shown that there is a certainty of eventual destruction of civilization, and possibly all human Life, at an unknown date in the future which could lie years, decades, or millennia in the future. At this point, we must ask "Are we humans, with Minds and Intelligence, or are we a rather nasty form of carnivorous Ape?" If you believe the latter, read no more - there is nothing which can or should be done. But the species which produced Leonardo da Vinci, Einstein, Jesus, and the exploration of our solar system, with mathematical theories of the Universe reaching back almost to the very Beginning of Time, surely has more to say than "So what?" Possible countermeasures include nuclear-tipped missiles, lasers, mass drivers. To apply these we must learn much more about the make-up of possible targets; indeed, studies from the NEAR spacecraft of the asteroid Mathilde suggest that an explosive attack would either do nothing, or simply give us two objects instead of one. So the next stage must include a small asteroid lander/sampler mission , perhaps one per year, for the indefinite future, to gain local information. These can now be done for 120 million dollars per year, while in 2001, a private entrepreneur, Jim Benson, of SpaceDev, aims to send a craft to Asteroid Nereus , funded commercially by selling of payload capacity on his vehicle, and by sale of data . This mission ( Near Earth Asteroid Prospector) is expected to cost 50 millions complete, and to make a profit. We can see that the first requirements for an intelligent, human proactive response to this threat are already clear, and easily affordable. 100 million dollars per year for 6 billion people is a far lower premium than you or I pay for house insurance! Lasers could be used to heat up one side of a body, induce outgassing, and thus slightly deflect its orbit out of harm' way. However, the Lasers must be emplaced off the Earth to avoid the dispersing effects of our atmosphere, and there must be many years' warning . The Moon, with its newly discovered assets of 10 billions of tons of water ice) is an obvious candidate. Another approach is for a crewed spacecraft to visit the asteroid , and there emplace either a thin silver foil for solar pressure radiation, or an electric mass driver catapult to slowly nudge it into a safer path. It is clear from the above that, if we are to reliably protect our descendants from annihilation by incoming asteroids or comets, we must build up a presence in Space powerful enough to detect, assay, and deflect such bodies in good time.
At this point, I propose that we look at the question in a totally new way. These asteroids and comets are not made out of thin air- they contain billions of tons of the raw materials of civilization, bathed in solar energy billions of times more copious than is ever utilized by our small fragile Blue planet. If we must live in an ecological system which is larger than the Earth - as this whole story demonstrates, then, the lesson is clear; we must reach out into Space. Let us utilize these self-same resources to build up a Greater Earth - a Civilization in which all the resources within our gravitational field are consciously and deliberately used to build a cosmic civilization. Humaity can now learn, like the Jews of past centuries, that, in a dangerous and threatening world, two factors make for survival and development - Diaspora, and an unshakeable belief in a future Destiny. Of all the creatures which have ever lived on Earth, we alone have the power to take Life and Mind out into the wider Universe, and transform ourselves and the Galaxy in the process. It is for this, our Cosmic Destiny, for which our Minds, with their restless, pioneering curiosity, were called into being. Just as, 350-400 million years ago, our marine ancestors for whatever reasons, moved out into the harsh and hostile realm of Terra Firma with lungs and limbs as new tools, so, too, with our intelligence, social co-operation, science and technology, we must move out, on pain of death, into the larger cosmic Ocean before us! The Asteroid Threat is thus Nature's way of telling us to grow up and reach beyond the "Womb Planet"