Comets are larger, faster, and more numerous than Asteroids, and more unpredictable
Asteroids have always frightened us. They are rocky, they are near, in the asteroid belt between Mars and Jupiter, and they are numerous. However, Comets may be even more dangerous, more numerous, faster, more unstable, and substantially larger.
Today we live in a great world interconnected by vast networks of electromagnetic communications which order our civilization into a vast complex of multi-level existence. We might say that as a world species, we are an organism, even if at times, we seem to attack our own. Today we have achieved the highest level of not only human existence, but of any living existence that we are aware of. Never before has a living organism reached the level of evolution that we have. In all ways, no matter the ultimate impact on the rest of the Earth, the human organism as a whole is quite exquisite, quite beautiful.
Yet, despite our advanced technology, despite our advanced weapons, despite our mastery of today’s technology, our civilization is not beyond the possibility of a sudden, and irrevocable termination. There are a number of possible scenarios which can result in our end. A few are simply unavoidable, as for example a volcanic episode of some kind, or perhaps a very severe climate change, or perhaps an astronomical event of some kind. Yet this last category does have one possible remedy if it is of a specific kind. If the destructive event had to do with an asteroid, or comet, there might indeed be a chance to avoid absolute destruction.
We have all heard of the Dinosaur extinction 65 million years ago. We have all heard that a very large asteroid, possibly as large as six or seven miles across hit the Earth and caused enormous and widespread destruction all over the planet and putting an end to the reign of the Dinosaur. The destroyer was supposed to be an asteroid possibly dislodged from what is known as the Asteroid belt, which lies between Mars and Jupiter, by some collision or gravitational perturbation in space. Once dislodged the Asteroid is supposed to have hit the Earth and created a huge impact crater at Chicxulub, in what is now Mexico and the Gulf of Mexico, being only a few miles from famous Cancun. But was the culprit an asteroid? Or was it quite possibly something else? Was it a comet instead?
Asteroids tend away from Earth, Comets tend toward it
Although asteroids are quite numerous, and quite near by comparison, tend to be much smaller than the largest comets and they also tend also to be slower than comets. Due to their nearness they simply do not have as much time, or gravitational fetch, to accelerate as fast as would comets which originate from much further away. Beyond this, Asteroids tend in fact to be more stationary once in orbit than are Comets because they are usually made of rocky, or metallic material, where Comets are usually made of Ice and Dust. This ice will often melt once it comes into close orbit around the Sun, and this often tends to result in explosive propulsion which gives the Comet the ability to actually change direction and orbit and thus in theory at least able to cover more target area than an Asteroid.
Moreover, the Asteroid belt is stewarded by the giant planet Jupiter, whose powerful gravitational field will tend to pull the asteroids away from the Sun and Earth and out closer to itself. Comets however tend to encounter the very opposite effect from Jupiter in that if ever they should pass close to Jupiter in their history, they will tend to be drawn towards the Sun and Earth. This same would apply with encounters they may have with the other giant planet, Saturn, as well. Thus any comet coming close enough to Jupiter or Saturn will actually tend to come nearer to the Earth and present an even greater danger. Even Neptune and Uranus are in some ways large enough to have this effect, though to a lesser degree than the giant planets Jupiter and Saturn, being that they are substantially smaller, though still four times as large as Earth.
Kuiper belt objects
There are two gigantic breeding grounds for Comets in the Solar System. The first, known as the Kuiper belt, is a large tube like region around the Sun, beyond the orbit of the planet Neptune. This region is quite extensive and may reach as far or more than 50 astronomical units (au) which are each equal to the distance between the Earth and Sun. That is a very great distance away but there are possibly many hundreds of billions of these objects out there and some are quite large, with unstable orbits.
A few of these objects are nearly as large as the former planet Pluto which by the way is also a kuiper belt object itself. Years ago Pluto was designated as a planet, or the ninth planet of the Solar System, but it has since been demoted to a so called Trans-Neptunian Object because it’s orbit extends beyond Neptune. However, whatever these designations are worth, the reality is that there are many other Trans-Neptunian objects in the Kuiper belt, and though none so far have been found to be as large as Pluto, many are nearly as large. In the past twenty years, hundreds of very large objects have been found to exist in the kuiper belt orbiting around the Sun, and by some estimates there are at least 70,000 objects with a diameter larger than 100 kilometers in the Kuiper belt.
This is somewhat disconcerting. The truth is that many of these objects do not really have stable orbits at all no matter what anyone might say. Any of these small planetoids can easily be swayed by the Giant planets in our solar system, like Neptune, or Uranus, or Saturn, or Jupiter, or can even collide with one another and take a very different path than the one they are on now. The Kuiper belt in not as gravitationally stable as are the lower orbits around the Sun, and thus it does not take all that much to move an object in the direction of the Sun, even a very large object from orbit. Any small collision, or any gravitational nudge can conceivably send a very large object into the gravitational field of the Sun and thus cause it to accelerate towards Earth.
The possibility always exists that one day we may wake up and find that a number of very large objects are heading towards Earth orbit. It is quite possible that a single disturbance can result in the breakup of a large object into smaller but deadly comets and head towards the inner Solar System as they make a b-line towards the Sun. Many would say that this is nothing more than an another foolish end of the world scenario that never happened, or never will. But when we look very carefully at the facts we can see that these things not only can happen, but almost without question have happened before!
Oort cloud objects
There is a region beyond the Kuiper belt, that is even larger and more extensive, and even more gravitationally unstable. Though much further away, the gigantic Oort cloud , named after Jan Oort, the Dutch Astronomer who is credited with its discovery, is the probable well source of all objects in the Kuiper belt. This region is spherical and exists at the very edge of our solar system. It is huge, and contains trillions of objects and is where most long period comets originate from. The theory is that it is a leftover from the formation of the Solar System billions of years ago. Objects in the Oort cloud are so far away from the Sun, that they are barely subject to the Sun’s gravitational pull, and thus are at all times more prone to extreme deviations even after small changes in the overall field. For example even a nearby encounter with a star can perhaps cause objects in the Oort cloud to change their orbital direction, sometimes towards the Sun and Earth.
There are two types of comet orbit designations. One is a short period comet which comes from the Kuiper belt. These tend to show up periodically, like Halley’s comet for example. They go around the Sun, then head back out to the Solar System’s outer limits, only to return in a few decades.
Long period comets are comets that tend to have exceedingly long period orbits and originate in the Oort cloud. These can have an orbital period as long as 50,000 years! That is to say we might be due to see a comet appear for the first time in human history that originally started its journey some 25,000 years ago! Indeed, this object might not only appear on the horizon on any given day, it could be heading for Earth, and it could be gigantic. In fact it could be much larger than the asteroid commonly supposed to have killed off the Dinosaurs; that is often quoted as six miles across, but some Trans-Neptunian Objects can easily be hundreds of miles of across.
Earth strikes happen often
The incidence of comet strikes on Earth are actually quite numerous. Most are tiny and we hardly notice. Others, larger tend to make themselves known. However, though relatively rare, they happen, and they may well happen in streaks. This last statement should not be taken lightly. The reason may be that one general perturbation may be responsible for dislodging a number of comets from their orbit at once. We may not simply see one comet get close to Earth, there may be a number of these all at once. The same goes for asteroids, as they too can happen in streaks. Indeed the last few sightings have seemingly come together in multiple occurrences.
The most recent of these, the meteor that struck Russia’s Chelyabinsk region, is said to have disintegrated in the atmosphere, just like one such comet or asteroid did in 1909, the famous Tunguska event in Siberia. Yet, though they disintegrated in air, their blasts were formidable causing quite a bit of damage. If not for a few accidentals, like for example the fact that these regions are quite isolated, we might well have been looking at a horrendous tragedy of unheralded proportions.
More often than not objects that strike the Earth are most often said to be asteroids, but many actually turn out to be comets. The fact is that comets are far more likely to blow up in the atmosphere than asteroids. It actually turns out that the last event at Chelyabinsk really was an asteroid because particles were subsequently found which as far as we know designated it as an actual asteroid. But the Tunguska event, which was much more powerful and destructive, left no crater and no particles. And many now believe it was indeed a comet that disintegrated in air before actually striking the Earth. Yet the shock wave was large enough to flatten trees for miles around.
Comets can get awfully large and cause an awful amount of destruction. Potentially, due to both size and speed, they can actually cause far superior destruction than the greatest of asteroids. They are also probably far more numerous, and worst of all, they are far less easy to detect. As we have said before they tend to be made of ice and so will be subject to melting as they approach the Sun. This can cause the explosive release of gas within the comet and change its orbit. Thus they are not only hard to predict because they come from so far away, they are also inherently unpredictable due to the material they are made from. Yet they are both numerous, and potentially extremely destructive and are well known to appear from time to time.
We can of course say that comet or asteroid strikes are only a matter of luck. True, these are a matter of luck, but mostly bad luck. The Earth has gone four billion years without a life ending comet blast. A sufficiently large comet like the ones we are referring to here, nearing 100 kilometers in diameter are not survivable. It is quite unlikely that any life at all is going to survive, not even sea life, should an object that large get past the Moon and strike Earth at full speed. And yet there are billions of these objects out there! Any one of those objects might have begun its trip towards our planet thousands of years ago, and we would not detect it if it is under planetoid size especially since these things tend to have what are called eccentric orbits that do not adhere to what is called the ecliptic, or the usual orbit of planets around the Sun. Therefore, these comets, especially those long period comets originating in the Oort cloud might actually come from the direction of the poles where there is very little monitoring since there are so few people watching. We may not discover such a body or group of bodies till they are only a few months away. Should that happen now, we would probably have to endure an agonizing few months of utter social degeneration before the final, ghastly cataclysm, a nightmare greater than any we can imagine, or authentically describe.
So What do we do about this?
So what should we do about this admittedly unlikely event? Well first let us consider if it is really all that unlikely. We have not seen evidence that a very large comet has struck Earth because if it did, we probably wouldn’t be here at all. It would have wiped out all life in all probability. But if in four billion years it has not happened, and the possibility has existed that long, could we say possibly that such a terrible event might be well overdue? Do we know? Truth is we really honestly do not know what the true odds are here because we don’t as yet know how many such objects there really are out there, and just how often do they tend to drop in for a visit. Remember we have only been monitoring the skies for a few thousand years, these objects may take hundreds of thousands of years to appear, or millions even. Thus they may in the distant past have come close quite often, we were simply not here to see them. That is an awfully scary notion when you think about it. Yes, it is obviously somewhat annoying to consider such an unlikely event and try to make it a possibility, as we are sure many of you might be thinking by now. Why stir up such unlikely scenarios anyway with so much more pressing matters to think of? Yet the reality is that in this particular case we really don’t know how unlikely it is, or is not. We have had a spate of near misses in the past few years. Are they getting more numerous?
Consider the event recently where the Chelyabinsk meteor strike actually happened while another asteroid, larger that it, was scheduled to just miss Earth, and thankfully it did! But it was a terrible shock to hear that on that very same day when one asteroid missed us, another hit us! On the day we were struck, two asteroids were gunning for our planet at the same time! There is at least some small reason to consider that these things are not as farfetched as we might believe.
We are learning that in the past the Earth has been struck by meteors of varying size and destructive power many times. But apparently not by a terminal body of very large dimensions, though we know now that they do exist, and can potentially head our way. Yet after four billion years, perhaps we should consider it as a possibility.
Comet Shoemaker-Levy left no doubt, comets can strike planets
A few years ago we witnessed the comet Shoemaker-Levy strike Jupiter. It was a large comet, approximately six miles in diameter, and the damage done was tremendous. Had it struck the Earth, you would probably not be reading this, and I would not be writing. Astronomers were dazzled by its force and power, but they were also surprised by the fact that it had broken up into smaller pieces by Jupiter’s enormously powerful gravitational field, yet still managed to do a great deal of damage. Had it hit Earth, it probably would not have broken up at all and would have hit us in one piece and some things very ugly and sad would have been left behind. But we needed no more proof that these things really do happen. Those comets are out there. They are real. They can become our most horrific nightmare any day or night. They can destroy us, and everything we have ever known of, or ever loved on Earth.
But again, what should we do? Is there a good enough reason to begin to develop counter measures? Considering costs, and so many other problems should we even bother with such a small, purely random event? Are there any sound reasons to proceed to some sort of genuine planetary defense against such rare, if albeit destructive occurrences?
We think there are. In the end, we do have the technology. Yes it will be expensive, admittedly, but the technology is there. We can build a specific kind of rocket, or possibly even lasers that would be able to significantly deflect or destroy a reasonably sized body. No it could not probably protect us from a planetoid, but we could probably protect our world from what might be smaller bodies which are after all far more numerous and so perhaps more dangerous when taken altogether. There is a general consensus that such a system could be built in earnest if we really wanted to build it. Even if it meant nuclear tipping a rocket, consider what we are talking about. Consider carefully what it would mean if suddenly we discovered a very large comet was heading towards us, or a group of such comets. Consider what this might be like to live the last few months in sheer agony and regret for not having taken steps to prevent it. Having some option would certainly be desirable. But without actually building such a system, and testing it years in advance, it could never become operational in the few months to a year that we might have warning. This is why it is perhaps time to consider building a defense system against either asteroids, or comets. To save all life on Earth is no small feat, nor is it mean, or ignoble when you really think about it. After so many billions of years, our time may be running out. The planet Earth has given us everything we have. She has nurtured, protected and sustained life for four billion years, perhaps now is the time for life to do the same for her, our one common mother. Perhaps it is in some way a duty to consider.
A Post Script : The End of the World Hypothesis
A post script is in order. Recently a theory published by an astronomer Michael Rampino, warned of the potential for a mass extinction as the galactic planes lines up with the Kuiper belt during the age of Aquarius, and possibly begins to knock some of these Trans Neptunian objects towards Earth; being that their orbits tend to be unstable and easily changeable through the action of the galactic core gravitational force. He named this the “Shiva” hypothesis, Shiva being the Hindu Goddess of destruction. Though we do not honestly know that this hypothesis is all that likely, who’s to know in the end? To be sure, the Maya predicted this age would be the end of ages, and this is a new age as the Sun enters a new astrological configuration in the heavens. And it is true that indeed the Solar System is actually lining up with the galactic core plane during this coming age. We don’t know in the end what truth, or lack of there may be in these events as causes for a new wave of extinctions, as the Shiva hypothesis proposes. However, what we do know is that these icy , distant, dark objects really are out there, they visit us often, and have caused massive destruction in the past, and but only a few years ago on Jupiter. Thus far our lovely planet has escaped the worst of it, but its time may be running out. We may be overdue for some such occurrence. Perhaps it is time to consider in earnest taking an insurance policy against the very worst that can happen. It would be a shame to lose it all now, wouldn’t it?
See Shiva Hypothesis
also Comet Siding Spring