Jack Oughton Astronomy, Eschatology and Apocalypse: Threats From Space

In the last century, the advance of human technology and industry has come far enough that we can now, for the first time, threaten our own existence. But the continuing survival of humanity is not dependent entirely upon our actions alone. There has always been, and will always be, however small the chances are of occurrence, natural catastrophes with differing damage potentials, from threatening small areas, to life itself. Planet earth is more resilient than humanity, and has weathered countless events that if happening today, would annihilate all creatures on the planet. But as scientific understanding grows, so does our awareness of scenarios that threaten the continued existence of our tough planet. It goes without saying that the chances of most of these scenarios actually happening are so remote as to be nearly impossible, and many of the solutions offered aren’t even close to technologically viable within the near future. However it would be foolish to discount such scenarios and solutions, nobody can predict the future.

Threats of Human OriginNUCLEAR EXCHANGE CAUSED BY MISINTERPRETATION OF ASTEROID AIRBURSTSThe stockpiling of nuclear weaponry since the mid 1940s has given the fragmented tribes of humanity the tools to utterly destroy each other. In the 1960s, the Cuban Missile Crisis was an example of two tribes almost ready to ruin the world. Although today the threat of nuclear war has diminished, similar nuclear stalemates still exist, as many major countries possess these weapons. An example of this is between India and Pakistan. The basic principle behind nuclear stalemate is known as mutually assured destruction; in that, the need for self preservation outstrips the need to destroy the enemy. If two nuclear powers engage in an exchange, it is a zero sum game, both for them and probably for everyone else; nobody wins in a nuclear winter. However, if a side perceives that it is receiving a nuclear attack, it now has nothing to lose and could retaliate. Consider the possibility of an asteroid 80 ft. across striking the atmosphere. It enters the atmosphere at 50,000 M.P.H., which suddenly creates a barrier of compressed air in its path. The projectile is stopped dead by the friction created, converting kinetic energy a shock wave, in this case equivalent to the blast of a one-megaton bomb. The misinterpretation of this blast by a nuclear power could cause a nuclear exchange. (Shoemaker, 2001) Solutions: Apart from a global nuclear disarmament, providing poorer nuclear powers access to better data regarding Near Earth Object (NEO) activity should prevent any ‘misunderstandings’.

OZONE LAYER DEPLETION DUE TO HUMAN ACTIVITYIn this scenario, the threat is caused by the sun, but the problem caused by man. The ozone (O3) layer is the shield which prevents 97-99% of the ultraviolet light from the sun reaching usi. Ultraviolet light is categorized into UV-A, UV-B and UV-C. UV-C is utterly lethal to life, but is completely screened out by the ozone layer, the others also have harmful effects on organic matter, and progressive exposure to these forms can cause the formation of genetic mutations and cancers. Ozone depletion allows more of the UV radiation, particularly the more harmful wavelengths, to reach the surface. Much of the ozone depletion is caused by the release of Chlorofluorocarbons into the ozone layer. In CFCs, the disassociation of chlorine caused by UV light causes each chlorine atom to catalyse and remove tens of thousands of ozone molecules before decaying in the stratosphere. One CFC molecule can stay in the ozone for a century, destroying around 100,000 ozone molecules during that time (Columbia University , 2008). Therefore this is a problem that will continue to manifest itself, even if we no longer add to it.

Solutions: This problem is already being proactively addressed. The 1987 the Montreal Protocol, called for reducing CFC use by 50% by 2000. In 1992 an amendment of the treaty called for the end of CFC production in industrial countries by 1996. (United Nations Environment Programme, 2000). A way to address the residual problem that CFCs will cause in future would be to remove them from the atmosphere, plans are already being made to use powerful infrared lasers targeted at the troposphere, these beams would then selectively destroy CFC molecules through multiphoton dissociation. (Stix, 1993) Currently, the costs of such a project outweigh the potential merits, as the laser disassociation process is expensive and inefficient.

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Threats of Natural OriginNEAR EARTH ASTEROID (NEO) IMPACTSIt is believed that many extinction level events in the past were caused by impacts from large asteroids, evidence is found in large craters which remain, despite the earth’s geographically active surface. Objects 150m in diameter are dangerous enough to cause regional devastation for a land impact or the threat of a major tsunami for an ocean impact. Such impact events are predicted to occur once every 10,000 years or less. Larger objects possess the potential to do even greater damage, a rocky asteroid 200 miles across impacting land at 22 k/ms a second would cause a blast with a yield of 3.31 x 1012 megatons of TNT, an earthquake of 13 on the Richter scale, and displace a layer of ejecta 3310 m thick. (Marcus, 2005). This would probably doom all life, but the earth would not be significantly affected, apart from a large impact crater.Solutions: Although the level of possible devastation is linked to the size of the impacting object, thankfully larger objects are much easier to detect. In 1992 a US congressional mandate called for NASA to locate 90% of threatening near-Earth asteroids within the decade. A number of efforts which receive money through this mandate are all considered to be working on the informally titled Project Spaceguard, and many other countries have their own Spaceguard programs, including one in the UK, based in Powys. (Spaceguard UK Portal). There are currently 928 NEOs which are classified as potentially hazardous asteroids; however none of them come anywhere close to 200 miles in diameter. These asteroids do have an absolute magnitude of 17.75 or brighter, which roughly corresponds to at least 1 km in size, enough to potentially cause localized destruction in their impact zone, depending upon their composition and speed of impact. Being able to detect these objects is only the first phase of a solution. If an object was found to be on an impact course we would have to find a way to either change its direction or neutralize the threat it posed. Many solutions are being considered for both of these options, including interception with nuclear ICBMS. However, this creates the dangerous possibility of simply causing many smaller fragments to impact earth instead. Other proposed ideas include redirection via “pushing” with reflected solar energy, or by utilizing the solar wind by the attachment of kapton solar sails (Morrow, 2001)

Chixculub Crater Case Study (NEO)

It is now widely believed that the large-scale mass extinction of animal and plant species, known as the Cretaceous–Tertiary extinction event approximately 65.5 million years ago was caused by an asteroid impact in the region of the Yucatán Peninsula (Hildebrand, 1991). The Chicxulub Crater is greater than 180 kilometres in diameter, one of the largest impact created structures in the world. Evidence supporting this hypothesis comes from sedimentary rock layers found globally at the Cretaceous–Tertiary boundary. These contain a concentration of iridium hundreds of times greater than normal, and of a different isotopic composition of most terrestrial occurring iridium. Iridium is extremely rare in the earth's crust due to its great density; most of it sank into the earth's core while the earth was still molten. It is believed that the 10 kilometre impactor was a chondrite, a type of asteroid that contains large proportion of its mass as iridium. Correlating data from the estimates of the total amount of iridium in the K–T layer, and the size

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of the crater at Chicxulub; the asteroid is thought to have impacted with a force of 100 trillion tons of TNT. Other craters around the world have been dated to approximately the same age as Chicxulub, most significantly Silverpit crater in the UK and the Boltysh crater in Ukraine. This suggests that the asteroid that struck the earth could have been even larger, and fragmented upon contact with the atmosphere.

The effects upon life would have been substantial, apart from obliterating everything in the blast radiuses, the impacts would have displaced enough debris into the atmosphere to significantly diminish the sunlight received on the earth’s surface. These would have caused a lowering global temperature and inhibited photosynthesis, proliferating ecological food web disruptions and the extinction of over 50% of species present before the event, in a ‘nuclear winter’. (N Macleod, 1997). Global firestorms may have resulted from incendiary fragments from the blast returning to Earth. Analyses of ancient amber suggest that the oxygen content of the atmosphere was high (30–35%) during this period. A higher O2 level could have resulted in atmospheric combustion. If widespread fires occurred, they would have increased the CO2 content of the atmosphere and caused a temporary greenhouse effect once the dust had settled, exterminating the most vulnerable survivors of the "nuclear winter". Thankfully, disasters of this scale are expected to occur only once every 100,000,000 years.

GRAVITATIONAL DISTURBANCES CAUSED BY PROXIMITY TO MASSIVE CELESTIAL OBJECTSThe effects of this scenario vary in their extremity depending upon the mass of the object, the proximity, and angle of passage that the object takes. The concept is that, an object with enough mass could interfere with the gravitational equilibrium of the solar system. It is believed many of the comets which we are able to observe (possible threats in themselves) originated from a hypothetical region of space around 1 light-year away known as the Oort Cloud. The great distance of this cloud from the sun means that although the objects contained within it orbit the sun, they are more susceptible to the gravitational effects of temporarily passing objects. This disruption can redirect their courses and some of them are propelled towards the solar system, where their orbits can be trapped by the sun or the planets.

This gravitational process could be applied to Earth. An object that disrupted the orbit of earth significantly enough could cause enough of a change in distance to alter climate dramatically. An object with greater mass still could cause our planet to be ejected from the sun’s gravitational pull. Life could not survive the travel through interstellar space as it has evolved specifically in the sun’s warmth. It is known that Stellar-mass black holes travel through the Milky Way. Therefore there is a chance that one could pass by our solar system. One of these objects would have enough mass to cause all sorts of gravitational havoc, and because of its invisible nature (unless it had acquired an accretion disk), would be extremely hard for us to detect. However, significant gravitational interactions between the Sun and any object of stellar mass are expected to occur only once every 1019 years. It is believed extremely unlikely that we will endure the effects of a black hole before the Sun exterminates life on Earth. (J. Binney, 1987). Much larger mass black holes, former Quasars ejected from galactic mergers at speeds of around 10 million miles per hour (Than, 2007) are also believed to exist, and because of their speed, mass and angle of ejection, could orbit outside of the galactic plane, dipping in and out of the galaxy as their orbits take them. Gravitational interaction between one of these former Quasars and our solar system could be dramatic, enough to gravitationally capture our sun. Interaction between stellar mass objects also produces another apocalyptic possibility. Hypothetically, if a passing star where to collide directly with the sun, the merger would cause a

dramatic increase in the rate of fusion, if the colliding star had enough mass, the merger could create a supernova as the sun collapsed under this new gravitational instability (Sanders, 1970), this would definitely destroy the planet outright.Solutions?: Die? CHANGING SOLAR ENERGY OUTPUTAs far as we are aware today, this scenario is certain, but estimated to occur slowly, over billions of years. Our Sun is currently in the Main Sequence of its life, which means that it is fusing hydrogen to helium. Over the last 4.5billion years life has adapted to the conditions this creates on earth. However, once Sol depletes its supply of hydrogen, it will begin to fuse helium, and change in structure to a red giant star, brightening and increasing in size 100 times. Initially the increased solar output would increase temperatures upon the earth’s surface, disrupting the ecosystems and weather systems of the planet. Significant reduction of the amount of carbon dioxide, caused by a planet that is getting drier, would not allow for photosynthesis, and plants would die. This would cause a huge reduction in the amount of oxygen available; then animals would die. As the sun’s output increases, the oceans would begin to evaporate into the atmosphere, intensifying the greenhouse effect and absorbing more of the already significant solar output. By now, temperature change will have rendered the planet completely uninhabitable as conditions begin to mirror those found on Venus, which suffered the same fate due to its proximity to the Sun. As solar output rises, the very surface of the earth itself would begin to melt. Eventually, the earth would either be swallowed completely by the increasing size of the sun, or would increase its orbital distance as the sun’s gravitational pull weakens, due to the loss of solar mass.Solutions: In this situation there are two options, to either move the species to a more hospitable region, such as a mass migration to another planet. The more challenging solution to would be to directly alter the sun itself, this could be done by changing the predominant fusion process back to hydrogen, there would be no lack of fuel, as atomic hydrogen is the most abundant element in the universe. The challenge would stem from the star itself, how could we insert energy into a body that radiates energy so powerfully?

HOSTILE ETIHumanity has been broadcasting radio waves indiscriminately into space since the end of the 19th century. Many SETI (Search For Extraterrestrial Intelligence) organizations have also made efforts to communicate, by beaming concentrated microwave messages towards star systems that appear suitable. A number of SETI scientists criticize this, claiming it unwise to transmit to a species that we cannot know the motives of. Also, recent publications of US governmental documents suggest that the alien species are taken as a credible threat. (Andrews, 2008). If we are to assume that an alien civilization is capable of detecting our transmissions and travelling the incredible distance to reach earth in a timely fashion, we can assume their technology is vastly superior to ours. If this race for some reason chose to engage us in conflict, we could also reasonably assume that their superior technology would prevail, as the lessons of our own history have taught us. Solutions: This scenario allows for possibly the most unpopular solution humanity could ever devise, which would be to stop using technologies that transmit microwave and radio waves as a by-product of their use, this information blackout would silence our planet, but would not stop the continued passage of messages transmitted in years past, which will have travelled further than 90 light years. Despite the fact that alien life has not been found to exist, initial plans for planetary defence have been considered should the possibility of interstellar war emerge, based on a detailed analysis of modern warfare today and projected weapons developments over the coming decades. (Taylor, 2006)

GAMMA RAY BURSTSGRBs are created from the collapse of a massive star into a black hole, while inner portion of the star collapses to form the singularity; the outer layers erupt into space. Due to the Godlike power of this process, two beams of energy erupt from the polar regions of the dying star. Composed mostly of high-energy gamma rays, they can carry more energy in them than the Sun will put out in its entire lifetime. These are so energetic enough to be detectable across the universe, and have been proposed to have caused extinction level events in the past, most specifically the Ordovician-Silurian extinction event of 450 million years ago (Mellot, 2004). The effects of the earth receiving a GRB burst vary, depending on the distance from the emission, but simulations at the Goddard Space Centre suggest that a concentrated source of gamma rays would create nitrogen oxide compounds in the ozone layer, which would remove around 50% of its protective effects within a week. (Thomas, 2006 ) Apart from the excess UV exposure caused by a loss of ozone, the gamma ray dosage would be expected to be far in excess of a lethal for all life. These bursts are hypothesized to be able affect us even at distances five times the Milky Way’s width. (Golante, 2005)Solutions: Due to the nature of these bursts we could have no advance warning of their arrival. Theoretically the creation of some sort of planetary shield which would not interrupt the normal input of solar radiation would be required, but how it could be created is not known.

CONCLUSION

It seems that although many of these scenarios are highly improbable or hypothetical, the most dangerous natural threat comes from NEOs at this time. Much more pressing are threats of human causation, specifically the stockpiling of nuclear arms and the possible atrophy of the Ozone layer. Before watching the skies in terror we should look to our back yard.

Of course, the only way to really completely ensure the survival of mankind is to disperse it as far as possible across the universe, colonizing wherever we can. This would mean, barring an unforeseen event that brought an end to the physical universe, the species would endure in some way. Although this at the moment is just a far off idea, proactive steps can be taken to deal with the more probable threats which face us today.