How Observation Increases the Risk of Rare Catastrophic Events

The Case of NASA's Asteroid Program

By
Asteroid Belt Around Sun Sized Star
How Observation Increases the Risk of Rare Catastrophic Events : The Case of NASA's Asteroid Program - Edward Moe

Abstract

A consideration of NASA's asteroid observation mission highlights the possibility that for rare events observation is not unambiguously positive. Although measurement is beneficial in the long run, and is required for eventual risk management or mitigation, it may at first actually increase the expected value of the risk. In the case of the asteroid mission, observation created a substantial risk of false positives that greatly outweighed the initial potential risk reduction from early warning or asteroid diversion, such that the total risk increased. These dynamics are explored with a simple model that can be extrapolated to improve the risk calculation for any rare threat.

Introduction

Asteroids have the demonstrated capacity to destroy entire cities or even to cause the worldwide extinction of humanity. When considering the question of risk mitigation for such a monumental threat, it seems self-evident that more information would always be beneficial. After all, observation of asteroid prevalence allows calculation of the risk level and determination of the appropriate costs to address it. However, NASA's asteroid observation mission suggests that it is not always this straightforward. In fact, measurement of very rare events may initially increase the threat and lead to increased spending on mitigation.

Beginning in the late 1990s, NASA began to compile a catalog of asteroids, comets, and other Near Earth Objects (NEOs) orbiting close to the Sun. Since then, scientists have cataloged over 95% of all NEOs with diameters larger than 1 km (hereinafter d >1 km) that would cause global devastation if they hit the Earth, as well as thousands of smaller asteroids with the power to flatten cities or destroy regions. As their work continued into the decade — and the known NEO list grew — the overall level of fear of an asteroid impact rose rapidly among politicians and journalists. In 2005, NASA's mandate was extended and in 2011, after 12 years of operating on a relative pittance, the NEO Program’s budget for asteroid observation and diversion studies increased fivefold.

Note, however, that this is not a simple case where more data increased the estimate of the expected value of the threat, rationally justifying greater attention.[1] Actually, during the decade leading up to 2011, the expected value of impact had probably decreased. Rather, the very fact of observation had created new risks and opportunities that changed the calculation of the total threat level. Specifically, observation created a substantial risk of reacting to false positives that initially outweighed the opportunity for risk reduction via early warning or asteroid diversion.

This paper lays out these dynamics with a simple model for risk management of rare events. It begins with an overview of the changing response to the asteroid threat, and demonstrates that there was a significant increase in attention towards this risk. Next it shows that this cannot be explained rationally by an adjustment in the expected value of impact. Rather, the immediate threat of responding to false positives actually increased the estimate of total risk. This model shows how observation, though beneficial in the long term, can increase short-term risk and force additional spending on mitigation.

Observing the threat: The NEO program

In 1994, NASA began to evaluate a Congressional proposal to catalog potentially hazardous asteroids, and formed the NEO Program to improve the measurement of this threat in 1998. It was originally given a $4 million budget, and tasked with recording 90% of all d >1 km NEOs by the end of the decade, a mission it completed in 2010.[2] This mission to evaluate the likelihood of an extinction-level asteroid impact was an unqualified success and in 2005, Congress expanded NASA’s responsibilities to include a catalog of 90% of d >140 m NEOs by 2020. By 2011, NASA had cataloged over 7000 midsized NEOs, and was able to reduce its prediction of total NEO quantity substantially. However, it was clear early on that without an expanded budget, the 90% goal was never going to be met.[3]

This observation program had a noted effect: Although the vast majority of meteors go unnoticed because they either burn up in the atmosphere or impact in the ocean, with more resources directed to the search more were spotted and more made it onto the front pages of the news. For example, in 2004, the massive asteroid Apophis (d = 325 m) was initially assigned a 2.7% chance of hitting the Earth, and continued to appear very threatening until 2006.[4] Similarly, in 2008, the tiny asteroid 2008 TC3 (d = 2-5 m) became the first meteorite ever to be observed before entering the atmosphere.[5] As more potentially hazardous asteroids were seen, the threat garnered increasingly significant media attention.[6]

The rising level of worry was more than just a fleeting response to newsworthy asteroids. Congressional hearings, impact event wargames, and international risk mitigation conferences were held, all warning that Earth was grossly unprepared for the asteroid threat. The most concrete evidence of this worry was the 2011 increase in the NEO program’s budget. For the first time in 12 years, it increased funding five-fold to $20.4 million. In addition to accelerated NEO cataloging, the budget included new support for research into asteroid diversion and risk mitigation techniques. In contrast, the overall spending on non-defense research actually decreased slightly from 2002 through 2014, as did NASA’s total budget.[7] In fact, using constant dollars, NASA's budget was lower during 2011-2014 then at any time since 1988, and in 2011, the agency actually received 13% less than in 2010. Given that the NEOs program's budget increased at a time when most others were shrinking, it's fair to say the asteroid threat was considered a priority, and that it was now seen as significantly more important.

Explaining interest in NEOs: The theory

In the traditional economic view of risk pioneered by Frank Knight, observation of an unfamiliar threat leads to measurement and the ability to sell insurance at a price appropriate for the expected value of the risk.[8] Any such movement from uncertainty to calculated risk is thus inherently beneficial to society. Unfortunately, this view is insufficient to explain the current case. Though it seems intuitive that more data about the likelihood of an asteroid impact led to a rational increase in funding, this is not borne out by the evidence. Rather, the situation can best be explained by an emotion-amplified response to an increasing perceived threat level, which was a consequence of the increasing real threat level created by the very fact of observation.

First, it’s necessary to address the psychological and emotional element of the story. Essentially, the dynamics of the asteroid threat were exactly those most likely to lead to an overblown emotional response in line with all of the cognitive biases predicted by behavioral economics. A hitherto incomprehensible threat had become understandable and seemed to be growing, just as technology promised to solve it. Early false positives made the asteroid threat cognitively available, the vanishingly small risk from meteorite impact was overvalued, and in the face of certain loss, decision-makers sought out the gamble of maybe getting lucky with an asteroid diversion strategy straight out of science fiction. In behavioral economics, this is a “risk-seeking choice.”[9] This emotional response may well be sufficient to explain the observed budget increase, but such an explanation neglects important dynamics in the total risk calculation. Instead, this idea of perceived threat can be most useful in the background, underlining the importance of actual changes in threat level.

The apparent contradiction of the total risk story is far more compelling. A decade of observation had dramatically reduced the uncertainty surrounding NEOs, and the predicted probability of an impact event had, if anything, lowered by 2011. At the same time however, measurement fundamentally changed the expected value calculation by creating new artificial risks and offering the possibility of reducing existing ones. Critically, because the newly-created risks were immediate while the benefits were at first only theoretical, the total risk level actually grew.

The following identity may be helpful for this explanation:

Total Risk = EV(Impact – Reduction) + EV(False Positive)

Since the probability of an asteroid hitting the Earth is constant and practical measures to prevent potential future impacts are slow to develop, the expected value of an impact should be fairly constant at first. However, observation immediately generates the risk of false positives, thereby increasing the total risk. In the long run, early warning and the use of threat mitigation technologies are expected to reduce both impact and false positive risks, generating the total risk reduction projected in Figure 1. The remainder of this paper will map the evidence onto the model to show how these predictable dynamics related to the increase in the importance assigned to the NEO threat.

Figure 1: Model Predictions

A constant expected value of asteroid impact

Analysis of the contemporary view of the risk of impact shows that the 2011 budget did not increase because of a rise in the estimation of the expected value of an asteroid impact. Nor is it plausible that it represented nothing more than a spontaneous recognition of a commonly known threat. In fact, additional observation provided increasing confirmation of a predicted power law distribution that hadn't been changed much since the early 90s. If anything, the expected value of an asteroid impact decreased somewhat after 1994, even before taking into account any of the practical potential benefits of observation. Thus, the alternate hypothesis of a rational recalculation can be rejected.

This is not to say that the threat is insignificant. Although most meteors burn up in atmosphere, larger meteorites can be a real threat. The classic examples are the Chicxulub asteroid (d >10 km), thought to have caused a global extinction 66 million years ago, or the 1908 Tunguska asteroid (d = 120 m) that impacted with an estimated force equivalent to 15 MT of TNT and flattened 800 mi² of Siberian forest.[10] In 2013, the much smaller meteor (d = 19 m) that exploded over Chelyabinsk, Russia still had a force of around 590 kT, and caused more than a thousand injuries.[11] The difference in destructive potential increases as a function of diameter, and d = 100-140 m is approximately the boundary between local and regional destruction.

Fortunately, asteroids appear to follow a power law distribution, such that larger asteroids are far less common than smaller ones (see Figure 2). Reviews of the NEO population, for example by Brown et al. in 2002, Bland and Artemieva in 2006, and Moon et al. in 2007 re-established impact frequency estimates in line with research from as early as 1991.[12] Moreover, new data gathered by the NEOWISE satellite showed that the total number of d >100 m asteroids was about 40% lower than previously believed, that over 90% of the d >1 km asteroids had indeed been discovered, and that all of the d >10 km asteroids were likely known. By 2011, the large asteroid catalog provided substantial evidence that the likelihood of a massive impact in the following 100 years could be discounted.[13]

Figure 2: Frequency and Consequences of Impact[14]

Although expected value calculations built on this power law have long shown that asteroid mitigation has been chronically underfunded, estimates did not change much during the decade.[15] A 150 m asteroid could be expected to cause $59 million damage on average, and a catastrophic 73,000 deaths, although if it hit a more densely populated region, the number could easily be in the millions of deaths and trillions of dollars. Averaging for frequency, expected value for impacts of 60-1500 m asteroids is perhaps 50–3000 deaths per year.[16] Similarly, Chichilnisky and Eisenburger calculated the expected value of an extinction level event at $4-500 million per year, but concluded reasonably that the rational actor “should spend as much money today on defenses against extinction as can be usefully transferred into improved protection.”[17]

This calculation shows that in 2011 (as in every previous year), increasing the budget was likely a rational option. However, given the sufficiency of alternate explanations, it seems implausible that the core change was simply decision-makers’ recognition of the expected value of an impact event. After all, over the period, expected value of an impact had stayed relatively constant or possibly even decreased slightly. Therefore, it is much more likely that artificial risks and the new possibility of deflection explain the corresponding increase in the budget.

Reducing EV of Impact: Early warning and diversion

With improvements in the observation program, by 2011 it was becoming increasingly likely that there might be some warning before impact. Particularly in the case of large asteroids, it was probable that substantial forewarning would give time to attempt a diversion mission. Both of these possibilities represented real risk mitigation made possible by observation. Beyond the expected value implication, there is certainly also psychological value to this implied sense of agency.

The observation program is highly automated and efficient, and the record of known asteroids has been growing rapidly. Cataloged asteroids’ orbits are logged, and their likelihood of hitting the Earth is calculated. NEOs with d >100 m that have a non-trivial impact probability are categorized as potentially hazardous objects (PHOs), and are flagged for follow-up. With each additional observation, the probability of impact is refined. The fraction of PHOs is decreasing, and given the observation mission’s advanced telescopes, it's just a matter of time before the d >140 m catalog is as complete as the d >1 km list.[18]

As the catalog grows and our capability to detect smaller and smaller asteroids increases, warning before an impact event might give time to evacuate cities and/or to move people to shelters. With Chelyabinsk, the majority of the injuries were due to broken glass from the pressure wave, and this category of injury could easily have been prevented even with a few minutes warning. Similarly, as in the case of earthquakes, even a few seconds notice could be sufficient to protect fragile power systems, reduce the speed of trains, and alert emergency responders.[19] Functionally, NASA remains far from being able to reliably predict smaller asteroids, but even by 2011, the capacity to detect a meteorite before impact was greater than ever before.

As for asteroids large enough to cause a global extinction, it is now a practical certainty that they would be detected long before impact. Thus, in the future, major asteroid impacts could be prevented by diversion or destruction in space. Moreover, as the technology matures, it is likely that the range of targets will expand such that diversion becomes possible for large and small potential meteorites alike. Whether or not consistent asteroid diversion becomes possible soon, the idea remains enticing. While the emotional significance of an extinction level impact some time in the next million years is easy to discount, diversion preparation will quickly seem very useful indeed when a significant threat is discovered in the PHO catalog.

Much theoretical and practical research has gone into developing strategies to divert or even destroy such a threat before impact. Options include standoff or subsurface nuclear strikes, kinetic impactors that would nudge distant PHOs off-target, and solar concentrator apparatuses that could slowly push distant asteroids out of the path of the Earth over the course of a decade or more.[20] Still, most of this work is theoretical and mitigation presents practical challenges. Current best-case scenarios suggest that any response other than a nuclear strike on a small asteroid would take a decade or more of preparation (see figure 3).[21] 2011’s expanded budget included funding for such research, explicitly showing that lawmakers considered the value of reducing the threat of impact.

 

Figure 3: Diversion Strategy by Warning Time[22]

Compared to the expected damage from a mid-sized asteroid, the estimated costs for a diversion mission are small. Gritzner and colleagues estimate that an emergency diversion mission would start at about $500 million.[23] Matheny estimates that a $20 billion diversion system could buy 100 years of security and would be cheap at a cost of $2.5/life-year saved.[24] Another strategy that NASA has pursued has been to develop capabilities through multipurpose tasks. This explains projects such as the asteroid capture mission that seeks to evaluate the plausibility of bringing an asteroid into a nearby orbit for mining, or the European Space Agency’s Deep Impact mission that both tested the core of a comet and evaluated the idea of redirecting it with a kinetic hit.[25] With further research, mitigation will only become more cost effective.

In summation, at a time of high concern over impact events, the real risk had actually never been lower. Even without a funding increase, the expectation would have been for the real risk to continue to fall because of early warning. It’s therefore useful to look to newly created opportunities to help explain the rise in attention. Both in the case of expanding early warning and building up deflection capabilities, we see that a new incentive had developed. Before, when future asteroid strikes were unpredictable and unpreventable, there was little motivation to invest. Now that there is potential to effectively mitigate a threat, the option looks much more appealing.

The heightened risk from observation

Unfortunately, at the same time that the NEO Program was hinting at risk reduction opportunities for the future, observation was creating hazards in the present. First, the increase in PHO recognition immediately created the real possibility that a false positive or an overvalued low impact probability could lead to an expensive and unnecessary mission. Second, there was the chance that any mission might do more harm than good. These risks can be expected to eventually decrease as observation becomes more complete and mitigation more effective, but certainly as of 2011 they were only growing. Reducing these artificial risks provides a very strong incentive to accelerate asteroid cataloging.

While the vast majority of PHOs in the NASA database have extremely low calculated probabilities of impact, given a lack of the follow-up tracking needed to confirm PHO trajectories, the total number is consistently growing.[26] In 2010, NEO program executive Lindlay Johnson informed NASA’s Planetary Defense Task Force that around 20% of all known asteroids were cataloged as threats.[27] With an average of 77 NEOs discovered each month in 2010-2011, there was a real and substantial threat of a large PHO being assigned a predicted impact date mere decades in the future and forcing a reaction.

This problem comes from the simple fact that observation is extraordinarily difficult. Asteroids may be impossible to see for decades at a time, be observed again only by pure luck, or have shapes/spins/trajectories that make them nearly impossible to predict. In the case of the Apophis asteroid for example, if it passed through a miniscule patch of space (“a keyhole”), it would be nudged by the Earth's gravity in such a way as to make a future impact practically certain. However, it was not immediately clear whether it would be possible to tell if Apophis would hit the keyhole before it happened, years in the future.[28] Although its threat was discounted two years later, Apophis was briefly the most dangerous asteroid ever observed.[29]

In a 2010 letter to Nature, Eugenie Reich described the threat clearly: “Some time in the next decade, a US president will probably be presented with this dilemma: Is it worth spending US$1 billion to deflect a space rock that may never hit Earth?”[30] She also referenced Johnson's fear that regardless of the actual probability of impact, politics might demand a response. Given the long preparation time required for a successful mission, substantial investment may be required before the threat can even be confirmed. Given the exceptional unlikeliness of a significant impact, the expected value of paying to prevent a false positive could potentially be even larger than the total expected value of impact in a given year or decade.

Perhaps more counterintuitive is the possibility that perceived mitigation capabilities could actually present an additional risk. The theoretical possibility of a successful diversion may force an attempt to deflect a potential meteor whether or not appropriate technology can be made ready in time. Only nuclear technology has seen any practical testing, and developing an entirely new weapon system with a short, urgent deadline is a recipe for disaster. One mistaken calculation, minor malfunction, or instance of plain bad luck could turn a nuclear strike into a cure worse than the disease. A recent model of small meteorite damage suggests that fragmentation of a mid-sized asteroid would actually amplify the destruction, as well as spreading out the harm.[31]

A related risk is the often-mentioned moral and political issue that during the course of a diversion, the predicted impact zone will cross over areas previously considered safe as the approaching asteroid’s path is altered. Likewise, if a single meteorite is fragmented into many, it could threaten new populations. This is made all the more worrying by the fact that any mission would likely be funded and led by the United States, whether or not it was most at risk. The chances for misaligned incentives are nontrivial, as threats to Americans might be weighted more heavily, leading to a US-centric defense.

Regardless of the amount of investment in risk mitigation justified by the expected value of impact, it seems likely that more should be spent to alleviate these artificial risks. In addition to the economic costs, strongly reacting to a false positive could delegitimize attempts at risk mitigation, setting the program back years or decades, and potentially reducing trust in future predictions. Although a causal link cannot be shown, these artificial risks from the very fact of observation provided justification for increased spending.

Conclusions

The negative consequences of observation cropped up far sooner than the possible benefits, but there is reason to believe that they will diminish as observation continues. In fact, better tracking will simultaneously reduce the risk of false positives and improve early warning of impact. At the same time, further research into mitigation may eventually reduce the threat of catastrophic impact. If attention and resources remain directed against this threat, it may one day be possible to detect and deflect both major and minor asteroids. Simultaneous reductions in impact and false-positive risks will reduce the long run total risk level.

The fundamental conclusion from this case is the cautionary message that observation of extremely rare or uncertain events can both make them seem more likely and create new artificial threats. This verdict must be taken into consideration whenever risk levels are estimated or mitigation is attempted. Even if the long run goal of measurement promises a significant benefit, it may be advisable to hold off on initial observations until substantial resources can be directed to the problem, in order to quickly speed through the period of increased risk. On the other hand, for an activist seeking to draw attention to a rare hazard, beginning to gather data could potentially raise the real and perceived risk enough to force a meaningful response.

In the particular case of the asteroid threat, additional spending on risk mitigation certainly seems appropriate. As an absolute minimum, mitigation of the artificial risk should be prioritized. At the same time, international cooperation on this issue is necessary both to increase research into risk mitigation and to establish mechanisms to dictate an appropriate response to potentially threatening asteroids in the future.

Notes & References

  1. Throughout this paper, risk is described precisely: total risk is the expected value (EV: probability-weighted average of all possible values) of the asteroid threat in economic terms. It is the sum of real risk (EV of damage from meteorite impacts) and artificial risk (EV of costs of responding to false positives).
  2. Mainzer, A., T. Grav, J. Bauer, J. Masiero, R. S. McMillan, R. M. Cutri, R. Walker, et al. “NEOWISE Observations of Near-Earth Objects: Preliminary Results.” The Astrophysical Journal 743, no. 2 (December 20, 2011): 156.
  3. Lindlay Johnson, “Near Earth Object Observations Program,” Presentation to Planetary Defense Task Force (April 15, 2010).
  4. “Herschel Intercepts Asteroid Apophis,” European Space Agency, accessed November 4, 2014, http://www.esa.int/Our_Activities/Space_Science/Herschel_intercepts_asteroid_Apophis.
  5. Chesley, Steve, Paul Chodas, and Don Yeomans. “Asteroid 2008 TC3 Strikes Earth: Predictions and Observations Agree.” NASA, November 4 2008. [Accessed 03/03/2015]. http://neo.jpl.nasa.gov/news/2008tc3.html.
  6. Remo, J. L., and H. J. Haubold. “Threats from Space: 20 Years of Progress.” Bulletin of the Atomic Scientists 70, no. 4 (July 1, 2014): 85–93.
  7. AAAS, “Trends in Federal R&D, FY 1976-2015.” http://www.aaas.org/sites/default/files/DefNon_0.jpg.
  8. Knight, Frank H. Risk, Uncertainty, and Profit. 1921. Library of Economics and Liberty. Retrieved March 29, 2015 from the World Wide Web: http://www.econlib.org/library/Knight/knRUP.html
  9. Note the uncanny similarity to the conditions that trigger non-rational decision-making. For example, Amos Tversky and Daniel Kahneman, “Advances in Prospect Theory: Cumulative Representation of Uncertainty,” Journal of Risk and Uncertainty 5, no. 4 (October 1, 1992): 297–323, doi:10.1007/BF00122574; Timur Kuran and Cass R. Sunstein, Availability Cascades and Risk Regulation, SSRN Scholarly Paper (Rochester, NY: Social Science Research Network, October 30, 1998), http://papers.ssrn.com/abstract=138144.
  10. Phillips, Tony, “The Tunguska Impact—100 Years Later,” (June 30, 2008). http://science.nasa.gov/science-news/science-at-nasa/2008/30jun_tunguska/
  11. Popova, Olga P., Peter Jenniskens, Vacheslav Emel’yanenko, Anna Kartashova, Eugeny Biryukov, Sergey Khaibrakhmanov, Valery Shuvalov, et al. “Chelyabinsk Airburst, Damage Assessment, Meteorite Recovery, and Characterization.” Science 342, no. 6162 (November 29, 2013): 1069–73.
  12. Bland, Philip A., and Natalya A. Artemieva. “The Rate of Small Impacts on Earth.” Meteoritics & Planetary Science 41, no. 4 (April 1, 2006): 607–31.
  13. Clavin, Whitney and Dwayne Brown. “NASA Space Telescope Finds Fewer Asteroids Near Earth.” NASA, September 29, 2011. [Accessed 03/02/2015]. http://www.nasa.gov/mission_pages/WISE/news/wise20110929.html.
  14. Johnson, op. cit.
  15. Viscusi, W. Kip, “The value of risks to life and health,” Journal of Economic Literature 31, no. 4 (December 1993):1912-1946.
  16. Gritzner, C., and S. Fasoulas. “Justification of NEO Impact Mitigation Activities by Risk Management.” Memorie Della Societa Astronomica Italiana 73 (September 1, 2002): 747.; Gerrard, M. B. “Risks of Hazardous Waste Sites versus Asteroid and Comet Impacts: Accounting for the Discrepancies in U.S. Resource Allocation.” Risk Analysis: An Official Publication of the Society for Risk Analysis 20, no. 6 (December 2000): 895–904.; Gritzner, Christian, Kai Dürfeld, Jan Kasper, and Stefanos Fasoulas. “The Asteroid and Comet Impact Hazard: Risk Assessment and Mitigation Options.” Die Naturwissenschaften 93, no. 8 (August 2006): 361–73.
  17. Chichilnisky, Graciela, and Peter Eisenberger. “Asteroids: Assessing Catastrophic Risks.” Journal of Probability and Statistics 2010 (August 1, 2010).
  18. http://neo.jpl.nasa.gov/risk/doc/sentry.html
  19. http://Earthquake.usgs.gov/research/earlywarning/
  20. Bruck Syal, Megan, David S. P. Dearborn, and Peter H. Schultz. “Limits on the Use of Nuclear Explosives for Asteroid Deflection.” Acta Astronautica, NEO Planetary Defense: From Threat to Action - Selected Papers from the 2011 IAA Planetary Defense Conference, 90, no. 1 (September 2013): 103–11.
  21. Sanchez, Pau, Camilla Colombo, Massimiliano Vasile, and Gianmarco Radice. “Multicriteria Comparison Among Several Mitigation Strategies for Dangerous Near-Earth Objects.” Journal of Guidance, Control, and Dynamics 32, no. 1 (2009): 121–42.; Gritzner et al., op. cit., “The Asteroid and Comet Impact Hazard”; A. C. Charania, “Planetarydefense.blogspot.com: JPL/B612 Paper on Apophis Keyholes,” accessed November 1, 2014, http://planetarydefense.blogspot.it/2009/08/jplb612-paper-on-apophis-keyholes.html.
  22. Peter, Nicolas, Andrew Barton, Douglas Robinson, and Jean Marc Salotti. “Charting Response Options for Threatening near-Earth Objects.” Acta Astronautica, New Opportunities for Space. Selected Proceedings of the 54th International Astronautical Federation Congress, 55, no. 3–9 (August 2004): 325–34.
  23. Gritzner et al., op. cit., “The Asteroid and Comet Impact Hazard.”
  24. Matheny, Jason G. “Reducing the Risk of Human Extinction.” Risk Analysis: An Official Publication of the Society for Risk Analysis 27, no. 5 (October 2007): 1335–44.
  25. Fox, Steve. “Asteroid Initiative.” NASA, June 20, 2013. http://www.nasa.gov/mission_pages/asteroids/initiative/index.html.; Perez, Martin. “Mission to a Comet,” Text, NASA, (July 18, 2013), http://www.nasa.gov/mission_pages/deepimpact/mission/index.html.
  26. Reich, Eugenie Samuel. “NASA Panel Weighs Asteroid Danger.” Nature News 467, no. 7312 (September 8, 2010): 140–41.
  27. Johnson, op. cit.
  28. http://neo.jpl.nasa.gov/apophis/
  29. “Herschel Intercepts Asteroid Apophis.” European Space Agency. [Accessed 11/04/2014]. http://www.esa.int/Our_Activities/Space_Science/Herschel_intercepts_asteroid_Apophis.
  30. Reich, op. cit.
  31. Shuvalov, V. V., V. V. Svettsov, and I. A. Trubetskaya. “An Estimate for the Size of the Area of Damage on the Earth’s Surface after Impacts of 10–300-M Asteroids.” Solar System Research 47, no. 4 (July 1, 2013): 260–67.
Edward is an MA candidate at Johns Hopkins SAIS, focusing on European Studies and Quantitative Economics. His earlier research has looked into the social psychology of social movement behavior and the consequences of nationalism and EU Accession for minority rights movements in Serbia. He is currently engaged in an investigation of UN voting patterns, learning about the process of past and prospective convergence.