Since my retirement in 1999 I have, in one way or another, dedicated my time and energy to asteroids, in one form or another. In particular near-Earth Asteroids, or NEAs. They’re actually part of a more general group, the NEOs or near-Earth Objects, which also includes near-Earth comets. Since we in the "biz" use the terms essentially interchangeably I'll use NEO. Just know that there are a few dead comets hanging out with those asteroids.
My initial interest in NEO’s was the role that they played, over geologic time, in defining the Earth’s environment and in shaping the evolution and development of life. The history of asteroidal and cometary impacts on the Earth, and indeed all solar system bodies, is most evident when looking at the pockmarked surface of the moon. However, it is generally understood that the cratering evident there is no different from what it would be on other inner solar system bodies, but for the mitigating effects of atmospheres, weather and other forms of erosion.
Using the diameter of a lunar crater one can determine the energy and approximate size of the impactor (asteroid or comet) that caused it. One can then assume that the number of such impactors hitting the Earth over the same period of time was greater by a factor of 10, given the Earth’s larger cross section and higher gravity.
Based on an analysis of lunar crater ages, it appears that the flux of the NEOs has been approximately constant for the last 3.5 billion years, i.e., once the first billion years of the solar system’s childhood were past. With these observations one can approximate the current frequency of impacts of varying sizes. E.g., we can expect 1 impact every 100 million years by an object 10-15 km. in diameter. And, indeed, it appears that the dinosaurs, and 75 % of species living on Earth with them were destroyed 65 million years ago by such an impact near the Yucatan Peninsula, the so-called Chicxulub impact.
Other historic mass extinctions (major die-offs of life in the geologic record) may also have been caused by NEO impacts and there is some evidence to support this. What is abundantly clear in studying these episodic but devastating events is that the developing tree of life on Earth was “pruned” time and time again by this cosmic gardener.
So my specific interest in NEOs is the possibility of terminating this cosmic gardener’s activities, now that we have come to know of his habits. And, given our cleverness in the development of technology, we are just about at the point where we can actually pull off this cosmic feat.
BTW, an alternative way to think about this "cosmic feat" is that, by diverting asteroids otherwise headed our way, we're slightly modifying the clockwork of the solar system to enhance the survival of life on Earth. Equally important (and surprising) is that the cost of doing this is virtually negligible. (Less than 1% of the current NASA budget would be ample)
The two keys to enabling this amazing capability are 1) to detect, catalog and track all potentially damaging NEO (those over ~40 meters in diameter), and 2) develop and deploy a system to rendezvous with any NEO coming our way and nudge it such that it will miss the Earth vs. hitting it.
The first detection program levied on NASA by the US Congress was completed around 2010, the Spaceguard Survey having discovered over 90% of the NEOs larger than 1km in diameter. To date we have discovered and are tracking ~97% of all these large NEOs. In 2005 Congress upped the game and directed NASA to discover over 90% of the NEOs 140 meters diameter and larger by 2020. Unfortunately this goal will not be met. With the current and anticipated telescopes the actual discovery statistics for these intermediate sized NEOs will probably be in the 50% range. NEOs in this size range would create regional (think statewide) devastation.
What we know today is that NEOs down to about 40 meters in diameter, were they to impact directly above any city on Earth would devastate that city. If the ultimate goal of a planetary defense program were to fully protect life from all asteroid impacts our capability for detection and tracking would need to be significantly enhanced beyond any discovery programs currently being considered. Nevertheless the capability to discover and integrate this population into the planetary defense database is being explored and may well be possible within a decade or two.
The existing discovery and tracking program is very well described and fully open to the public. NASA's Center for Near Earth Object Studies (CNEOS) website is updated by telescopic observations daily, and while technical, is quite accessible. In particular an automatically updated set of summary tables and a table of perceived risks (the Sentry program) are very informative. Many additional links on the latter page lead to a vast amount of background on this issue.
The issue of mitigation, however, has barely been touched. And it is here that I and a number of others have attempted to organize productive activity. NASA has now organized a Planetary Defense Coordination Office and has received increased funding for research and testing of deflection concepts. The first mission to actually alter the orbit of an asteroid (the Dart mission) is now planned for launch in late 2020. If fully funded and successful the first deflection (of a non-threatening) asteroid will have been accomplished by the end of 2022.
What is clear is that impacts from NEOs occur as the ultimate event of millions of years of dancing between the Earth and the NEO population. There are approximately 1000 NEOs over 1 km. in diameter that orbit the Sun in trajectories that cross the Earth’s orbit. These orbit tracks shift around over long periods of time due to a number of gravitational perturbations and from time to time intersect the orbit of the Earth. On rare, but statistically predictable occasions, the Earth and the NEO will meet at that point of intersection of the orbits. In the general case, however, such an impact will occur only after millions of orbits where the NEO and the Earth pass by each other in the clear. The Sentry program, and others like it, project ahead and allow us to determine up to 100 years or more into the future whether or not any given NEO will pay us a visit.
Therefore, in the case where we have already detected the asteroid, we will know of any upcoming impact decades ahead of the event. Given this advanced warning it will be possible to launch a space campaign, most likely comprised of a reconnaissance and observing spacecraft preceding an impacting spacecraft. The kinetic impactor would crash into the NEO slightly altering its velocity such that several years later it will pass just in front of or just behind the Earth rather than hit it. Changing the NEO's speed by as little as 0.02 mph is generally enough to cause the asteroid to miss Earth vs. pay us a direct visit.
The rub, of course, is that our current database is complete only for the big, civilization destroyers, the NEOs 1 km. in diameter and larger which hit us, on average, every several million years. We now know of and track about 97% of these large objects. It is, however, the million or so smaller asteroids between 40 meters and 1 km. that hit much more frequently and can each kill millions of people which we must focus on. By way of example, even a 100 meter diameter NEO packs a wallop equal to 100 megatons of TNT. This is about double the size of the largest nuclear weapon ever created by humankind and, because of our lack of knowledge we could be hit by such an object by complete surprise. The "Tunguska Event" in 1908 was caused by a small 50-60 meter stony asteroid that exploded in the lower atmosphere over a remote location in Siberia with a force of about 15 megatons. It completely flattened and ignited over 800 square miles of forest. Had it hit over a major city instead of the wilds of Siberia, millions of people would have been killed.
Even the 18 meter diameter Chelyabinsk asteroid that streaked through the early morning sky just south of that city on February 15, 2013 came very close to having killed someone. That impact sent over 1500 people to the hospital with mostly minor cuts from flying glass, and over 7000 buildings were damaged. The explosion, high in the atmosphere, released an amount of energy over 30 times that released by the Hiroshima atomic bomb. These impacts are powerful!
So if we are to act responsibly we must first detect and track these smaller NEOs in order to provide ourselves adequate warning time. Then, after detecting an unwanted visitor we would launch a space campaign to deflect it harmlessly to the side. Since we have no chance to protect ourselves against what we don't know, informed elements of the scientific community are urging the government to accelerate the current detection rate by a factor of 100 and to complete the inventory down to NEOs of about 40 meters in diameter. Additionally, increased attention needs to be directed at fully understanding and testing our deflection capability.
Virtually all of the issues mentioned above relate to the technological work of finding, tracking, predicting, and preventing future impacts. What is surprising, even shocking, is the realization that the most challenging, and ultimately uncertain component of preventing future asteroid impacts is not a technological challenge, but a geopolitical one! To understand this one needs to picture a point on the Earth at which a NEO headed for an impact will hit. Then picture that a deflection mission is executed but that it nudges the asteroid much to gently. This would change the impact point but the asteroid would still impact. A bit harder nudge would have shifted the impact point a bit further. Connected, these three points will lie along a line, and if you extend this line all the way across the Earth and off into space you have what we refer to as the risk corridor. If you speed up or slow down the asteroid enough you will shift the asteroid's impact off the back end of the Earth, or off the leading edge of the Earth, respectively (Yes, this is correct, and counterintuitive!). This is a successful deflection. However, if something goes wrong and the deflection changes the NEO's velocity too little it is going to hit elsewhere in the risk corridor, closer to the leading or trailing edge of the Earth... but hit the Earth it will.
So in every deflection, no matter what technique one uses, people (and nations) who were not originally at risk will be placed at increased risk (the possibility of a partial deflection) in order to eliminate the risk to everyone. The people/nations put at elevated risk by a deflection are those who lie along the risk corridor between the original impact point and the edge of the Earth targeted by the deflection. Now to "get" the geopolitical conundrum just think of people who lie along the risk corridor, and their political leaders, who, if they lie between the original impact point and the leading edge of the Earth, if the deflection is planned in their direction. They will all (likely) say, "deflect it the other way!". And, of course, those on the opposite end of the risk corridor will say the converse. So who decides? Which way to deflect it? East or west? West or east? Or, why deflect it at all? These decisions, and dozens more like them, are not technical in nature. They are political. And they must be made 5-10 or more years ahead of the potential impact. This is serious and extremely controversial geopolitical decision making! And this is precisely why the ASE NEO Committee took this issue into the United Nations. Like it or not, the UN is about the only institution that represents everyone on the planet. So make no mistake, this will be a planetary decision.
Hence the purpose of the B612 Project, for the ASE's work in the UN's Committee on the Peaceful Uses of Outer Space, and in Asteroid Day's focus on public education about asteroids, is to prepare to save the lives of potentially thousands or even millions of people on that day, certain to come, when we discover that a substantial asteroid is heading for an impact.
Good luck, right? Feel free to join in. Nothing like being part of the largest environmental project of all time!
You should know that since B612 Foundation, the ASE and the Asteroid Day Foundation are all non-profit 501(c)3 organizations any contributions you make will be tax exempt. The websites below will allow you to make direct contributions to support their work, and all contributions will be appreciated.
Thank you.
