My current primary interest is the subject of Near Earth Asteroids, or NEAs. They’re actually part of a more general group, the NEOs or Near Earth Objects, which also includes comets.
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 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 just about 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 increasing 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.
The two keys to enabling this amazing capability are 1) to detect, catalog and track all potentially damaging NEAs (those over ~100 meters in diameter), and 2) develop and deploy a system to rendezvous with any NEA coming our way and nudge it such that it will miss the Earth vs. hitting it.
The detection program is well underway, for the largest of the NEAs of concern, i.e., those over approximately 1 km. in diameter. A follow-on program to detect and track those NEAs between 0.1 and 1.0 km. diameter has recently been recommended by a NASA study but no action has been taken on it to date. The results of the current detection program are reflected on the web at the primary NASA site at JPL. 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 hardly been touched. And it is here that I and a number of others are attempting to organize productive activity. What is clear is that impacts from NEAs occur as the ultimate event of millions of years of dancing between the Earth and the NEA population. There are likely between 1000 and 1200 NEAs over 1 km. in diameter that orbit the Sun in trajectories that cross the Earth’s orbit. These orbit tracks shift around over time due to a number of gravitational perturbations and from time to time intersect the orbit of the Earth. On rare, but statistically predictable occasion, the Earth and the NEA 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 NEA 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 NEA 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 tug-boat with the assignment of rendezvousing with our pending visitor, snuggling up against it and pushing it gently, but steadily. Pushing against a NEA for a year or more with just a few pounds of force will be enough to change its velocity by 10 cm/sec or greater. This is enough to cause the NEA, 10 years later to miss the Earth vs. pay us a direct visit.
The rub, of course, is that we are currently only detecting and tracking the big, civilization destroyers, the NEAs 1 km. in diameter and larger which hit us, on average, every several million years. We now know of and track about 75% of these large objects. It is, however, the hundreds of thousands of smaller asteroids between 100 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 NEA 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.
So if we are to act responsibly we must first detect and track these smaller NEAs in order to provide ourselves adequate warning time. Then, after detecting an unwanted visitors we would launch a space tugboat on a mission 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 shift the current detection emphasis downward to NEAs of about 100 meters in diameter. There is, however, virtually no effort being made to develop the technology necessary for the tugboat/deflector.
Hence the purpose of the B612 Project, for which I serve as Chairman of the Board, is to demonstrate the ability to alter the trajectory of a small asteroid by actually doing it. We all know that the best way to learn how to do something is to do it. Therefore the stated goal of the B612 Foundation, is to significantly alter the orbit of an asteroid in a controlled manner by 2015.
Good luck, right? Feel free to join in. Nothing like being part of the largest environmental project of all time!
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