|The rocks inside a crater on the Asteroid Eros, as imaged before impact with the NEAR spacecraft. Numerous small impacts on the asteroid show brown boulders visible interior to the less exposed (white) lip of the crater. False-color for emphasis.
Image Credit: NASA/Eros
Russell Schweikart is the Chairman of the B612 Foundation, an advocacy group endorsing 'a gentle push' approach to asteroid risk mitigation. Schweikart was also an Apollo 9 astronaut and uses his experiences in mission planning to design a strategy for diverting incoming --and potentially life-threatening--space debris. The B612 Foundation's charter proposes a demonstration to alter the trajectory of an asteroid in a controlled manner by 2015.
The origin of the foundation's name, B612, stretches back into historical literature. B162 was the asteroidal address for The Little Prince, authored by the French writer Antoine de Saint Exupery in 1943. Their call for action is founded on four principles: asteroids have led to planet-scale disasters historically, a sea of near-earth asteroids surrounds us, an unacceptable collision this century carries a two-percent risk, and actions to avert a collision should be started now. To astrobiologists familiar with the geological record, asteroids and comets have shaped our own planet's biology, but are best preserved in the geological records among the craters on neighboring moons and planets.
Schweikart recently summarized his concerns in a white paper entitled, "The Need for a UN Asteroid Deflection Treaty", portions of which are edited into a question and answer format for presentation here. A central premise of the tugboat strategy is to understand what happens when a rubble of rocks gets pushed in space and then to gauge our own reactions to the good or bad news.
Astrobiology Magazine (AM): What is the status on the Spaceguard program?
Russell Schweikart (RS): The Spaceguard Survey 2, involving astronomers and observatories around the world, is detecting new near Earth objects (NEOs) at a current rate of about 10 per week. NASA, in testimony before the US Congress, committed to the goal of detecting 90% of NEOs greater than 1 km. in diameter before the end of 2008. Over 640 of an anticipated total population of 1000-1100 have now been detected.
AM: What size ranges are threatening in a collision?
|The painting titled "K/T Hit" by artist Donald E. Davis. This impact occured 65 million years ago, ending the reign of the dinosaurs.
Image Credit: Don Davis
RS: While a collision with an asteroid of 1 km. or larger would threaten human civilization, collisions with asteroids smaller by a factor of 10 would be substantial and threaten local and regional populations. A 100 meter diameter asteroid would have the equivalent impact energy of a 100 megaton nuclear weapon. Since the expected population of NEOs of this size is approximately 200,000 the collision rate is considerably higher than those that threaten society as a whole. An impact by a 100 meter NEO is anticipated on the order of every 2-4000 years.
AM: What exactly happens when a new object is found near us today?
RS: Optical telescopes designed for survey purposes generally perform the initial detection of NEOs. Confirmation of these initial findings and refinement of the orbits by subsequent optical measurements are performed by a combination of professional and amateur astronomers on a worldwide basis. Generally, within a matter of weeks following initial detection, the orbital parameters of a newly detected NEO are well enough known to determine whether a collision is to be expected within the next 100 years.
Active radar is being used with increasing frequency to investigate the physical characteristics of known NEOs and to significantly increase the precision of the knowledge of their orbits. Radar data typically reduce the positional errors in NEO orbit predictions by several orders of magnitude, allowing impact predictions to be reliably forecast out to several hundred years.
AM: Once a collision is predicted, what recourse is available?
RS: Active systems for deflection of NEOs on collision courses with Earth have been casually discussed for several decades. Little substantial work, however, has been done to date.
AM: Are there alternative to those shown in films like "Armageddon" and "Deep Impact"?
|Impact of the Tunguska explosion is visible even after 90 years.
Credit: Galena HS
RS: Detonating a nuclear explosion in the near vicinity of a NEO would create an impulse slightly deflecting the object from its undisturbed path, and may be the only available technique for short warning times. For the expected warning times of a decade or more, however, concerns about the abuse of nuclear weapons in space and the multitude of uncertainties about the response of the NEO to the explosion have triggered strong objections to this proposal
AM: The B162 Foundation has advocated for low-thrust deflections. Can you elaborate on how it might work?
RS: Using low levels of thrust for long periods of time can generate enough velocity change to cause the NEO to miss the Earth. These systems assume that a decade or more of warning time will be available in order to permit the successful deployment, rendezvous and deflection time required to achieve the planned result. In many instances, whether utilizing an indirect, stand-off system (mirror, laser, etc.) to boil off surface material, or direct thrusting by a docked system (mass driver, plasma engine, etc.), the thrusting technique requires a year or more of continuous application to achieve the necessary velocity change.
These low thrust systems appear to have the additional advantage that the extremely low accelerations involved are not likely to disrupt the integrity of the NEO. This concern has emerged recently with the recognition that many of these objects are extremely tenuous. Indeed, some recently characterized NEOs appear more to be closely associated piles of rubble than solid bodies. Very low acceleration deflection systems, therefore, appear to be desirable.
AM: With a year of thrust applied slowly, the asteroid tracks across different places on Earth. Are there issues with targeting in the international arena?
RS: Clearly the question of how this path is chosen and how and by whom the agreed thrust profile is executed is of enormous local and international import.
|Simulated perspective view from asteroid surface looking towards Earth.
Since the possibility of propulsion system failure exists throughout the deflection operation, the resultant new impact point will have been defined by human choice and not by an "act of God". In fact, during such a deflection operation all points along the resultant path will be placed at some increased risk during the operation due to, inter alia, potential propulsion system failure.
Indeed, choosing a slightly modified (non-optimal) thrust profile might enable the path to either miss, or cross over, a given country on its way to the liftoff point. Since the initial deterministic point of impact, and to a lesser extent, the risk path from there to liftoff, could cross any point on the planet, it is assumed that this international agreement would be established under United Nations auspices.
AM: What are the implications for science planning in a global political choice?
RS: It takes little imagination to visualize the extreme political and social controversy if we wait for a specific impact to become known before developing the path deviation criteria.
|Artist's depiction of the Chicxulub impact crater. Credit: NASA
The opportunity for abuse and the underlying human characteristics that concerned Carl Sagan (when he reflected in 1992 on potential "negligence, fanaticism or madness") still remain a challenge while the instantaneous impact point is slowly guided off the Earth. This deflection dilemma arises in the recognition that if one can deflect an incoming NEO such that it misses the Earth, one can as well deflect a NEO that would otherwise miss the Earth such that it now hits the Earth, presumably in a particular location.
While I consider this historic dilemma to be virtually non-existent there exists a "real" and significant deflection dilemma that cannot be avoided if the Earth is ever to be protected from asteroid impact. The dilemma arises in the Hobson's choice between doing nothing, thereby suffering the consequences of an impact, or pro-actively deflecting an asteroid which will, in the process of "protecting the Earth", necessarily place otherwise non-threatened people and property at risk.
This is clearly a challenging task since the few space faring nations of the world are powerful, and such intrusive oversight will not be easily negotiated. It is crucial to realize that the appropriate time-window to negotiate these international agreements is not the time available until an impact occurs, but rather the time available until an impact is predicted.
AM: What is the significance of the date in the next decade, 2015?
RS: This is clearly a judgment call, but we believe, from the assessment we've done, that the technologies and techniques required can be developed to meet that timeframe. Everyone in the engineering world knows that selecting too long a timeline does not generally end up with a better system. Conversely it does generally mean that the system developed is more costly. At the other extreme, having too short a timeline will guarantee failure and waste of money.
The challenge is to select a reasonable timeline that enables the job to be done, but not with so much slack that the "better" continually replaces the "good enough".
The B612 Foundation is a California non-profit private foundation with the goal of altering the orbit of an asteroid in a controlled manner by 2015. The B612 project grew out of a one-day workshop on asteroid deflection, organized by Princeton astrophysicist Piet Hut and astronaut Ed Lu at NASA Johnson Space Center, Houston, Texas, on October 20, 2001. Participants Rusty Schweickart, Clark Chapman, Piet Hut, and Ed Lu established the B612 Foundation on October 7, 2002.
Related Web Pages
Great Impact: Part I: The Benefits of Hard Bodies
Great Impact: Part II: Much Ado about Nothing?
Great Impact: Part III: The Large and the Small
Great Impact: Part IV: On A Collision Course with Earth
Great Impact: Part V: Encore
Impact Hazards Website
NASA/JPL Near Earth Object Program
IAU Minor Planet Center