... world governments must take the threat of NEO impacts seriously and must support actions that lead to the development of credible defensive capabilities.
Session 9: Asteroids Impacts
Wednesday 10 December 2003
Time: 10:30-12:00
Chair: Jean-Marc Sibeaud /Walter Flury
10:30 Two and Three Dimensional Simulations of Asteroid Ocean Impact
Gisler, G.*; Weaver, R.*; Mader, C.* Gittings, M.**
*Los Alamos National Laboratory, **Science Applications International Corporation
10:50 Loading Sources for Seismological Investigations of Asteroids and Comets
Walker, J. Southwest Research Institute
11:10 Molecular Synthesis in Hypervelocity Impact Plasmas on the Primitive Earth and in Interstellar Clouds
Managadze, G*; Brinckerhoff, W.**; Chumikov, A.*
*Space Research Institute, Moscow; **John Hopkins University
11:30 Cometary Impacts into Ocean: Thermochemical Equilibrium Calculations of High Temperature Oxygen Generation on the Early Airless Earth
Premovic, P. University of Nis
Comment: This new report stresses the risk from small impactors around 150m in diameter. Based on the simulation software by John Lewis it is possible that this report underestimates the risk from slow-moving, shallow-angle or iron asteroids that penetrate deeper into the atmosphere and hence deliver more explosive energy to the ground. On the other hand, the risk from tsunami may be over-estimated.
Comment: A "scare" was unwarranted and there are the usual mis-informed headlines around the world. HOWEVER, observations made up to the time of the UK NEO news release had indicated that the chances of an impact in 2014 were about 1 in a million. This is slightly greater than the "background risk" of an undiscovered asteroid of similar size hitting us in the next 12 months. More recent follow-up observations have all but eliminated the risk of an impact in 2014. This is a large object (more than 1km across and capable of global environmental destruction  - see http://www4.tpg.com.au/users/horsts/climate.htm ). Also, for this size object, it is an unusually short "warning time" prior to a possible collision.
It is quite possible that it would have been detected in southern skies  several years ago if the Australian Spaceguard Survey had been in  operation (it was shut down in 1996). In any case southern sky observations over the past six years may have been useful for eliminating the threat (absence of an object in an image can assist in pinning down its orbit and eliminating a "virtual impact" prediction by the computer). (see http://www4.tpg.com.au/users/horsts/reading.html#iau for links)

"It's pretty much the only threat to human populations that could affect the whole planet," he says. "The tiny amounts of funding that go towards spotting asteroids and thinking about ways to deflect them just look woefully inadequate, whether you believe our impact rates or someone else's."

Phil Bland, New Scientist.

We write to you today as concerned citizens, convinced that the time has come for our nation to address comprehensively the impact threat from asteroids and comets. A growing body of scientific evidence shows that some of these celestial bodies, also known as Near Earth Objects (NEOs), pose a potentially devastating threat of collision with Earth, capable of causing widespread destruction and loss of life. The largest such impacts can not only threaten the survival of our nation, but even that of civilization itself.   

Although we are genuinely concerned about the NEO threat, none of us is an alarmist. We know of no Near Earth Object currently on a collision course with Earth, but science’s limited knowledge of the NEO population cannot rule out that possibility. Base on current information, a crisis response to these potential threats is not warranted.  That being said, however, based upon evidence of past impacts and recent asteroid observations as well as the possible consequences from just one relatively “small” NEO impact, “business as usual” regarding this threat is simply no longer a responsible or sensible course of action...

According to NASA, there may be as many as 100,000 NEOs with diameters of 100 yards or larger. Of those asteroids larger than 150 yards in diameter, about 250 are estimated to be potentially hazardous. The United States has very limited capability to detect these smaller NEOs, which can nevertheless inflict substantial damage upon striking Earth. There is a significant probability (20%) of such an object colliding with the Earth during the next century.   

Although the annual probability of a large NEO impact on Earth is relatively small, the results of such a collision would be catastrophic.  The physics of Earth’s surface and atmosphere impose natural upper limits on the destructive capacity of natural disasters, such as earthquakes, landslides, and storms. By contrast, the energy released by an NEO impact is limited only by the object’s mass and velocity.  Given our understanding of the devastating consequences to our planet and its people from such an event, (as well as the smaller-scale but still-damaging effects from smaller NEO impacts), our nation should act comprehensively and aggressively to address this threat. America’s efforts to predict, and then to avoid or mitigate such a threat should be at least commensurate with our national efforts to deal with more familiar terrestrial hazards...
We urge the Congress to call on this nation’s ready supply of talents and energies to responsibly address this threat. Our international partners also should be called upon to help meet this challenge, but the United States has a compelling responsibility to lead the way.

...Support for Southern Hemisphere search activities may further increase the discovery rate and should be expanded. Even when NASA achieves its current goal of identifying 90% of large NEOs, the undiscovered remainder will, of course, still pose a potential hazard. Congress should direct NASA to pursue the search for all such objects to statistical completion.