Invited Paper IPF-TuA10
Understanding the Near Earth Object Population

Tuesday, October 16, 2007, 4:40 pm, Room 602/603

Near Earth Objects (NEOs) are asteroids and comets on orbits that allow them to approach and, in some cases, strike the Earth. This population is comprised of bodies ranging in size from dust-sized fragments to objects tens of km in diameter. It is now recognized that the impact of diameter D > 0.1 km NEOs represent a small but non-negligible hazard to human life and infrastructure. Interestingly, however, the potential threat represented by these bodies may also be one of easier ones to mitigate against, provided adequate resources are allocated to identify all of the NEOs of relevant size. Using our knowledge of the collisional and dynamical mechanisms that transport asteroids and comets from their source regions all the way to NEO space, we now have a working model of the steady-state orbital, size, and albedo distributions of the NEO population. This model does an excellent job of reproducing observations from various NEO surveys (e.g., LINEAR). We predict the existence of approximately 1000 NEOs that are roughly 1 km in size. The mean impact interval for these objects with the Earth is 0.5 My, with most impactors being asteroids rather than comets. We also find that the Earth should undergo a 1000 megaton (MT) collision every 64,000 years. Only a tiny fraction of the 300 m diameter bodies capable of producing these kinds of blasts have been discovered to date. These predicted impact rates are in good agreement with the terrestrial and lunar crater record and have been confirmed by recent work. Our NEO model has recently been used to predict the future rate of NEO discoveries using current and next-generation survey technology. We find that 90% of the potentially hazardous (diameter D > 140 m) NEOs could be found within 20 years or so using new ground- or space-based surveys. The cost of these systems vary, but much can be accomplished for a budgetary equivalent to a NASA Discovery-class mission ($200-$400 million). Our understanding of the processes that produce NEOs has also led to new insights into how the terrestrial impact flux has changed over time. We can now show that large breakup events in the inner portion of the main asteroid belt may trigger so-called asteroid showers, events that can dramatically increase the impact flux on Earth for prolonged periods (e.g., in some cases for as long as 100 My). In fact, one particular breakup event occurring within the last 200 My may have had important implications for our understanding of mass extinction events and life on Earth.