Statistics – Computation
Scientific paper
Jan 2012
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2012aas...21912202c&link_type=abstract
American Astronomical Society, AAS Meeting #219, #122.02
Statistics
Computation
Scientific paper
Asteroid impact hazard monitoring has so far focused primarily on warning of potential impact threats within the next century. This 100-year search horizon is generally appropriate because impact mitigation efforts over longer time horizons are often precluded due to low impact probabilities associated with long-term predictions. Moreover, searching farther into the future for potential impacts is problematic, first because the fractal nature of keyholes means that most recent asteroid discoveries harbor a cascade of many very low probability events beyond several decades in the future, leading to a significant increase in computational cost for longer searches. But more importantly, the standard theories used in the current impact monitoring systems become inadequate for longer search intervals.
Well-observed asteroids with high-precision orbits represent a different class of object for impact monitoring. In these cases the future trajectory may be well known for a long period, a century or more, until the object has a close planetary encounter that scatters the range of possible trajectories, thereby injecting a large amount of uncertainty. At that future point the problem can become similar to that of a newly discovered asteroid, with a wide range of future trajectories. Nongravitational accelerations, namely the Yarkovsky Effect, can also become an important consideration. Assessing the uncertainty due to the Yarkovsky effect can be difficult, especially when the spin state of the object is not known, and yet reasonable assumptions can be followed to estimate the dispersion due to this effect. In many high precision cases the Yarkovsky spreading remains small relative to the dispersions due to planetary encounters and so it can be neglected. But when the uncertainty due to the Yarkovsky Effect is large enough to significantly alter the circumstances of a planetary encounter it must be incorporated into the impact assessment.
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