Mathematics – Probability
Scientific paper
May 2010
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010dda....41.0602g&link_type=abstract
American Astronomical Society, DDA meeting #41, #6.02; Bulletin of the American Astronomical Society, Vol. 41, p.931
Mathematics
Probability
Scientific paper
Radar measurement of distance (to tens of meters) and velocity (to millimeters per second) have been reported for 237 of the 380 asteroids and comets detected by radar since 1968. Some 86% of the cases have been within the last 15 years. To characterize the effect of radar astrometry, a debiased population was used to assess detectability, trajectory prediction, and physical characterization capabilities of the existing Goldstone and Arecibo sites and potential upgrades. It was found that existing planetary radar installations can detect 69-98% of the potential impactors (70 <= d <= 700 m) more than a year before impact, once optically discovered. Radar astrometry increases the mean Earth-encounter predictability interval from 80 to 400 years, increases impact warning an average of up to 4 years, and can potentially image 22% of the d > 140-m population at few-meter levels (comparable to a spacecraft flyby mission), identifying targets of interest for future missions. Such physical characterization is a prerequisite for accurate heliocentric trajectory predictions and thus meaningful calculations of impact probability for those km-size and smaller NEAs having a close planetary encounter prior to a potential impact in subsequent years. For such cases, having unknown trajectory prediction model biases comparable in size to the measurement uncertainties they are superimposed on, a deterministic single-value estimate of impact probability may not be a useful indicator. The situation can instead be represented with a probability range Ip= [Ip_min, Ip_max], or as error-bars with respect to the standard dynamical model estimate, Ip= Ip_std +/- x1,x2 where x1= (Ip_max - Ip_std) and x2= (Ip_std - Ip_min).
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