Astronomy and Astrophysics – Astronomy
Scientific paper
Oct 2007
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007dps....39.5001h&link_type=abstract
American Astronomical Society, DPS meeting #39, #50.01; Bulletin of the American Astronomical Society, Vol. 39, p.511
Astronomy and Astrophysics
Astronomy
2
Scientific paper
I have used three overlapping methods to estimate the population of NEAs. In the largest size range, to about H = 16, current surveys are sensibly complete, so the discovered numbers anchor the population at the large end. In the intermediate range, to about H = 20, I have estimated the fraction of completeness from the ratio of re-detections of already known NEAs to the total number of re-detections plus new discoveries in the interval 2005+2006. The re-detection ratio is bias-corrected using a survey simulation model to allow for the fact that NEAs are not equally easy to detect. Finally, the relative completion can be extended to the smallest sizes using the same survey simulation model to estimate the relative detection efficiency vs. size. The resulting size-frequency distribution deviates substantially from a constant power law with diameter in the size range from 1 km down to 10 m, with as much as a factor of several fewer NEAs in the range 100 m compared to a straight power law. The maximum "dip" in the distribution corresponds to the size of transition from "rubble pile" to "monolithic" bodies, and may be related to this transition. The impact risk from NEAs smaller than 1 km diameter is several times less than previously estimated. Current surveys are 75% complete down to a size of 1 km (H < 17.75), as of the end of 2006. As a result, the short-term impact risk (this century), mostly from large impacts, has been reduced by an order of magnitude compared to the a priori impact risk, since those discovered to date pose negligible impact risk in the near future.
This study was sponsored by the NASA Near Earth Objects Observation Program through the JPL NEO Program Office.
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