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Posted by: dilo Aug 5 2006, 10:47 AM

Looking to last http://neo.jpl.nasa.gov/stats/ data, there was a dramatic decrease of new big NEA discovery rate in the last 6 months (they almost halved). Even more impressive, the number of big PHA (objects really close Earth orbit) remained stable in the last 7 months, while increased at average rate of 1 per month previously.
This is not unexpected, the search for these object has seriously started 8 years ago and the goal was to catch 90% of total population within 10 years. The fact that, in spite of the ever increasing search effort, discovery rate reached maximum in 2002 and now is decreasing suggests that census is nearing the saturation.
I made a very simplified attempt to estimate the total number of these objects based on actual discovery trend,modeling the cumulative curves of PHA/NEA greater than 1Km for the last years:

The interpolated curves are typical saturation trends in the form: N=A(1-exp(-(time- B)/C)) where C is a time constant resulting equal to 3 years in both curves. The constant A tell us the total population number, and the reported curves correspond to 945 NEA and 183 PHA.
If true, this means that we already discovered 87% and 89% of total PHA/NEA populations, respectively!
Obviously, the search will continue on the ever increasing population of smaller objects, not a threat for the planet but for local heavy damage...

Posted by: dilo Jan 11 2007, 09:21 PM

Time to update.
There was a substantial change in the number of dangerous asteroids reported in the NASA http://neo.jpl.nasa.gov/stats/ (-18%) due to revised size:
"The Until relatively recently, the mean albedo for NEAs was thought to be 0.11 so the corresponding absolute magnitude for a NEA whose effective diameter is one kilometer was thought to be H = 18.0.
[...]
Recent work by Stuart (2003) and others have shown that NEAs are, in the mean, 20% brighter than previously thought so that the mean albedo for NEAs is 0.14 rather than 0.11. Using this revised mean albedo implies the absolute magnitude (H) for a NEA with an effective one kilometer diameter is 17.75."

This brought to a revised estimation with criteria disussed above: the total number of NEA>1Km should become close to 776 and PHA are 150 or slightly below...

Posted by: elakdawalla Jan 11 2007, 09:25 PM

Huh. Good catch on that update, Dilo.

--Emily