From: Ames Research Center
Posted: Saturday, February 9, 2002
We have now found 587 of the larger (1 km) NEAs. Will we make the goal of 90% completeness by 2008?
The Spaceguard Goal as adopted by NASA is to discover 90% of the near Earth asteroids (NEAs) larger than 1 km (actually, brighter than absolute magnitude H=18) before the end of 2008. This is a summary of progress through the end of 2001, with more than 100 new discoveries of NEAs brighter than H=18, bringing the total to 587 as of January 28, 2002. The total number of known NEAs of all sizes is 1743.
The following table shows the discoveries of total NEAs and of NEAs brighter than H=18, listed by month and observing team during 2001. The months are actually lunations, full moon to full moon, starting with the full moon of January 9 2001, and ending with the full moon of January 28, 2002, a total of 13 "months." The observing groups listed are LINEAR (MIT), LONEOS (Lowell Observatory), NEAT-Maui (JPL), NEAT-Palomar (JPL; new), Spacewatch-I (Kitt Peak), and Spacewatch-II (Kitt Peak; new)
The next table groups the discoveries into 6-month intervals for easier comparison with earlier years. It also drops the final lunation.
We can also ask how long it will take at the present discovery rate to find 90% of the NEAs brighter than H=18. The present total number of discovered NEAs of H = 18.0 is 587. Taking a nominal value of 1000 as the total population, that implies that the survey is now 59% complete, with a target of 90% completion by 2008. It appears that, especially if the discovery efficiency of the last 5 months can be sustained, the Spaceguard Survey may be on track for 90% completion by 2008 or 2009. However, this statement is dependant on what number is assumed for the total population, since the discovery rate needed to finish the job depends on the number of objects remaining to be discovered. For example, if the total population is only 800 (we consider this impossibly low, but is still 100 above one of the estimates of two years ago), then 90% completion requires discovering only 133 more objects. For an assumed population of 1000, we need 313 more discoveries to reach 90%, and for an assumed population of 1200, an additional 493 discoveries are needed to achieve 90% completion.
We may be still a little shy of the mark for 90% completion by the end of 2008, but not seriously so for the nominal population of 1000. If there are as many as 1200, then we will have to go deeper (perhaps beyond magnitude V=20) to reach the goal in 2008. Or we would need to increase sky coverage, for example by adding a telescope at a Southern Hemisphere site whose long winter nights (hopefully clear) would complement the short and often cloudy summer nights in the US Southwest.
Detailed modeling of the survey and analysis of the discovery statistics is in preparation by Harris and will be published later in the professional literature.
Alan Harris (JPL) and David Morrison (NASA Ames), 02/02/02
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