[meteorite-list] Progress in the Spaceguard Survey

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu Apr 22 09:54:02 2004
Message-ID: <200202092239.OAA27774_at_zagami.jpl.nasa.gov>

http://web99.arc.nasa.gov/impact/news_detail.cfm?ID=109

Progress in the Spaceguard Survey
Alan Harris (JPL) and David Morrison (NASA Ames)
February 2, 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)


       LINEAR LONEOS NEAT-M NEAT-P SW-I SW-II Other | Total

Jan 22 6 1 0 3 0 - - 1 0 - - 0 0 | 27 6
Feb 19 6 1 0 2 1 - - 1 0 - - 0 0 | 23 7
Mar 15 5 8 0 4 1 - - 1 0 - - 2 0 | 30 7
Apr 12 3 6 1 2 1 - - 2 0 - - 0 0 | 22 5
May 11 3 4 2 7 3 5 1 2 0 - - 0 0 | 29 9
Jun 9 4 2 1 0 0 5 3 0 0 - - 0 0 | 16 8
Jul 1 0 5 2 3 0 13 4 0 0 - - 0 0 | 22 6
Aug 18 4 3 2 7 3 12 1 3 0 - - 0 0 | 43 10
Sep 47 17 10 2 0 0 7 2 1 0 - - 0 0 | 65 21
Oct 35 4 0 0 3 0 11 1 4 0 2 0 0 0 | 55 5
Nov 35 7 3 1 1 0 2 0 1 0 3 0 0 0 | 45 8
Dec 45 8 2 0 2 1 4 1 1 0 0 0 2 0 | 56 11
Jan 48 13 1 1 4 0 4 1 3 0 0 0 1 1 | 61 16
------------------------------------------------------------|--------
Tot 317 80 46 13 38 10 63 14 20 0 5 0 5 2 | 494 119


The next table groups the discoveries into 6-month intervals for
easier comparison with earlier years. It also drops the final
lunation:


        LINEAR LONEOS NEAT SpacewatchOther Total

01-1 88 27 22 4 28 10 7 0 2 0 147 41

01-2 181 40 23 7 65 13 15 0 2 0 286 60
-----------------------------------------------------------------
Tot 269 67 45 11 93 23 22 0 4 0 433 101


It is particularly notable how much LINEAR's discovery rate picked up
in the second half of the year. A preliminary look at discovery
magnitudes suggests this is largely due to reaching to fainter
magnitude, around visual magnitude V=19.5, while previously the limit
was near V=19.0. Both NEAT systems are getting down to around V=19.5
too. It is this improvement in the detection limits that keeps the
discovery rate so high; without such improvements we would expect a
drop-off as the survey becomes more complete. The average discovery
rate for 2002 is 9 per lunation, approximately the same as in 2000
(10 per 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. 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.
Received on Sat 09 Feb 2002 05:39:39 PM PST