NEO News: Spaceguard: How Are We Doing?

Alan Harris (JPL) and David Morrison (NASA Ames)

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

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.