NEO News Survey status 20 Jan 2001

Dear Friends and Students of NEOs:

This edition of NEO News contains the annual summary of progress
toward the Spaceguard goal of finding 90% of the Near Earth Asteroids
(NEAs) brighter than absolute magnitude 18 (corresponding to diameter
of 1 km) by 2008. I am grateful to Don Yeomans and Alan Harris of JPL
for this information. As of the end of 2000, we are more than halfway
to this goal in terms of numbers, but not in terms of required time
and effort.

Let me also take this opportunity to call to your attention the
bibliography of technical publications dealing with NEOs and the
impact hazard. This listing, beginning with 1992, is found on the
NASA impact hazard webpage (impact.arc.nasa.gov). I have recently
updated the bibliography by adding publications from 1999 and 2000.
The annual rate of publication continues to grow as this field of
study attracts more and more scientific attention.

David Morrison

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THE STATUS OF THE SPACEGUARD SURVEY, JANUARY 2001

David Morrison

Alan Harris

Don Yeomans

During 2000 (up to January 8, 2001, to cover the final observing
month in full), 125 NEAs of absolute magnitude H < 18.0 were discovered, or ~10.5/month, from the tabulation by Harris. This is up from around 7.5/month the previous year. The total numbers to date (Jan 08) are N(all) = 1254, N(H<18) = 467. Following is a listing of the monthly (by lunation) discoveries of H < 18 and all. The dates correspond to new moon each month:

   date  N(H<18)  N(all)
2000.01    6      19
2000.10   10      28
2000.18   16      40
2000.26   12      30
2000.34    9      25
2000.42    6      21
2000.50    5       7
2000.58   12      29
2000.66   10      35
2000.74    9      43
2000.82   10      24
2000.90   13      43
2000.98   10      27

The above listing includes quite a few relatively bright (large)
NEAs. This year’s discoveries include 4 NEAs with H between 13 and
14, 8 NEAs with H between 14 and 15, and 18 NEAs with H between 15
and 16. The dozen discoveries of new NEAs brighter than H = 15 are in
a size range that was thought (on some models) to be already nearly
complete.

The following breakdown by discovery team refers only to the calendar
year 2000 ending on December 31. Of the 109 new NEAs brighter than H
= 18 listed by Yeomans, 82 (75%) were discovered by the LINEAR
program using two USAF telescopes in New Mexico, with 8 (7%) by the
second-ranking LONEOS program at Lowell Observatory in Arizona. A
number of additional smaller search programs contributed the
remaining 18% of discoveries.

Harris has carried out an analysis of the rate of rediscoveries from
LINEAR to estimate the total population of NEAs as a function of
size. The resulting estimate is slightly more than 800 brighter than
H = 18, consistent with several other recent estimates in the 800-900
range. However, Harris notes that such estimates based on rediscovery
will always yield a lower bound for the total numbers, since they
implicitly assume that the undiscovered population is similar to the
discovered population. Thus any groups of NEAs that is more difficult
to detect will be underestimated in the total just as they are
undercounted in the observed population. Therefore the true total
number of NEAs down to 1 km diameter is probably as high as 1000.
Also note, however, that the statistically undercounted groups (those
with orbits that don’t bring them close to the Earth as often) are
also probably less important in terms of the impact hazard than are
the groups that do often come close. Finally, note that we continue
to discover larger NEAs where the standard models indicate that we
should have a nearly complete listing. The point of this complicated
discussion is that estimating total populations is complex,
especially if we are primarily interested in those NEAs that pose a
potential impact hazard to the Earth. The calculations by Harris will
appear in a future issue of Icarus.

If we adopt an estimate of 1000 NEAs larger than 1 km, then we have
now found 47%. If the true number is nearer 900, as indicated by
recent estimates, then we now have 52% in our NEA catalogues. Either
way, we are clearly beyond the halfway mark to the goal of finding
90% by 2008.

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NEO News is an informal compilation of news and opinion dealing with
Near Earth Objects (NEOs) and their impacts. These opinions are the
responsibility of the individual authors and do not represent the
positions of NASA, the International Astronomical Union, or any other
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dmorrison@arc.nasa.gov. For additional information, please see the
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