NEO News: Spaceguard Survey of Near Earth Asteroids

I am delighted to report that the Spaceguard Survey, which has the
objective of finding 90% of the NEAs larger than 1 km diameter
(defined as brighter than absolute magnitude H = 18) by 2009, is now
approximately half complete (measured by number of objects, not by
time to complete) Through the end of June 2000, 410 of these larger
NEAs have been found. Recent estimates of the total population of
these larger NEAs are somewhat less than 1000. If we take the recent
published estimate by Bottke and colleagues of 900 as representative,
then the objective of the Spaceguard Survey would be to discover 90%
of 900, or 810, NEAs by 2009. The current known number of 410 thus
slightly exceeds this half-way milestone. Of course, the total
number of NEAs of 1 km or larger diameter is only an estimate, with
considerable uncertainty. However, it is clear that even with this
uncertainty, we are at lest closely approaching the half-way mark.
Congratulations to all concerned!

This information is contained in a recently circulated report from
Don Yeomans of JPL, the head of the NASA NEO Program Office. Don has
prepared some very nice color charts to illustrate the current status
of the search, which are included in this part 2 of NEO News.

Yeomans also shows the observatories that are making these NEA
discoveries. The MIT LINEAR system operated by Grant Stokes
continues to dominate the discovery statistics. Following are the
numbers of discoveries of the larger NEAs for the past 5 half-year
intervals:

Date		98-1	98-2	99-1	99-2	00-1

LINEAR		11	29	22	29	41

All others	 9	10	12	 7	12

Total		20	39	34	36	53

Don’s message with the charts follows.

David Morrison

David Morrison, NASA Ames Research Center

Tel 650 604 5094; Fax 650 604 1165

david.morrison@arc.nasa.gov or dmorrison@mail.arc.nasa.gov

website: http://space.arc.nasa.gov

website: http://astrobiology.arc.nasa.gov

website: http://impact.arc.nasa.gov

Dear Colleagues,

The attached charts show the progress being made in achieving
the NASA goal of discovering 90% of the Near-Earth Asteroids (NEAs)
(larger than 1 km) in ten years.

The first chart shows the recent progress toward discovering the
total population of large NEAs. The horizontal lines indicate the
approximate limits on the estimates for the total population of large
NEAs. A recent study by Bottke et al. suggests that the total
population of large NEAs is about 900.

The second chart shows the contribution of each of the NASA funded
programs to these discoveries. Clearly the LINEAR program is making
most of the discoveries of large NEAs. The third chart shows the
total number of large NEAs discovered as a function of time and the
same information for all the NEAs (regardless of size). The 4th
chart is similar to the second except that the discoveries of all
NEAs (regardless of size) are give for each NASA supported search team.

With kind regards,

Donald K. Yeomans

Supervisor, Solar System Dynamics Group

Jet Propulsion Laboratory

301-150

Pasadena, CA 91109

Tel. (818) 354-2127

FAX (818) 393-1159

Dear Friends and Students of NEOs:

Two days ago I circulated the information (received from Don Yeomans)
that the Spaceguard Survey is at, or at least very near to, the
half-way point toward discovering 90% of the NEOs larger than 1 km in
diameter. As of the end of June, 410 NEOs were known brighter than
absolute magnitude H = 18.0. Subsequent e-mail discussion has
focused on when the Spaceguard Survey really began, and how long it
will take to complete it.

In summary: The NASA commitment to carry out the Spaceguard Survey
(to 90% completeness in ten years) was made in May 1998. Thus the
goal against which to measure progress should probably be 90%
completion by the beginning of 2008. At the current rate of
discovery, it is estimated that we will reach reach this goal around
2015. An increase of a factor of 2-3 in discovery rate would be
required to meet the 2008 goal. It is not clear how we might achieve
this improvement, however. It may not be possible to probe faint
enough with 1 m telescopes, but the alternative construction of new 2
m telescopes would take such a long time that the survey completion
date would probably not actually be moved that much closer.

These ideas are amplified in the e-mail messages quoted below.

David Morrison

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To David Morrison from Alan Harris:

Your “half way” cheering is a bit overstated on both ends, I think.
Even if you extrapolate the current rate back to zero objects you
place us about 4 years into the survey (400 objects at ~90/year). So
when does the clock really start? I would say around 1997 or 1998
latest. By the way, over the last 12 months, my score is 90
discoveries, or 7.5/month. During the latest year then, there were
900 – 350 = 550 “targets” out there, of which 90 were found. That
makes the e-folding time for discoveries 550/90 = 8 years. To get to
90% from where we are now assuming an exponential completion curve
will take 16 years (starting from last year), or to 2015. So, even
accepting the new lower population, we are only discovering half fast
enough to make the goal. And allowing for the non-exponential shape
of the discovery curve from my models, we are actually a factor of 3
or so short of the rate needed to achieve the goal. But does it
matter? Is 15 years from now rather than ten years from a couple
years ago acceptable? I suppose that depends on what lurks out there
with our name and a year between 2009 and 2015 on it. All this may
be academic in the context of
the originally stated goal, since building new multi-meter telescopes
will take longer than just waiting for LINEAR to finish the job.

——————————————–

To Alan Harris from David Morrison

You ask: when did the 10-year Spaceguard Survey time-period begin?
Here is the history as I remember it. The “ten year” number (which
was originally for a “complete” NEA survey but which we interpret as
90% completeness in ten years, since the survey is never really
“complete”) originated in the U.S. Congress request made in 1994
during the week of the S-L 9 impact with Jupiter. How to meet this
requirement was the focus of the NASA Shoemaker Committee
deliberations, which led to a report to NASA/OSS in mid-1995. As you
recall (as a member of that committee), NASA effectively rejected the
recommendations of the Shoemaker report in its cover letter sent to
the Congress in 1995. However, work continued, and in early 1998 (at
about the time of the FX11 false alarm and the several TV
documentaries on the impact hazard, such as the one done by National
Geographic) NASA responded. I’m not sure of the exact sequence, but
1998 saw the Houston meeting with Tom Morgan and Carl Pilcher, a
Congressional hearing at which NASA committed to raise the NEA search
budget to about $3.5M/yr, formation of the NEO Program Office at JPL,
and initiation of formal high-level meetings between NASA and the
USAF on cooperation in NEO search and related studies. It seems to
me that these actions taken in 1998 constituted a NASA commitment to
the Spaceguard goal. This commitment was reiterated at the time of
the Torino IMPACT meeting in June 1999, when Carl Pilcher, Tom Morgan
and Don Yeomans all stated in one form or another that the Spaceguard
Survey was underway and the ten-year clock had begun.

———————————————

To David Morrison & Al Harris from Clark Chapman:

The following text is the conclusion of Carl Pilcher’s Congressional
testimony before the House Space and Aeronautics Subcommittee on May
21, 1998, and clearly commits NASA to achieving the goal, as usually
stated, within ten years
(I would assume from that date).

CONCLUDING REMARKS

The issues and challenges posed by NEOs are inherently international,
and any comprehensive approach to addressing them must be
international as well. Central areas of concern include coordination
among NEO observers and orbit calculators around the globe and public
notification should an object posing a significant hazard to Earth be
discovered. NASA has begun discussing, with the international
community, convening an international workshop to address these
issues. The workshop will likely be held during the first half of
1999. The goal of this workshop will be to develop international
procedures and lines of communication to ensure that the best
available accurate information about any potentially hazardous object
is assembled and disseminated to the public in the shortest possible
time.

To facilitate coordination among NASA-supported researchers, other
agencies and scientists, and the international community, NASA is
establishing an NEO Program Office. This Office will coordinate
ground-based observations, ensure that calculated orbital elements
for NEOs are based on the best available data and support NASA
Headquarters in the continuing development of strategies for the
exploration and characterization of NEOs. In the unlikely event that
a potentially hazardous object is detected, the Office would
coordinate the notification of both the observing community and the
public of any potentially hazardous objects discovered.

NASA is committed to achieving the goal of detecting and cataloging
90% of NEOs larger than 1 km in diameter within 10 years, and to
characterizing a sample of these objects. We are developing and
building instruments, and developing partnerships — particularly
with the Air Force — which should lead to the necessary detection
and cataloging capability being in place in 1-2 years. This
capability will also allow us to detect and characterize many NEOs
smaller than 1 km.

In summary, NASA’s obligation and commitment is to ensure that we
have the information necessary to understand the hazards posed by
NEOs.

Carl B. Pilcher

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