NEO News: Spaceguard Survey of Near Earth Asteroids

Dear Friends and Students of NEOs:

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

chart 1

chart 2

chart 3

chart 4


NEO News (8/3/00) More on Spaceguard

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.

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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.

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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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