Dear Friends & Students of NEOs:
This edition of NEO News features a comprehensive summary from Don
Yeomans of the current status of NEA surveys (aka The Spaceguard
Survey). In addition, you will find below a short report on the UK
task group studying NEOs and the impact hazard, and a newspaper
account of a space telescope proposal being discussed in Canada
(taken from Benny Peiser's CCNet). It is interesting that a number
of recent space mission proposals have suggested contributions to NEO
searches as a justification, although in general these missions have
other primary targets and seem to add the NEO role as an afterthought.
David Morrison
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NEA SURVEY STATUS FROM DON YEOMANS
Minutes taken during the Near-Earth Object Observers meeting held
August 15, 2000 during the IAU General Assembly in Manchester England
This gathering was the second meeting of the Near-Earth Object (NEO)
observers to discuss efforts to maximize the NEO discovery rate among
the entire international observing community. The first meeting,
which included only the NASA supported search efforts, took place
September 20-21, 1999 at MIT's Lincoln Laboratory in Cambridge,
Massachusetts.
Don Yeomans opened the meeting at 11:00 and welcomed the community of
NEO observers and several interested IAU attendees. Yeomans noted
that the goal of this meeting was to discuss plans to maximize the
discovery rate of NEOs among the international community of NEO
observers and to investigate the extent to which coordination among
the various teams would help reach the Spaceguard goal. The
Spaceguard goal is to discover 90% of the near-Earth asteroids (NEAs)
larger than one kilometer within 10 years. The assumption is made
that a NEA with an absolute magnitude (H) less than 18.0 has a
diameter larger than one kilometer. Recent work by Rabinowitz et al.
(2000), Bottke et al. (2000), and Harris (2000) suggest that the
total population of near-Earth asteroids (NEAs) larger that one
kilometer (H < 18.0) is about 700, 900, and 1000 respectively. In an
earlier session of the IAU Working Group on NEOs (D. Morrison,
Chair), Yeomans presented charts that showed a dramatic increase in
the NEA discovery rate in recent years (over 400 NEAs larger than one
km through July 2000). During the same WGNEO meeting, Al Harris
presented his analysis suggesting that at the current rate of
discovery, the Spaceguard goal of discovering 90% of the NEAs larger
than one kilometer in ten years, would be reached not in 2009 but
rather in about 2015. Harris noted that to achieve the Spaceguard
Goal would require large NEA discoveries at roughly twice the current
rate. Hence we may be 40 - 50 % of the way toward meeting the
Spaceguard goal in terms of raw numbers, but certainly not in terms
of the time interval required.
Short status reports (see Appendix) were given by representatives of
the Japanese Spaceguard (S. Isobe), Catalina Sky Survey (S. Larson),
LINEAR (G. Stokes), LONEOS (E. Bowell), NEAT (E. Helin), and
Spacewatch (R. McMillan). Brian Marsden and Gareth Williams also
presented remarks from the perspective of the Minor Planet Center
(MPC).
After these short reports, the floor discussion began with Yeomans
noting the conclusions resulting from the earlier meeting (Sept.
1999) of the observers at MIT's Lincoln Lab could be summarized as
follows:
A. Effective coordination requires knowledge of each search program's
capability and capacity.
B. Each program needs to optimize and understand their own efforts
before attempting an inter-survey optimization.
C. Each survey program's sky coverage and limiting magnitude needs to
be well understood.
D. As a metric for gauging progress among the survey efforts, each
survey team needs to compute their search volume covered per unit
time.
E. Once each separate survey is internally optimized and once metrics
have been established for each survey, then monthly sky coverage
could be effectively divided up among the various surveys.
The following remarks represent the impressions of the undersigned as
a result of this meeting. These comments do not necessarily
represent a consensus view of the meeting participants.
Current survey efforts are posting the sky areas that they covered
the night before and this seems to be helping the plan to coordinate
the total effort. Because of the vagaries of weather, equipment,
personnel support, etc., this a posteriori posting of "where we've
been" is considerably easier to provide than an accurate a priori
posting of "where we'll look tonight." A truly integrated and
coordinated international program of a priori postings of planned
search areas will be difficult and, in any case, not realistic until
the above-mentioned points A-E are properly addressed. As the
separate survey efforts optimize their own techniques, and total
accessible sky coverage goes to deeper limiting magnitudes, the issue
of follow-up observations becomes more important. The search efforts
may soon evolve to a point where targeted follow up (most by
relatively small aperture telescopes) will be replaced by relatively
automatic inter survey follow-up as the same regions of sky are
searched more and more frequently by the various surveys. Gareth
Williams noted in his remarks that, to some extent, this automatic
follow-up between the various surveys is already taking place.
Don Yeomans
Manager, NASA Near-Earth Object Program Office
References:
Bottke, W.F. et al. (2000). Science, 288:2190.
Harris, A.W. (2000). Personnal communication. Manuscript by Werner,
Harris, Ivanov, and Harris in prep. for Icarus.
Rabinowitz, D.L. et al. (2000). Nature, 403:165.
---------------------------------------------------
Appendix: Short summaries of the status of the survey efforts.
Japanese Spaceguard (S. Isobe):
Located at Bisei town Japan, the Japanese Spaceguard program will
consist of two optical telescopes for the detection of near-Earth
objects and space debris in Earth orbit. The 0.5 m telescope, in
operation since February 2000, has a field of view of 2 square
degrees (f/1.9) and uses a CCD array consisting of two 2K x 4K CCDs.
The one meter telescope, scheduled for operation in September 2000,
has a field of view of 3 square degrees (f/3) and will use a mosaic
of ten 2K x 4K CCDs.
Catalina Sky Survey (S. Larson):
The Catalina program consists of both a northern and southern
hemisphere search and follow up capability. In the north, the
Catalina Schmidt 0.7m (f/1.6) telescope is used for search while the
Mt. Lemmon 1.5 m (f/2.0) is used for follow up observations. In the
south, the Siding Spring Uppsala Schmidt 0.6 m (f/3) is currently
being used for search while the co-located 1.0 m (f/8) telescope is
used for follow up. Upgrades are in progress for the Catalina
Schmidt (corrector plate, new computers, dome control), the Uppsala
Schmidt (declination drive and control room), and Mt. Lemmon
(declination drive, computer controls, coma corrector). Proposed
upgrades include a thinned 4K x 4K chip for the Catalina Schmidt, a
0.9 m (f/1.7) optical system redesign for the Uppsala Schmidt and a
larger 4K x 4K chip for the Mt. Lemmon telescope.
LINEAR (G. Stokes):
While efforts to utilize the U.S. Air Force one meter aperture
Ground-based Electro-Optical Deep Space Surveillance (GEODSS)
telescopes for discovering NEAs go back several years, it was in
March 1998 that the LINEAR program began routine operations using a
special 1960 x 2560 CCD camera. This CCD is a thinned, back side
illuminated, frame transfer device that allows very fast readouts.
In October 1999, a second co-located GEODSS telescope was added to
the LINEAR survey and the combination of these two telescopes now
accounts for roughly 70% of all NEA discoveries.
LONEOS (E. Bowell):
The LONEOS 0.6 m Schmidt telescope (f/1.9) is currently making about
15,000 asteroid detections per lunation. With the recent
improvements in computer software (Sextractor) and the new camera
(two 2K x 4K thinned backside illuminated CCDs), the current
detection rate is about twice what it once was. Ted Bowell noted
that while an improvement to the current thermal environment might
increase the system efficiency somewhat, the current system has gone
about as far as it can so that plans are underway to investigate the
use of the USNO 1.5 m telescope in Flagstaff for future NEA searches.
NEAT (E. Helin):
NEAT began operations with the 1.0 m GEODSS telescope at Haleakala,
Maui, Hi in 1995. In 1999, NEAT was moved to the use of the MSSS 1.2
m telescope at the same location and began operations there in
February 2000. The current telescope not only has a larger aperture
but is available 18 nights per month whereas the GEODSS telescope was
only available about 6 nights/month. In addition, upgrades are
already in progress to convert the Palomar 1.2 m Schmidt telescope
into a NEA search instrument with operations expected to begin in
October 2000. The Maui MSSS 1.2 m telescope uses a 4Kx4K CCD with a
field of view of 2.6 sq. degrees whereas the Palomar Schmidt will
utilize an array of three 4Kx4K CCDs for a field of view of 3.9 sq.
degrees.
Spacewatch (R. McMillan)
The Spacewatch telescopes include the 0.9 m and the 1.8 m. When used
with the 4 x (4.6K x 2K) mosaic CCD, the 0.9 m has a field of view of
2.9 sq. degrees. When brought on line at the end of 2000, the 1.8 m
telescope will have a field of view of 0.32 sq. degrees and utilize a
2K x 2K CCD. The average rate of discovery of NEAs with H < 18.0 has
been about 7 per year since 1995. The Spacewatch telescopes are used
primarily for deep searches in limited areas for NEAs and Kuiper-belt
objects (KBOs) rather than the wide area NEA searches provided by the
other search programs. As a result, Spacewatch finds many of the
smaller NEAs, some KBOs and recently, the 17th satellite of Jupiter.
MPC (G. Williams)
Until Oct. 1998, most of the data processing of incoming observations
and orbit improvements were performed on one VAX workstation.
Starting in Oct. 1998, the first of the Alpha workstations were
brought on line for doing the orbit improvements while the VAX still
processed the observations. In early 1999, four clustered Alpha
workstations were brought on line to process the observations,
compute orbits and prepare the MPCs for export. The porting of the
entire MPC operations from the VAX to the Alpha systems has been very
time consuming and is still ongoing. Since late 1999, several
batches of MPCs have contained over 300,000 observations and the
expectation is that one of the 2000 MPC batches will break the
500,000 observation mark. Gareth noted a "follow up rating" that was
defined as the percentage of submitted observations made in a
specified period that can now be identified with previously known
objects or linked with other objects. For the first few months of
2000, these follow up ratings were about 95% for NEAT, 70% for
Spacewatch, 85% for LONEOS and 90% for Catalina and LINEAR.
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UK NEO TASK GROUP
At the International Astronomical Union meeting in Manchester UK,
David Williams gave a brief background on a report expected to be
released by the UK government in mid-September on their proposed
program for Near-Earth objects. No details were available at this
time, but we all look forward to this official government assessment
of the NEO risk and of ways that might be appropriate for the UK to
participate in the worldwide Spaceguard effort. Stay tuned.
================================================
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
