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This Committee has been a leader in focusing
attention on the importance of cataloging and characterizing
Earth-approaching asteroids and comets. In 1992, the Committee
on Science directed that NASA sponsor two workshop studies,
the NEO Detection Workshop, which was chaired by NASA, and
the NEO Interception Workshop, which was chaired by the Department
of Energy. In March 1993, the Science Committee held a hearing
to review the results of these two workshops. In 1995, at
the Committee’s request, NASA conducted a follow-up study
which was chaired by the late Dr. Gene Shoemaker. Each of
these studies stressed the importance of characterizing and
cataloging NEOs with diameters larger than 1 km within the
next decade. We have taken steps to put us on a path to achieving
this goal. I am here today to tell you about those steps,
as well as to bring you up to date on the rich program of
space missions to NEOs and related objects.
The NEO population is derived from a variety
of scientifically interesting sources including planetesimal
fragments and some Kuiper belt objects. Indeed, the Office
of Space Science Strategic Plan includes as a specific goal
“ ...to complete the inventory and characterize a sample
of Near Earth Objects down to 1 km diameter.” While the
threat of a catastrophic collision is statistically small,
NASA has a vigorous program of exploration of NEOs planned,
including both asteroids and comets.
There has been much recent discussion about
the potential threat posed by NEOs, but NASA has long been
interested in them from a scientific standpoint. NEO investigations
have had to compete for support against a number of other
compelling science programs; funding selection criteria were
based principally on scientific merit. This approach has led
to the detection of over 400 NEOs, including more than 100
objects larger than 1 km, and to a rapid advancement of the
technologies necessary for NEO detection. In fact, this research
effort has demonstrated that we can inventory the NEO population
in a reasonable time, about a decade, with an achievable increase
in funding from recent levels.
A little less than a year ago, NASA initiated
a study of its existing NEO research to determine how well
we were doing in terms of reaching our goal of inventorying
the population of NEOs larger than 1 km and characterizing
a sample of them. While we have made some impressive strides,
it became apparent that the funding levels resulting from
scientific competitive review ($1-1.5 M per year) was not
sufficient to accomplish our goal. The detection of new NEOs
in 1997, the last year for which we have statistics, is barely
10% of the rate needed to achieve the goal suggested in the
Shoemaker report (detection of 90% of the NEO population larger
than 1 km within a decade). In simple terms, we need to survey
about 20,000 square degrees of sky a month for NEOs to a limiting
brightness of approximately 20th magnitude to accomplish the
inventory. To understand what this means, note that 20,000
square degrees is about half the sky and that magnitudes are
a measure of apparent brightness-a 6th magnitude object is
at the limit of detection for the human eye and 20th magnitude
is almost 100,000 times fainter.
I would now like to describe briefly the existing
search programs, NASA’s plans to improve them, and some
promising new research programs which we are considering.
I will also comment on our joint activities with the Air Force
Space Command. All of these efforts are directed toward increasing
the rate of discovery of NEOs in order to reach our goal.
NASA’s ground-based NEO program comprises
three parts: Spacewatch, the Near-Earth Asteroid Tracking
(NEAT) program, and the Lowell Near Earth Asteroid Survey
(LONEOS).
Spacewatch is a program at the University of
Arizona, led by Dr. Tom Gehrels, which has done much of the
pioneering work in the field of NEO detection. This group
is responsible for more NEO discoveries than any other. The
current Spacewatch Program searches 200 square degrees of
sky per month to a depth of 21st magnitude. This year NASA
is funding a new state-of-the-art focal plane camera for Spacewatch,
which will lead to an 8-fold increase in the area of sky that
they search each month (to 1600 square degrees per month).
We hope in the future to assist them in their efforts to bring
their new 1.8 m telescope on line. This telescope will enable
them to detect even fainter NEOs.
NEAT is a program headed by Dr. Eleanor Helin
at the Jet Propulsion Laboratory. NEAT uses a specialized
camera, which is based on a 4096x4096 CCD array for use on
the 1 m GEODSS (Ground-based Electro-Optical Deep Space Surveillance)
telescope, operated by United States Air Force Space Command
(USAFSC) on Haleakala, Maui, Hawaii. This group is currently
limited by the number of nights per month on which they can
observe the sky using the GEODSS system. They are presently
observing six nights per month on one of the seven GEODSS
telescopes. With recent improvements they are now able to
search 800 square degrees per night (4800 square degrees per
month) to about 20th magnitude. We have funded the construction
of 2 more cameras, which we hope to install on two other GEODSS
telescopes. This increase in the level of effort for NEO detection
is being discussed in the NASA-USAFSC Partnership Council
co-chaired by NASA Administrator Daniel Goldin and AFSC Commander
Gen. Howell Estes. It is in principle possible to scan 21,000
square degrees a month with three cameras and full access
to three of the GEODSS telescopes. It is important to note
that the GEODSS system includes one southern hemisphere site.
While we certainly hope to increase our surveying
ability using the GEODSS system, we are aware that it has
other vital missions. NASA#146;s FY 1999 budget request includes
sufficient funding for the construction of four more NEAT
cameras, which will enable us to equip all seven GEODSS telescopes.
The final application of the funds will depend on the demonstration
that the NEAT camera can support the existing mission of the
GEODSS system as well as the search for NEOs. This matter
is currently being reviewed by the Partnership Council on
NEOs.
LONEOS is led by Dr. Ted Bowell at Lowell Observatory
in Flagstaff, Arizona. This group has great potential (capability
to observe 4,300 square degrees a month down to 20th magnitude);
however, they have not yet reached this level of performance.
We are funding an augmentation to buy a second focal plane
CCD and to support additional software development in order
to allow them to reach their performance objective.
The increased interest in the search for NEOs
has led to several recent proposals from new groups:
We are supporting a new search program at the
University of Arizona, which is headed by Mr. Steven Larson,
to refurbish an existing telescope on Mount Lemon. When fully
operational, this system will survey 8,000 square degrees
of sky per month to a depth of 19th magnitude. This program
will be fully operational within a year.
NASA is evaluating a proposal for support of
a very promising search program from the MIT Lincoln Labs.
This effort called LINEAR (Lincoln Near Earth Asteroid Research
program) uses a state-of-the-art camera which was developed
as a possible prototype for the next generation GEODSS detector.
They are proposing to use a 1 m telescope at their Experimental
Test Site near Socorro, New Mexico, to survey 10,000 square
degrees down to 21st magnitude each month.
With coordination of these different observational
programs, NASA believes it is possible to obtain the level
of sky coverage to the appropriate limiting magnitude required
to complete the survey. NASA has already committed over $3M
this year, much of it to fund improvements to focal plane
detectors, software, and electronics. NASA is committed to
funding both existing and new search programs at, at least,
the FY 1998 level. We believe this is close to the level required
to achieve our objective.
The study of the physical characteristics of
NEOs is a major focus of both ground-based research and space
missions. The ground-based work includes NASA-supported radar
imaging of NEOs utilizing the Arecibo Radio Telescope and
spectroscopy of NEOs from optical/IR telescopes to determine
their composition.
Several NASA missions will travel to asteroids
and/or comets to provide us with exciting new scientific insights
about these objects; at the same time this information is
valuable for any future effort to respond to an impact threat.
Over the next decade NASA will invest approximately $1B in
these missions. Missions in flight or in development are:
, which will
reach the near-Earth object Eros in January, 1999, orbit for
one year to measure its surface and interior properties, and
then land on Eros.
, which
will fly by a set of three short-period comets and make the
first detailed comparative study of cometary nuclei.
, which
will return a sample from the coma of short-period comet in
2006.
, is a European
Space Agency (ESA) mission to comet P/Wirtanen. NASA is providing
three ROSETTA orbiter instruments and support to eight U.S.
co-investigators on other orbiter instruments.
Missions soon to enter development are:
with
Japan to deploy a US-provided micro-rover on the surface of
an NEO and to return a sample of the asteroid to Earth in
2006.
to land on a comet, measure its composition, test sampling
and sample-return technologies for small bodies, and perhaps
even return a sample.
to survey one or more Kuiper belt objects before deflection
into the inner solar system.
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.
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