Subject: NSF Senate testimony today

From: David Morrison

Submitted: Wed, 7 Apr 2004 16:03:33 -0700

Message number: 200 (previous: 183, next: 204 up: Index)

Testimony on the NEO Hazard before the Senate Subcommittee on 
Science, Technology and Space, 7 April 2004

Dr. Wayne Van Citters
Division Director, Division of Astronomical Sciences, National 
Science Foundation

Thank you for the opportunity to present the position of the National 
Science Foundation on the important subject of Near Earth Objects. In 
responding to the questions that the Committee has presented to us, I 
will present a picture of NSF's support of research into the nature 
and origin of these objects, as well as potential important 
contributions that NSF-supported instrumentation and techniques could 
make to an expanded discovery and characterization effort.

  Background and Context

The Division of Astronomical Sciences supports basic research in 
astronomy covering a very wide range of subjects - from studies of 
objects in our own solar system to investigations of the beginning of 
the universe, including the very nature of matter and energy. In 
planning and conducting its programs, the Division benefits from the 
advice of the scientific community in many ways, including the 
recently established Astronomy and Astrophysics Advisory Committee 
(AAAC, jointly advising NSF, NASA, and DOE). The establishment of the 
AAAC recognizes the value of an integrated strategy to address 
national efforts to answer questions about our origins and our 
future. The number and nature of NEOs are clearly fundamental 
questions about both our origins and our future. In their March 15, 
2004 report the AAAC recommended a coordinated implementation effort 
to ensure timely development of the Large Synoptic Survey Telescope, 
calling it a key facility for the detection of potentially hazardous 
earth-intersecting objects as small as 300 meters.

Current Activity

A number of awardees in our Planetary Astronomy Program are 
investigating Near Earth Objects (NEOs). The proposals funded by our 
program are determined by the interest of the research community, as 
reflected in the number and subject matter of proposals that we 
receive, and the results of our merit review of these proposals. As 
one example, Dr. Derek Richardson at the University of Maryland will 
be modeling the tidal disruption of near Earth asteroids (NEAs) by 
the Earth's gravitational field to determine the frequency of binary 
NEA formation and the typical characteristics of the resulting binary 
asteroids. The results from this research will give insight into the 
internal structure of NEAs and may have implications for hazard 
mitigation strategies. In another effort, Richard Binzel at MIT will 
measure the near-infrared spectral properties of 40-60 NEOs per year. 
The observations will balance measurements that push the 
state-of-the-art limits of the technology for the smallest and 
faintest objects and measurements that provide sufficient detail for 
detailed mineralogical analysis. Research in this area also 
represents a substantial fraction of the use of the Arecibo planetary 
radar system, characterizing sizes, shapes, rotation rates, and 
configurations (single or binary, e.g.). The smallest system yet 
observed (a binary of 120m and ~40 m diameter components) was 
discovered in 2003. Measurements from a combination of Arecibo and 
NASA's Goldstone antenna from 1991 through 2003 demonstrated the 
existence of the Yarkovsky effect. This effect is an acceleration of 
the body related to the time delay between the absorption of solar 
radiation and the re-emission in the infrared. The observations 
clearly indicated that the acceleration must be included in orbit 
predictions. We have observed that the number of proposals to 
investigate NEOs has been increasing annually for the last few years. 
Of the proposals we receive on this topic, those that do best in our 
merit review competition are those proposing to characterize the 
physical properties of the objects. What are they made of? How were 
they formed and when? I believe NSF is currently playing the role for 
which it is best suited. It is funding individual investigators to 
further our understanding of the physical make-up of NEOs. The 
proposals for these investigations are subject to our normal merit 
review, thus insuring high quality basic research on these objects. 
In addition, it provides access to tools such as Arecibo that can 
enhance the discovery process.

  Looking to the Future

In recent years, there has been an increasing appreciation for the 
hazards posed by near-Earth objects, those asteroids and periodic 
comets (both active and inactive) whose motions can bring them into 
the Earth's neighborhood. In August of 2002, our colleagues at NASA 
chartered a Science Definition Team to study the feasibility of 
extending the search for near-Earth objects to smaller limiting 
diameters. The formation of the team was motivated by the good 
progress being made toward achieving the Spaceguard goal of 
discovering 90% of all NEOs with diameters greater than 1 km by the 
end of 2008. This raised the question of what, if anything, should be 
done with respect to the much more numerous smaller, but still 
potentially dangerous, objects. The team was tasked with providing 
recommendations to NASA as well as the answers to seven specific 
questions. We believe that the answers to these questions could form 
a solid basis for the direction of our research efforts and for more 
detailed studies of the best integrated strategy to carry on at the 
end of Spaceguard in 2008.

What are the smallest objects for which the search should be 
optimized? The Team recommends that the search system be constructed 
to produce a catalog that is 90% complete for potentially hazardous 
objects (PHOs) larger than 140 meters.

Should comets be included in any way in the survey? The Team's 
analysis indicates that the frequency with which long-period comets 
(of any size) closely approach the Earth is roughly one-hundredth the 
frequency with which asteroids closely approach the Earth and that 
the fraction of the total risk represented by comets is approximately 
1%. The relatively small risk fraction, combined with the difficulty 
of generating a catalog of comets, leads the Team to the conclusion 
that, at least for the next generation of NEO surveys, the limited 
resources available for near-Earth object searches would be better 
spent on finding and cataloging Earth-threatening, near-Earth 
asteroids and short-period comets. A NEO search system would 
naturally provide an advance warning of at least months for most 
threatening long-period comets.

What is technically possible? Current technology offers asteroid 
detection and cataloging capabilities several orders of magnitude 
better than the presently operating systems. This report outlines a 
variety of search system examples, spanning a factor of about 100 in 
search discovery rate, all of which are possible using current 
technology. Some of these systems, when operated over a period of 
7-20 years, would generate a catalog that is 90% complete for NEOs 
larger than 140 meters.

How would the expanded search be done? From a cost/benefit 
point-of-view, the report concludes that there are a number of 
attractive options for executing an expanded search that would vastly 
reduce the risk posed by potentially hazardous object impacts. The 
Team identified a series of specific ground-based, space-based and 
mixed ground- and space-based systems that could accomplish the next 
generation search. The choice of specific systems would depend on the 
time allowed for the search and the resources available.

What would it cost? For a search period no longer than 20 years, the 
Team identified several systems that they felt would eliminate, at 
varying rates, 90% of the risk for sub-kilometer NEOs, with costs 
they estimate to range between $236 million and $397 million for both 
ground and space components. They conclude that all of these systems 
have risk reduction benefits which greatly exceed the costs of system 
acquisition and operation.

How long would the search take? The Team concludes that a period of 
7-20 years is sufficient to generate a catalog 90% complete to 
140-meter diameter, which will eliminate 90% of the risk for 
sub-kilometer NEOs. The specific interval would depend on the choice 
of search technology and the investment allocated.

Is there a transition size above which one catalogs all the objects, 
and below which the design is simply to provide warning? The Team 
concluded that, given sufficient time and resources, a search system 
could be constructed to completely catalog hazardous objects with 
sizes down to the limit where air blasts would be expected (about 50 
meters in diameter). Below this limit, there is relatively little 
direct damage caused by the object. Over the 7-20 year interval 
(starting in 2008) during which the next generation search would be 
undertaken, the Team suggests that cataloging is the preferred 
approach down to approximately the 140-meter diameter level and that 
the search systems would naturally provide an impact warning of 
60-90% for objects as small as those capable of producing significant 
air blasts.

The path from where we are today to where we should be in 2014 is not 
defined in the conclusions of the study that NASA sponsored. Clear 
goals are defined; how one might reach them is wisely left to the 
scientific and technical community. At the national level, we must 
now examine these goals in detail, validate the conclusions, and 
determine how they might best be achieved.

NSF Plans for the Future

We are considering asking the AAAC to form a subcommittee to advise 
on the effort that would be appropriate beyond Spaceguard. Broadly 
based in the scientific and technical community, this subcommittee 
would consider the conclusions of recent studies, extract necessary 
research directions that would help us better understand the origin 
and nature of the objects known to date and help to chart the most 
productive course into the future. By the very nature of the charge 
to the AAAC, this would be an integrated look at the ground-based and 
space-based efforts that would make the most effective scientific 
advances in this area. Of particular interest to NSF would be the 
expansion of the individual investigator-driven basic research that 
we currently support, and a more detailed understanding of how such 
projects as the Large Synoptic Survey Telescope (LSST) and Panoramic 
Survey Telescope and Rapid Response System (Pan-STARRS) might best 
contribute to the discovery and characterization effort in the future.

The LSST is a proposed single 8.4meter aperture, very wide field 
telescope capable of surveying the entire sky visible from one 
hemisphere every two weeks. It has a variety of science drivers 
including the characterization of dark matter and dark energy, the 
discovery of many classes of transient objects such as supernovae and 
gamma-ray burst counterparts, and NEOs. Pan-STARRS, an Air Force 
funded project under construction in Hawaii, will be composed of 4 
individual telescopes of 1.8meter aperture observing the same region 
of sky simultaneously. In survey mode, i.e., searching for NEOs, 
Pan-STARRS will cover 6,000 square degrees per night. The whole 
available sky as seen from Hawaii will be observed 3 times during the 
dark time in each lunation. The LSST's ability to make fast, wide, 
and faint observations may make it uniquely suited to detecting small 
NEOs.

A model LSST survey covering 9,000 square degrees of sky along the 
ecliptic, three or four times a month, to a limiting V magnitude of 
24.0, achieved a ten-year completeness of about 90% for NEOs larger 
than 250 m, and about 80% for NEOs down to 140 m as called for by the 
NASA study. The requirements placed on the telescope, telescope 
operations, data system and detectors by the NEO detection challenge 
are considerable. By reaching objects 100 times fainter than those 
currently observed in the NEO surveys, Pan-STARRS is being designed 
to help complete the Congressional mandate to find and determine 
orbits for the 1-km (and larger) threatening NEOs. Further, it should 
push the detection limit for a complete (99%) sample down to objects 
as small as 300-meters in diameter.

Design studies over the next several years will be needed to 
determine the strategy for attacking the NEO problem and whether it 
is best carried out with a single telescope like the LSST or whether 
an array of smaller telescopes such as Pan-STARRS is more appropriate 
for this particular problem. NSF's Division of Astronomical Sciences 
has begun planning for such studies and we have been actively joined 
by our colleagues at NASA, who will contribute their knowledge and 
experience in the handling of large data bases and archives.

Conclusion

In conclusion, Mr. Chairman, NSF is already pursuing a significant 
amount of basic research in this important area. We are guided, as 
always, by the scientific community through our merit review process. 
We are laying plans for new facilities and expanded research activity 
that speak to many basic questions about the nature and origin of 
these objects, and are confident that the body of knowledge so gained 
will have important application to any eventual risk-mitigation 
effort.

-- 
+++++++++++++++++++++++++++++++++++++++++++

David Morrison, NASA Ames Research Center 240-1
Tel 650 604 5094; Fax 650 604 4251
david.morrison@nasa.gov or dmorrison@arc.nasa.gov
website: http://astrobiology.arc.nasa.gov
website: http://nai.arc.nasa.gov
website: http://impact.arc.nasa.gov

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