TECH INNOVATERS

project is not completed its only vertually validated

project is not completed its only vertually validated

Efforts to find and catalog asteroids over the past 200 years were initially inspired by scientific curiosity and a desire to understand the structure of the solar system. More recently these efforts have been spurred by the NASA search goal and as part of the International Spaceguard effort. The NASA goal, mandated by the US Congress, is to discover 90% of all potential impactors with diameters in excess of 1 km by the year 2008 (NASA, 1998). One-kilometer-diameter asteroids are thought to mark the threshold size for globally catastrophic consequences in a collision, and various models indicate there are between 500 and 2100 such objects (Morrison et al., 1992; Rabinowitz et al., 2000; Bottke et al., 2000; Stuart, 2000). The ability to achieve the NASA goal with existing and proposed systems can be viewed as a function of the search volume for these systems with respect to the size of the target object. Search volume is defined as the maximum range at which a system can detect an object of a certain diameter multiplied by the area of sky covered. As the diameter of the limiting object decreases, so does the maximum range at which it can be detected, and the search volume therefore decreases. Longer integration times may increase the limiting range but will decrease the area of sky covered due to limited time available for searching, thereby not necessarily increasing the volume. Improved detector and computing technology has stretched the search volume for 1-km objects to make the NASA goal potentially achievable in the future with the current smaller aperture telescopes, and discussion is shifting toward extending the inventory to smaller objects that could cause significant regional damage. For example, a catalog 90% complete to the 300-m size is one of the proposed objectives of the Large-aperture Synoptic Survey Telescope (NRC, 2001) recommended by the recent astronomy decadal study. The Spaceguard report (Morrison et al., 1992) estimates that there are between 12,500 and 50,000 NEAs larger than 300 m. Below a few hundred meters in size, the limited search volume of existing or proposed search systems precludes near-term cataloging. Such objects will require a continuous search effort that could also address detection of potentially dangerous long-period comets not amenable to cataloging. Below ~100 m, the mass that survives entry through the atmosphere is likely too small to create widespread destruction. Despite 200 years of searching for asteroids and the dramatic increase in discoveries and observations in the past decade, we are just now approaching the point of having found approximately one-half of the large NEAs set as the goal by NASA. This state of affairs testifies to the inherent challenges associated with finding asteroids in general and NEAs in particular. Searching for asteroids has all the typical difficulties associated with finding faint objects in a cluttered and complex environment. Specifically, the faint observed magnitudes limit the search volume; search areas and times are denied by the Sun, Moon, and weather; and the cluttered stellar background makes detection difficult, especially in the galactic plane

ous search strategies is the NEO sky density as a function of detection limit. This plot shows heuristically that at the simplest level the probability of detecting NEAs actually increases away from opposition due to the longer line of sight through higher-density regions of NEOs. The negative aspects of such a search include observing through greater air mass and less favorable solar phase angles. Each of these effects should be considered, and each varies system to system with the location and sensitivity of equipment. A rigorous discussion of probabilities of detection is covered by Jedicke (1996) and supports a similar conclusion regarding the potential benefits of searching away from opposition: The probability of detection increases away from opposition if you can search deep enough. Searching away from the ecliptic generally does not provide for optimal detection efficiency. For any given asteroid, it is generally easier to detect it near the ecliptic. However, NEAs on an inclined orbit are less likely to be found at small ecliptic latitudes because they reside longer at high apparent latitudes. This may justify an all-sky search strategy. In 1998, three large search programs began operation: LINEAR, Catalina Sky Survey, and LONEOS. Due to the significantly increased search capability with the introduction of these surveys, full-sky searches have become more common, primarily through these three programs. The effect has been to refine our understanding of the statistical distribution of the known population. Figure 4a shows the distribution by inclination of all known NEAs with H ≤ 18.0 discovered by LINEAR, LONEOS, and Catalina Sky Survey as compared to those discovered by other surveys more likely to be concentrating near ecliptic opposition. Note that the distribution is both flatter and has a longer tail towards higher inclinations for discoveries by these three. Figures 4b and 4c show similar plots for eccentricity and semimajor axis, with some differences amongst

Maximizing survey coverage precludes making followup observations of potential NEOs that are more efficiently made with smaller field telescopes. Confirming observations on subsequent nights provide the extended arc needed to determine their orbits with sufficient precision to identify NEOs. Fortunately, there is a sizable network of amateur and professional observers who consult the Minor Planet Center’s NEO Confirmation Web page each night and provide the bulk of additional astrometry needed to identify NEOs. In the past few years, the development of affordable CCD cameras, fast computers, sophisticated software, better reference star catalogs, larger telescopes, and the ability to communicate effectively over the Internet has enabled amateurs and professionals at small observatories to out-produce the professionals at major observatories of 10–15 years ago. Amateur followups have become a vital component in the NEO inventory effort down to V ~ 20. In addition to providing the necessary astrometry, this followup contribution is expanding toward obtaining better time-resolved photometry from which sizes and shapes of NEOs can be estimated.

Bottke W. F. Jr., Jedicke R., Morbidelli A., Petit J. M., and Gladman B. (2000) Understanding the distribution of near-Earth asteroids. Science, 288, 2190–2194. Bowell E. and Muinonen K. (1994) Earth-crossing asteroids and comets: Groundbased search strategies. In Hazards Due to Comets and Astroids (T. Gehrels, ed.), pp. 149–197. Univ. of Arizona, Tucson. Carusi A., Gehrels T., Helin E. F., Marsden B. G., Russell K. S., Shoemaker C. S., Shoemaker E. M., and Steel D. I. (1994) Near-Earth objects: Present search programs. In Hazards Due to Comets and Astroids (T. Gehrels, ed.), pp. 127–147. Univ. of Arizona, Tucson. Gehrels T. (1986) CCD scanning. In Asteroids, Comets, and Meteors II (C.-I. Lagerkvist et al., eds.), pp. 19–20. Uppsala Univ., Uppsala. Gehrels T. (1991) Scanning and charge-coupled devices. Space Sci. Rev., 58, 347–375. Harris A. W. (1998) Evaluation of ground-based optical surveys for near-Earth asteroids. Planet. Space Sci., 46, 283–290. Isobe S., Mulherin J., Way S., Downey E., Nishimura K., Doi I., and Saotome M. (2000) A cost-effective, advanced-technology telescope system for detecting near-Earth objects and space debris. In Proceedings of SPIE on Telescope Structures, Enclosures, Controls, Assembly/Integration/ Validation and Commissioning, Vol. 4004. Jedicke R. (1996) Detection of near-Earth asteroids based upon their rates of motion. Astron. J., 111, 970–982. Larson S., Spahr T., Brownlee J., Hergenrother C., and McNaught R. (1999) The Catalina sky survey and southern hemisphere NEO survey. In Proceedings of the 1999 AMOS Technical Conference, pp. 182–186. Marsden B. G. (1994) Asteroid and comet surveys. In Astronomy from Wide-Field Imaging (H. T. Mac Gillivray et al., eds.), pp. 385–399. Kluwer, Dordrecht. Minor Planet Center (2001) Sky Coverage Services for Observers. (Available on line at http://scully.harvard.edu/~cgi/SkyCoverage. html.) Morrison D. and 23 colleagues (1992) The Spaceguard Survey: Report of the NASA International Near-Earth-Object Detection Workshop. Jet Propulsion Laboratory, Pasadena. NASA (1998) Strategic Plan of NASA’s Office of Space Science 1998. U.S. Govt. Printing Office, Washington, DC. NRC (National Research Council) Astronomy and Astrophysics Survey Committee (2001) Astronomy and Astrophysics in the New Millennium. National Academy Press, Washington, DC. 246 pp. Pravdo S. H., Rabinowitz D. L., Helin E. F., Lawrence K. J., Bambery R. J., Clark, Groom S. L., Levin S., Lorre J., Shaklan S. B., Kervin P., Africano J. A., Sydney P., and Soohoo V. (1999) The Near-Earth Tracking (NEAT) program: An automated system for telescope control, wide-field imaging, and object detection. Astron. J., 117, 1616–1633 Rabinowitz D. L., Helin E. F., Lawrence K., and Pravdo S. (2000) A reduced estimate of the number of kilometre-sized near-Earth asteroids. Nature, 43, 165–166. Rabinowitz D. L. (1992) The flux of small asteroids near the Earth. In Comets, Asteroids, Meteors 1991 (A. W. Harris and E. Bowell, eds.), pp. 481–485. NASA, Washington, DC. Stokes G. H., Evans J. B., Viggh E. M., Shelly F. C., and Pearce E. C. (2000) Lincoln Near-Earth Asteroid Program (LINEAR). Icarus, 148, 21–28. Stuart J. S. (2000) The near-Earth asteroid population from Lincoln near-Earth asteroid research (LINEAR) data (abstract). Bull. Am. Astron. Soc., 32, 1023. Viggh H. E. M., Stokes G. H., Shelly F. C., Blythe M. S., and Stuart J. S. (1998) Applying Electro-optical space surveillance technology to asteroid search and detection: The LINEAR program results. Proceedings of the Sixth International Conference and Exposition on Engineering, Construction, and Operations in Space, p

#hardware #problemsolved

This project has been submitted for consideration during the Judging process.