Defending Planet Earth Near-Earth-Object Surveys and Hazard Mitigation Strategies (2010) / Chapter Skim
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3 Survey and Detection of Near-Earth Objects
3 Survey and Detection of Near-Earth Objects
Pages 29-50
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From page 29... ...
The criteria for the assessment of the success of an NEO detection mandate rely heavily on estimates that could be in error, such as the size of the NEO population and the average reflectivity properties of an object's surface. For many years, the average albedo (fraction of incident visible light reflected from an object's surface)
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From page 30... ...
Searching should continue to identify as many of the remaining objects and objects newly injected into the NEO population as possible, especially imminent impactors. THE SPACEGUARD EFFORT Recognizing that impacts from near-Earth objects represent a hazard to humanity, the United States, the European Union, Japan, and other countries cooperatively organized to identify, track, and study NEOs in an effort termed "Spaceguard." From this organization, a nonprofit group named the Spaceguard Foundation was created to coordinate NEO detection and studies; it is currently located at the European Space Agency's ( ESA's)
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From page 31... ...
The MPC is currently able to handle the large volumes of data expected in the near future from NEO discovery programs using larger telescopes. Near Earth Object Program Office The Near Earth Object Program Office operates at the Jet Propulsion Laboratory (JPL)
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From page 32... ...
NEAT ceased operations in 2007 after detecting over approximately 20,000 objects, about 430 of which were NEOs. PRESENT NEAR-EARTH-OBJECT DISCOVERY EFFORTS In 2005, five NEO detection programs were operational: Catalina Sky Survey (CSS)
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From page 33... ...
Thus, the detections of potentially hazardous NEOs by an infrared telescope (one sensitive to infrared light) will result in a more accurate size-frequency distribution for these objects.
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From page 34... ...
AsteroidFinder will thus aid in the assessment of the impact hazard due to NEOs. ADDRESSING THE 140-METER REQUIREMENT: FUTURE GROUND- AND SPACE-BASED NEAR-EARTH-OBJECT DISCOVERY EFFORTS The NASA Authorization Act of 2005 ordered NASA to "plan, develop, and implement a Near-Earth Object Survey program to detect, track, catalogue, and characterize the physical characteristics of near-Earth objects equal to or greater than 140 meters in diameter in order to assess the threat of such near-Earth objects to Earth.
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From page 35... ...
To detect 90 percent of all potentially hazardous NEOs larger than 140 meters in diameter, a telescope must be able to reach a limiting magnitude of M = 24. With the magnitude limitations discussed above, CSS, LINEAR, and Spacewatch are incapable of meeting the goal of discovering 90 percent of all potentially hazardous NEOs larger than 140 meters in diameter or greater by 2020 or any later date.
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From page 36... ...
show that by opti mizing operations for NEO detection, the required time could be reduced to about 12 years to detect 90 percent of all potentially hazardous NEOs larger than 140 meters in diameter (Chesley, 2008)
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From page 37... ...
PanSTARRS 4, even if completed and used on an "optimistic" schedule, could not alone meet the 2020 dead line, or any date, for detecting 90 percent of all potentially hazardous NEOs larger than 140 meters in diameter. Catalina Sky Survey Binocular Telescopes The CSS University of Arizona's team of astronomers proposes a series of three binocular telescopes fully dedicated to discovering NEOs (Beshore, 2009)
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From page 38... ...
Each binocular telescope could survey independently; images obtained simultaneously from any combination of these telescopes could be added together. Three binocular telescopes operated together would produce an equivalent mirror diameter of 4.2 meters and could detect objects to a limiting diameter of R = 23.2 (Beshore, 2009)
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From page 39... ...
The CSS+ would have capability unique among the proposed NEO survey telescopes to acquire spectra of the sunlight reflected from a target NEO across the broad wavelength range of 0.4 to 2.4 microns. Small mirrors would be installed in the instrument attached to a binocular telescope that could switch between the instrument's imaging mode to a pair of low-resolution spectrographs.
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From page 40... ...
However, CSS+ could not alone detect 90 percent of all potentially hazardous NEOs larger than 140 meters in diameter, as its limiting magnitude is not sufficient to reach the faintest NEOs. Discovery Channel Telescope The 4.2-meter-diameter mirror Discovery Channel Telescope (DCT)
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From page 41... ...
; • Space-based searches can be conducted above Earth's atmosphere, eliminating the need to calibrate the effects introduced by the atmosphere on the light from an NEO; and • Observations can be made 24 hours a day. Two concepts for space-based infrared telescopes are discussed here, as illustrations of means to satisfy the congressional mandate to identify 90 percent of all potentially hazardous NEOs larger than 140 meters in diameter.
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From page 42... ...
The NEO Survey design allows observations over slightly more than the entire anti-Sun hemisphere. It should complete its mission of detecting more than 90 percent of all potentially hazardous NEOs larger than 140 meters in slightly under 8 years.
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From page 43... ...
. The sixth column describes programmatic risks, if any; it also encapsulates the risk that projects whose primary purpose is not the search for NEOs might not, in fact, carry out the NEO survey over the lifetime of the project.
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From page 44... ...
None already exists 0.5-m IR at L1/L2 11 88 5 6-10 µm, Not funded; primary 2% launch losse IR light curve purpose is NEO discovery and study 2-m visible at 16 83 6 VR Not funded; primary 2% launch losse L1/L2 visible light purpose is NEO curve discovery and study 0.5-m IR at Venus 7.5 95 5 6-10 µm, Not funded; primary 2% launch losse IR light curve purpose is NEO discovery and study 2-m visible at 7 94 5 VR Not funded; primary 2% launch losse Venus visible light purpose is NEO curve discovery and study 0.5-m IR at Venus; 7.5 ~95 5 3-5.5, 6-10 µm, Not funded; primary 2% launch losse –2 bandpass IR light curve purpose is NEO discovery and study 5f Combined systems: 5.5 97 gri, 6-10 µm Requires ground and 2% launch losse 0.5-m IR at Venus light curves in space facilities to be + PS1 visible and IR funded and operated 7g Combined systems: 3-4 98 ugriZY, 6-10 µm Requires ground and 2% launch losse 0.5-m IR at Venus light curves in space facilities to be + LSST visible and IR funded and operated
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From page 45... ...
allows a detection of 90 percent of the potentially hazardous NEOs down to 50-meter-diameter NEOs but is still not adequate to detect 90 percent of those down to 30 meters in diameter in 30 years of operation. Detecting 90 percent of the smallest NEOs that might cause significant damage on impact is thus a very difficult task.
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From page 46... ...
NOTE: LSST, Large Synoptic Survey Telescope; PanSTARRS, Panoramic Survey Telescope and Rapid Response System. SOURCE: Courtesy of Steve Chesley, Jet Propulsion Laboratory.
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From page 47... ...
SOURCE: Courtesysof Steve Chesley, Jet Propulsion Laboratory. Figure 3.8.ep 1.0 0.9 0.8 0.7 Fraction Completed 0.6 140 m 50 m 0.5 30 m 0.4 0.3 0.2 0.1 0.0 0 5 10 15 20 25 30 Years from Star t of Operations FIGURE 3.9 Years to completion for a shared Large Synoptic Survey Telescope (LSST)
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From page 48... ...
For different size regimes, some overarching conclusions can be drawn: • Ninety percent completeness for the detection of potentially hazardous NEOs 0 meters in diameter or largerIn theory, this goal could be achieved by 2020. Experience suggests, however, that the congressional goal cannot be met by 2020.
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From page 49... ...
Imminent Impactors: NEOs on Final Approach to an Earth Impact With the discovery of NEO 2008 TC3, found within 19 hours of impact into the Sudan desert, the committee discussed the question of an increasing capability to detect imminent impactors on their final approach to Earth. Optimizing the detection of imminent impactors requires a different observing strategy than the approaches dis cussed above designed to discover hazardous NEOs with long lead times before impact.
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From page 50... ...
Presentation to the Survey/Detection Panel of the Committee to Review Near-Earth Object Surveys and Hazard Mitigation Strategies, April 20-22, Tucson, Arizona. Spahr, T., Minor Planets Center, Harvard-Smithsonian Center for Astrophysics.
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