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RADAR INVESTIGATION OF NEAR-EARTH ASTEROIDS Steve Ostro JPL/Caltech http://echo.jpl.nasa.gov

RADAR INVESTIGATION OF NEAR-EARTH ASTEROIDS Steve Ostro JPL/Caltech http://echo.jpl.nasa.gov Frontiers of Astronomy with the
World's Largest Radio Telescope Sep. 13, 2007 Washington, DC. NEA Radar Investigations Since 1997. Red = Arecibo Green = Goldstone Blue = G,A Purple = A,G.

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RADAR INVESTIGATION OF NEAR-EARTH ASTEROIDS Steve Ostro JPL/Caltech http://echo.jpl.nasa.gov

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  1. RADAR INVESTIGATION OF NEAR-EARTH ASTEROIDSSteve OstroJPL/Caltechhttp://echo.jpl.nasa.gov Frontiers of Astronomy with the
World's Largest Radio TelescopeSep. 13, 2007Washington, DC

  2. NEA Radar Investigations Since 1997 Red = AreciboGreen = Goldstone Blue = G,APurple = A,G

  3. Radar Measurement Precision Range Radial Velocity (meters) (meters/second) Best radar resolution <10 ~0.0001 Asteroid “size” 1000 ~0.01 to 1 Asteroid “location” 10,000,000,000 10,000

  4. Radar Images of 1620 Geographos

  5. Radar Images and 3D Model of 4179 Toutatis

  6. 25143 Itokawa radar model Hayabusa Spacecraft approach image

  7. Radar Images 3D Models 4 km

  8. Itokawa Eros

  9. Contact Binaries Disruption of kilometre-sized asteroids by energetic collisions. Asphaug et al. (1998), Nature393, 437-440. Near-Earth Asteroid 2005 CR37: Radar Images of a Candidate Contact Binary. L. Benner et al. (2006), Icarus182, 474-481. 11066 Sigurd 2002 HK12 2002 NY40 4486 Mithra 3908 Nyx

  10. Non-Principal-Axis Rotators: Toutatis 1999 JM8 Mithra

  11. Orbits About 4769 Castalia Castalia-fixed frame Inertial frame Scheeres et al. (1996), Icarus 121,67-87

  12. Toutatis Return Orbits 1.2 days 2.9 days 168 days Toutatis-fixed frame Inertial frame Scheeres et al. (1998), Icarus132, 53-79.

  13. Arecibo Radar Imaging of (66391) 1999 KW4

  14. Direct Detection of the Yarkovsky Effect by Radar Ranging to Asteroid 6489 Golevka S. R. Chesley, S. J. Ostro, D. Vokrouhlicky, D. Capek, J. D. Giorgini, M. C. Nolan, J. L. Margot, A. A. Hine, L. A. M. Benner, and A. B. Chamberlin. Science 302, 1739-1742 (2003).

  15. Densities of Potentially Hazardous Asteroids Itokawa 1.9 ± 0.13 g/cm3 7% Hayabusa rendezvous KW4 Alpha 1.97 ± 0.24 12% binary; radar imaging KW4 Beta 2.81 (+0.82, −0.63) 39% binary; radar imaging Golevka 2.7 Arecibo ranging and Goldstone imaging 2002 CE26 Alpha 0.9 (+0.5, -0.4) 50% binary; Arecibo imaging 2000 DP107 Alpha 1.7

  16. SUMMARY Radar is our most powerful astronomical source of information about NEA physical properties.Radar is identifying: objects that must be metallic and objects that must be stony featureless spheroids and shapes that are elongated and irregular monolithic pieces of rock and unconsolidated rubble piles small-scale morphology ranging from smoother than the lunar surface to rougher than the rockiest terrain on Earth or Mars  objects with geologically interesting features (craters, blocks, and linear structures) rotation periods ranging from minutes to weeks  non-principal-axis spin states contact binaries binary systemsArecibo is 20X more powerful than anyother existing or planned radar.Arecibo’s exploration of the NEA Frontier has barely begun.

  17. RADAR INVESTIGATION OF NEAR-EARTH ASTEROIDSSteve OstroJPL/Caltechhttp://echo.jpl.nasa.gov Frontiers of Astronomy with the
World's Largest Radio TelescopeSep. 13, 2007Washington, DC

  18. backup slides

  19. The Key to Understanding the KW4 System:Simulations that take the model shapes, masses, and average rotations and orbit as initial conditions for integrations using the actual gravitational potentials produced by the shapes and the coupling between the components’ motions:Scheeres et al. 2006, Fahnestock and Scheeres 2007.

  20. Significance of the KW4 Investigation- best images yet of a binary small body - best physical characterization of a km+ PHA - most unusual NEA yet observed + novel physical phenomena * Alpha shape * Alpha high porosity ==> rubble pile * Alpha equatorial ridge almost in orbit * Alpha spinning near disruption limit * Beta libration, oscillations in orbit size and shape * coupling of orbital and rotational dynamics is critical * excited: Role of Sun and probably Earth flybys in excitation * young - whole new realm of (extremely complex) dynamics - major implications for dealing with the collision hazard - milestone in understanding exotic processes and properties of NEAs - KW4, as unusual as it appears, may be similar to many binary NEAs. - major lines of inquiry opened up: three-body problem modeling system’s formation understanding dissipation and rigidity in low-g particulate media

  21. Radar reveals extreme diversity in NEAs’ surface bulk density and roughness

  22. NEA surface roughness depends on compositional class

  23. Dimensions: 1.53 x 1.50 x 1.35 km + 3% 0.57 x 0.46 x 0.35 km + 6% Density: 1.97 + 0.24 g cm-3 2.81 (+0.82 -0.63) g cm-3 Resembles Itokawa (1.95 + 0.14 ) Eros (2.77 + 0.03) Ida (2.6 + 0.5) Porosity: 40% to 66%, 29% to 58% Pole obliquity: 3.2º (+4.3º, -3.2º) 3.2º assumed (from orbit sol’n) Rotation period: 2.7645 + 0.0003 h 17.4223 h assumed (from orbit sol’n); Beta’s average rotation is synchronous with the long axis pointed toward Alpha, but librates around that orientation. Alpha Beta

  24. (66391) 1999 KW4 Radar Imaging Data Set

  25. data fit model data fit model image image image image

  26. Gravitational Slopes on 6489 Golevka 600 meters

  27. Geometry of Delay-Doppler Radar Images Range Doppler Frequency 3D Model Radar Image

  28. http://echo.jpl.nasa.gov/~ostro/kw4

  29. Alpha’s equator has minimum potential energy,widely varying effective gravitational slopes, and nearly vanishing total acceleration.

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