Asteroid 5261Eureka (Mars Trojan) Frames taken 10 minutes apart, tracking asteroid motion

1. Asteroid 5261Eureka (Mars Trojan) Frames taken 10 minutes apart, tracking asteroid motion

4. Discovery of Asteroids • Asteroid 1 Ceres discovered 1801 January 1 by Giuseppe Piazzi in Palermo, Sicily, and observed for 40 nights.

5. Discovery of Asteroids • Asteroid 1 Ceres discovered 1801 January 1 by Giuseppe Piazzi in Palermo, Sicily, and observed for 40 nights. • Carl Friedrich Gauss invents “Gauss’ Method” of orbit determination to allow recovery in 1802.

6. Discovery of Asteroids • Asteroid 1 Ceres discovered 1801 January 1 by Giuseppe Piazzi in Palermo, Sicily, and observed for 40 nights. • Carl Friedrich Gauss invents “Gauss’ Method” of orbit determination to allow recovery in 1802. • Three more asteroids discovered over the next few years, no more until 1847.

7. Discovery of Asteroids • 3000 numbered by 1985. • 20957 numbered as of 2000 Jan 19. • 26073 numbered as of 2001 June 7 • 43721 numbered as of 2002 June 24. • 65634 numbered as of 2003 June 19. • 85117 numbered as of 2004 June 14 • 99947 numbered as of June 2005, then a 5 month hiatus. • 129437 numbered as of 2006 June 19 • 189005 numbered as of 2008 June 20 • 241562 numbered as of 2010 May 27 • 279722 numbered as of 2011 May 17

8. Near-Earth Asteroid Discoveries

9. Why Study Asteroids? • Solar System Formation • Many asteroids are believed to be relatively unprocessed remnants of Solar-System formation.

10. Why Study Asteroids? • Solar System Formation • Many asteroids are believed to be relatively unprocessed remnants of Solar-System formation. • Space Resources • Substantial colonization of space requires bulk materials that are too expensive to haul from Earth. Near-Earth asteroids can provide a very low delta-V source of materials.

11. Meteorites Los Angeles Shergottite (Martian Meteorite) Meteorites provide samples of extraterrestrial bodies, but where did they come from? Korra Korrabes H3 Chondrite Origin Unknown

12. Bilanga Meteorite 5 mm across

13. Why Study Asteroids? • Solar System Formation • Many asteroids are believed to be relatively unprocessed remnants of Solar-System formation • Space Resources • Substantial colonization of space requires bulk materials that are too expensive to haul from Earth. Near-Earth asteroids can provide a very low delta-V source of materials. • Impact Hazard

14. Impact Hazard Fig. 8-28, p. 179

15. Where are the Asteroids?

18. When Worlds Collide Meteorites are fragments of asteroids created in a collision

19. Collisional Evolution

20. Asteroids and Meteorites • Meteorites can be studied in great detail. • Almost all of our understanding of Solar System formation and evolution comes from analysis of meteorites. • We typically have little information as to their parent bodies. • What do we learn from the asteroids themselves?

21. Eight-Color Asteroid Survey(1980s)

22. Modern Asteroid Spectroscopy

23. Mineral Spectra

25. Modern Asteroid Spectra

26. Overlapping overtones of H2O/OH at 3 microns, from 2.6–2.85 lost to atmosphere

27. 951 Gaspra

28. Dactyl

29. 433 Eros

30. 253 Mathilde

31. 1999 JM8

32. Transmitted wave Echo from distant object radar astronomy The basics: A radar transmitter transmits radio waves at a known frequency for a certain time interval. The waves hit the object, bounce off of it, and return to the telescope. The receiver, now moved into the focus of the telescope, detects the weak echo.

33. Planetary Radar • Absolute calibration to speed of light. • Extremely high fractional precision. • Astronomical Unit. • And thus all parallax-based distance measurements. • Rotation rate of Mercury. • Not sun-synchronous. • Images of Venus. • Tests of general relativity. • Ice at the poles of Mercury.

34. Ice at the Poles of Mercury

35. Ice at the Poles of Mercury

36. 080503 5 asteroid experiments • Two main types of radar experiments can be performed on asteroids • Continuous Wave Experiments • Uses continuous 2380 MHz wave • Produces one-dimensional spectra • Provides information on rotational velocity, composition, and orbit of asteroid • Ranging Experiments • Uses encoded 2380 MHz wave • Produces 2D Delay-Doppler images • Provides information on size, shape, and spin state of asteroid

37. V time 080503 6 continuous wave • For continuous wave (CW) experiments, we send a constant, umodulated 2380 MHz signal • Upon reflection, the echo consists of many waves of slightly different frequencies • It is Doppler shifted as a result of the rotation of the asteroid Fourier transform the echo to get the spectrum

38. 1998 FH12 deviation from noise BW Hz from ephemeris 080503 7 asteroid spectra • A spectrum is obtained by taking the Fourier transform of the echo • Gives the strength of each reflected frequency • Determine resolution after data has been taken! • From the bandwidth, one can determine the rotational velocity of the asteroid moving away moving toward

39. Direction of radar illumination Doppler shift range Direction of radar illumination 13 080503 asteroid images • Delay Doppler images map a 3D object into a 2D image • Circles: Represent lines of constant range • Lines: Represent lines of constant Doppler shift

40. Doppler shift range 13 080503 asteroid images • Delay Doppler images map a 3D object into a 2D image • Circles: Represent lines of constant range • Lines: Represent lines of constant Doppler shift • Like cutting a potato up into many individual pieces (or pixels)

41. #1 #2 #3 pole asteroid images • One important piece of information we obtain from the Delay-Doppler images is the size of the asteroid • The extent of the asteroid in range indicates its radius Knowing the size and rot. velocity of the asteroid gives its period r • The frequency resolution is selected after the data has been collected by adjusting the FFT length • The range resolution is fixed by the sampling rate • Common sampling rate for image = 100ns (or 15 m)

42. Changing Frequency Resolution • Can rescale frequency to increase SNR of fast rotator. • Eye is pretty good at picking out linear structure anyway.

43. MODEL OF 216 KLEOPATRA FROM ARECIBO RADAR DELAY-DOPPLER IMAGES COLOR CODED FOR GRAVITATIONAL SLOPES

44. 2003 YT1 May 2 May 3

45. 2001 SN263 12 13 14 18 21 23 24 26

46. 2001 SN263

47. 1999 KW4 viewed in orbit plane

48. 1996 HW1

49. Internal Structure • We measure Shape and Spin, which provide information on internal structure. • Sphere strengthless • Slowly-rotating bar tidally stretched (strengthless)? • Fast-rotating bar at least some tensile strength • Very irregular collisional fragment? • The gross physical structure of NEAs is critical to all of the conventional reasons for studying them: • Meteorite delivery Space resources • Hazard mitigation • We see all kinds, implying multiple formation mechanisms

50. Summary: Variety • In spite of our attempt to classify NEAs, the clearest observation is their great Variety. • Spacecraft images can be more detailed than radar images, and can be more complete, but the vastly larger number of objects observable by radar allows us to detect and explore this variety. • Radar imaging can be used to aid in spacecraft target selection, and to identify the most interesting targets for further study.