Asteroid 5261 Eureka Mars Trojan Frames taken 10

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

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

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.

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.

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

Near-Earth Asteroid Discoveries

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

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.

Meteorites Los Angeles Shergottite (Martian Meteorite) Meteorites provide samples of extraterrestrial bodies, but where did they come from? Korrabes H 3 Chondrite Origin Unknown

Bilanga Meteorite 5 mm across

Why Study Asteroids? ● Solar System Formation – ● Space Resources – ● Many asteroids are believed to be relatively unprocessed remnants of Solar-System formation 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

Impact Hazard Fig. 8 -28, p. 179

Where are the Asteroids?

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

Collisional Evolution

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?

Eight-Color Asteroid Survey (1980 s)

Modern Asteroid Spectroscopy

Mineral Spectra

Modern Asteroid Spectra

Overlapping overtones of H 2 O/OH at 3 microns, from 2. 6– 2. 85 lost to atmosphere

951 Gaspra

Dactyl

433 Eros

253 Mathilde

1999 JM 8

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. Transmitted wave Echo from distant object

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

Ice at the Poles of Mercury

Ice at the Poles of Mercury

asteroid experiments • Two main types of radar experiments can be performed on asteroids 1. Continuous Wave Experiments • • • Uses continuous 2380 MHz wave Produces one-dimensional spectra Provides information on rotational velocity, composition, and orbit of asteroid 2. Ranging Experiments • • • 080503 Uses encoded 2380 MHz wave Produces 2 D Delay-Doppler images Provides information on size, shape, and spin state of asteroid 5

continuous wave • For continuous wave (CW) experiments, we send a constant, umodulated 2380 MHz signal V time • 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 080503 6

asteroid spectra • deviation from noise 1998 FH 12 moving away BW 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 toward Hz from ephemeris 080503 7

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

asteroid images • Delay Doppler images map a 3 D object into a 2 D 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) Doppler shift range 080503 13

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 #1 #2 #3 r pole Knowing the size and rot. velocity of the asteroid gives its period • 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 = 100 ns (or 15 m)

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

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

2003 YT 1 May 2 May 3

2001 SN 263 12 13 14 18 21 23 24 26

2001 SN 263

1999 KW 4 viewed in orbit plane

1996 HW 1

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

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.

asteroid armageddon? Scientists also study asteroids because of the potential hazards they pose to the Earth: Asteroid impact* Airplane crash Likelihood of death 1 in 20, 000 Frequency of event 1 in 10, 000 years ~40 a year Number of casualties All life on Earth 1 -3000 people *Data based on a 7. 0 km asteroid.

Hazard per Year

Normalized Hazard

Comparison to Other Causes (Deaths per Year) ● Cancer 473 000 ● Falls ● Suicide 30 000 ● Drowning 5 000 ● Homicide 19 000 ● Fires/Burns 5 000 ● Car Crash 46 000 ● Falling objects 1 000 ● AIDS ● Impact 15 600 12 000 200 From Weissman (1994), “The Comet and Asteroid Impact Hazard in Perspective, ” in Hazards of Near-Earth Space, p 1191, and other sources

Preventable Deaths Worldwide average, normalized to US population. ● Vaccine Preventable Diseases 129 000 ● Antibiotic Preventable Diseases 225 000 ● Diarrhea 185 000 ● Globally Destructive Impact 200

What's the Comparison? ● ● Impact can cause global, civilization-destroying catastrophe. The whole is greater than the sum of its parts. Drama: Air travel is much safer than automobile travel, but people drive because they are afraid to fly. AIDS: Since the impact hazard came under study, AIDS became a clear worldwide hazard, and receives much more funding. Terrorism: Since the impact hazard came under study, terrorism became a clear worldwide concern (but perhaps not a hazard), and also receives much more funding.

Minimizing the Hazard ● ● Radar distance measurements improve our knowledge of the position of a “potentially hazardous” asteroid by orders of magnitude. Radar imaging of asteroids provides a “faster, cheaper” way to image these objects.