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GEOL3045: Planetary Geology

GEOL3045: Planetary Geology. Lysa Chizmadia Earth-Crossing Asteroids. Introduction. Three groups: Aten asteroids Named for 2062Aten Semi-major axis < 1AU (average distance) Apollo asteroids Named for 1862Apollo Semi-major axis > 1AU Amor asteroids Named for 1221Amor

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GEOL3045: Planetary Geology

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  1. GEOL3045: Planetary Geology Lysa Chizmadia Earth-Crossing Asteroids

  2. Introduction • Three groups: • Aten asteroids • Named for 2062Aten • Semi-major axis < 1AU (average distance) • Apollo asteroids • Named for 1862Apollo • Semi-major axis > 1AU • Amor asteroids • Named for 1221Amor • Between Mars & Earth • Semi-major axis 1.0-1.5 AU

  3. Aten Asteroids • Semi-major axis <1AU • Closest population to Sun • Orbits highly eccentric • Usually aphelion >1 AU • Aphelion <1 AU called Apohele • Only two known Apoheles Image from: http://www.daviddarling.info/encyclopedia/A/Aten_group.html

  4. Apollo Asteroids • Semi-major axis >1 AU • Perihelion <1.1017 AU • True Earth-crossers • Some get very close to Earth • Some even between Earth & Moon • Largest is 1866Sisyphus • Diameter ~10 km

  5. Amor Asteroids • Between Mars & Earth • Semi-major axes 1.0-1.5 AU • Mars-crossers • Mars at ~1.3 AU • Phobos & Deimos are probably Amor asteroids Image from: http://www.daviddarling.info/encyclopedia/A/Amor_group.html

  6. S- & Q-type Asteroids • 17% of asteroids • 2nd most common type • Moderately bright • Albedo 0.10 - 0.22 • Fe metal & Mg-silicates • Q-type most similar to Ordinary chondrites • S-types related to Q-types • Space weathering

  7. Asteroids Spectra • Q-type vs. S-type • Ordinary Chondrites Image from: Chapman 2004 Ann. Rev. Earth & Planet. Sci. v32, p539-567 Image from: Ueda et al. 2003 LPSC XXXIV #2078

  8. Space Weathering • S-type spectra from Q-type spectra • Reddening • Due to interaction of solar wind with silicate minerals • Results in amorphous material with Fe metal Image from: Sasaki et al. 2001 Nature v410 p555-557 Image from: Nakmura et al. 2001

  9. Summary • Three types of Earth-crossing asteroids: • Aten (a < 1AU; aphelion > 1 AU) • Apollo (a > 1AU; q < 1.017 AU) • Amor (a = 1.0-1.5 AU) • Similar spectra to ordinary chondrules • Q-type asteroids  • S-type asteroids  Space Weathering 

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