1. GEOL3045: Planetary Geology Lysa Chizmadia Earth-Crossing Asteroids 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  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  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  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  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  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  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  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: Nakmura et al. 2001 Image from: Sasaki et al. 2001 Nature v410 p555-557

9. Summary  Three types of Earth-crossing asteroids:  Aten (a 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   Three types of Earth-crossing asteroids:  Aten (a 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 