GEOL3045: Planetary Geology Lysa Chizmadia Earth-Crossing Asteroids 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  Between Mars & Earth  Semi-major axis 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 AU

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:

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

Amor Asteroids  Between Mars & Earth  Semi-major axes AU  Mars-crossers  Mars at ~1.3 AU  Phobos & Deimos are probably Amor asteroids  Between Mars & Earth  Semi-major axes AU  Mars-crossers  Mars at ~1.3 AU  Phobos & Deimos are probably Amor asteroids Image from:

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

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, p Image from: Ueda et al LPSC XXXIV #2078

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 Image from: Sasaki et al Nature v410 p

Summary  Three types of Earth-crossing asteroids:  Aten (a 1 AU)  Apollo (a > 1AU; q < AU)  Amor (a = 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 < AU)  Amor (a = AU)  Similar spectra to ordinary chondrules  Q-type asteroids   S-type asteroids  Space Weathering 