Chapter 12

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University of Toronto St. George
Astronomy & Astrophysics
Clifford Orwin

Chapter 12: Asteroids, Comets, and Dwarf Planets Nov62010 12.1 Asteroids and Meteorites Asteroids, comets, + meteorites are scraps left over from formation of solar system (S.S.) Gives understanding of how planets + larger moons came to exist. Asteroids are planetesimals left over from birth of solar system. Meteorites: Pieces of rock that have fallen to ground from space. Most meteorites = pieces of asteroids that orbited Sun for billions of yrs bef. falling to Earth. Asteroids orbit calculated by law of gravity (Section 4.4). Ceres: Largest asteroid in SS (under 1000km in diameter). Probably more than a million asteroids w diameters > 1 km. If all asteroids compressed together + compressed into sphere by gravity then = object < 2000 km in diameter. If asteroid is relatively large, gravity can mold its solid rock into spherical or near- spherical shape. *Only Ceres is large enough for gravity to have compressed it into roughly spherical shape Thus Ceres is qualified as dwarf planet. Asteroids (like moons + planets) have many craters Thus they have also been battered. Mathilde: Asteroid w huge crater in centre Most likely bound (by gravity) rubble pile bc impact that made that crater would have shattered it. Asteroids shine with reflected sunlight brightness depends on (1) Size (2) Distance (3) Reflectivity. Asteroids distance can be determined from its position in orbit. Asteroids reflectivity determined by comparing asteroids brightness in visible light to brightness in infrared light Visible light is reflected sunlight while infrared is thermal radiation emitted from asteroid itself. Thus infrared brightness depends on temperature which depends on how much sunlight it absorbs Thus comparison btw.
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