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Asteroids

Asteroids. Types of Asteroids. Asteroids are classified according to their chemical make-up: C-types S-types P and D-types. C Type Asteroids. comprise about 75% of all known asteroids Dark objects == albedo of about 0.03 Composition resembles carbonaceous meteorites.

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Asteroids

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  1. Asteroids

  2. Types of Asteroids • Asteroids are classified according to their chemical make-up: • C-types • S-types • P and D-types

  3. C Type Asteroids • comprise about 75% of all known asteroids • Dark objects == albedo of about 0.03 • Composition resembles carbonaceous meteorites. • Ceres and Pallas are C Type

  4. C Types Continued… • Spectra indicates presence of hydrated minerals • Weak absorption from iron in phyllosilicates and organic matter • These features mean that they are probably carbonaceous • Water contents seems to go down in larger bodies = represent heated cores? • Spectrum of Pallas resembles CR chondrites = parent body for this chondrite group?

  5. Ceres

  6. S Type Asteroids • S-type asteroids comprise about 17% of all known asteroids • S-type asteroids are fairly bright == albedo of .10 to .22 • Composed of Ni and Fe, Fe and Mg sillicates • Majourity are achondritic or asteroids which we dont have samples for • Gaspra and Ida are an S-type asteroid.

  7. Gaspra and Ida

  8. D and P Type Asteroids • Darkest known objects • Spectra usually featureless, very reddened reflectance, low albedo • Composed of organic matter and opaque minerals • BUT don't show the ~3 micrometer absorption feature of hydrous alteration minerals = still frozen? • Pholus

  9. Where are they? • Inner portion of the main belt consists mostly of S type asteroids • 6 Hebe (H chondrite, ordinary chondrites) • C type in the middle main belt • Carbonaceous, ordinary • P and D types located at the Trojans and beyond • Positions = snow line

  10. Methods for Seeing • Asteroids change brightness due to their rotation • can use this to model the shape and rotation rate of the asteroid • Use Radiometry (heat sensing) • thermal vibrations are measured and used to detect heat leaving from poorly insulated buildings • Using assumptions about what the asteroids are made of we can determine their shape with a variation of this • Comparing thermal with visual brightness = size of asteroid • Silhouetting • Binary Eclipsing but with rocks… • Of course there is RADAR too: Castalia

  11. Spectrocopy • Spectrum of sunlight reflected from the surface of a mineral will be missing those wavelengths that are abs. by electrons, the exact wavelength being characteristic for certain atoms in specific kinds of minerals. • IE: Hydrogen gives off certain wavelengths and absorbs others and we get a spectra for hydrogen and that's how we know its hydrogen. • Result being...

  12. Spectroscopy continued… • We can use the spectra of various common meteorite samples • Coupled with spectra from asteroids • Determine whether the spectra are the same • In other words…

  13. Spectra of Minerals

  14. Spectrum of Asteroid

  15. 6 Hebe

  16. The Problem • Space Weathering • physical and chemical changes on the surface • Results from: • surface being bombarded • solar winds • Proof from Galileo Mission and 243 Ida

  17. Missions • Galileo (1991) • 951 Gaspra - irregular shape, low density of craters = young age • 243 Ida - heavily cratered • NEAR • Eros • Hayabusa • Itokawa

  18. NEAR Mission • Visit Eros • Regolith evidence • Complex/Diverse • Blocks and ponds spectra same as BG spectra • Homogeneity results of impacts and ejecta • Absence of small craters • Brr brr put on your warmies!

  19. Eros

  20. Eros

  21. Eros

  22. Eros

  23. Eros: Himeros • Curving trough at the top and upper right • subtle curving depressions near the bottom reflect fracturing of Eros • bright and dark banding near the top results from material accumulating at the base of the nearly vertical scarp that forms one wall of the curving trough • More subtle dark lines near the lower right result from thin layers of loose material moving down an approximately 20-degree slope. • Many impact craters dotting the area are somewhat eroded and infilled.

  24. Eros • Overall Mosaic of Eros • Colour of Regolith • Orbiting

  25. Hayabusa and Itokawa • Composition resembles a S(IV) or Q-types: similar to ordinary chondrites • Rubble pile • Heterogeneity of colour and albedo

  26. Itokawa

  27. Itokawa

  28. The End

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