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Asteroids & Meteorites

Asteroids & Meteorites. 23 October 2013. Asteroids. Apollo. Trojans. Asteroid Belt as viewed from Above. Over 100,000 objects greater than 10 km. now identified in the Main Belt Total mass less than 1% of moon’s mass

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Asteroids & Meteorites

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  1. Asteroids & Meteorites 23 October 2013

  2. Asteroids Apollo Trojans

  3. Asteroid Belt as viewed from Above • Over 100,000 objects greater than 10 km. now identified in the Main Belt • Total mass less than 1% of moon’s mass • Over 100 NEAs greater than 1 km. across are being tracked; probably part of a population of about 2000 • Kirkwood gap (and others) occur in the belt where there are orbital resonances with Jupiter • Asteroids classified by ‘spectral group

  4. Kirkwood Gaps

  5. S Asteroids (‘silicaceous’) • 951 Gaspra 433 Eros (true color) Ida (and Dactyl) • 19 x 12 x 11 km 33 x 13 x13 km 58 x 23 km (1km) • Galileo flyby, 199 NEAR orbit/landing Galileo flyby, 1993 • Grooves, curved near-Earth asteroid, member of Koronis depressions, ridges space weathering family, first ID of (Phobos-like) effects documented asteroid ‘moons’

  6. C Asteroids (‘carbonaceous’) • 253 Mathilde; 66 x 48 x 46 km, visited by NEAR Shoemaker • Surface as dark as charcoal; typical outer belt asteroid

  7. Ida and Dactyl

  8. Itokawa

  9. Hyabusa samples Itokawa

  10. Hyabusa Returns June 2010

  11. Steins 2008

  12. Toutatis

  13. Vesta, Ceres, Moon

  14. Dawn Mission at Vesta

  15. Vesta Craters

  16. Asteroids Summary • Solid objects mostly in a belt between Mars and Jupiter • Small bodies much more common than larger ones • Classes similar to meteorites: Stony (S), Carbonaceous (C), Metallic (M) • Bodies and belts shaped by collisions, resonances • Source of meteorites

  17. Achondrite

  18. Martian

  19. Asteroid Belt as viewed from Above • Over 100,000 objects greater than 10 km. now identified in the Main Belt • Total mass less than 1% of moon’s mass • Over 100 NEAs greater than 1 km. across are being tracked; probably part of a population of about 2000 • Kirkwood gap (and others) occur in the belt where there are orbital resonances with Jupiter • Asteroids classified by ‘spectral group

  20. S Asteroids (‘silicaceous’) • 951 Gaspra 433 Eros (true color) Ida (and Dactyl) • 19 x 12 x 11 km 33 x 13 x13 km 58 x 23 km (1km) • Galileo flyby, 199 NEAR orbit/landing Galileo flyby, 1993 • Grooves, curved near-Earth asteroid, member of Koronis depressions, ridges space weathering family, first ID of (Phobos-like) effects documented asteroid ‘moons’

  21. C Asteroids (‘carbonaceous’) • 253 Mathilde; 66 x 48 x 46 km, visited by NEAR Shoemaker • Surface as dark as charcoal; typical outer belt asteroid

  22. Gravity map of buried structure 180 miles across; 65 millions years old Identified in early 1990s with seismic data, after 10 year ‘search’ Chixulub, Yucatan penninsula, Mexico

  23. Tunguska, Siberia, June 30, 1908 Black and white photos taken during field expedition in 1927; color photo taken in 1990

  24. Jackson Hole Fireball, August 10, 1972

  25. Potentially Hazardous Asteroid ThreatSize-frequency diagram for impacting objects • ~100 tons of meteroritic dust falls each day • 50 m impactor once per 1000 yr (local effects) • 500 m impactor once per million years (regional effects) • 5 km. impactor once per 100 million years (global effects)

  26. Hoba Iron • 3m x 2m x 1m; 60+ tons • Found 1920, Namibia • No crater, classified ataxite

  27. Ordinary Chondrites (S Asteroids?)

  28. Three Views of Vesta • Hubble image, model and color-shaded topography • Largest member of V class of asteroids (vestoids) • Spectral variations consistent with HEDs

  29. What were the processes and products in the early Solar System (Meteoritics, 2004) • Impact features on all planetary surfaces; planets formed by accretion of planetesimals from a turbulent solar nebula • Much mixing of components; completed in 5-10 million years • ‘Residual’ debris forms asteroid belt; Kuiper belt, Oort cloud

  30. Meteor showers • Time exposure image, tracking stellar motion • Stars stay still, meteorites make trails

  31. The Peekskill (NY) Fireball

  32. Macroscopic features of the Almahata Sitta meteorite. P Jenniskens et al.Nature458, 485-488 (2009)

  33. Chondrites • Rocky, inhomogeneous, contain round “chondrules” Microscope image

  34. Iron meteorites: from core of differentiated asteroids

  35. Stony-Iron meteorites - the prettiest • Crystals of olivene (a rock mineral) embedded in iron • From boundary between core and mantle of large asteroids?

  36. The main points: Meteorites • Each year the Earth sweeps up ~80,000 tons of extraterrestrial matter • Some are identifiable pieces of the Moon, Mars, or Vesta; most are pieces of asteroids • Meteorites were broken off their parent bodies 10’s to 100’s of million years ago (recently compared to age of Solar System) • Oldest meteorites (chondrites) contain interstellar dust, tiny diamonds made in supernova explosions, organic molecules and amino acids (building blocks of life) • Direct insight into pre-solar system matter, solar system formation

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