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Asteroids & Meteorites
20 October 2014
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
• 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
Kirkwood Gaps
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 weatheringfamily, first ID of
(Phobos-like) effects documented asteroid ‘moons’
C Asteroids (‘carbonaceous’)• 253 Mathilde; 66 x 48 x 46 km, visited by NEAR Shoemaker
• Surface as dark as charcoal; typical outer belt asteroid
Ida and Dactyl
Itokawa
Hyabusa samples Itokawa
HyabusaReturnsJune 2010
Steins 2008
Toutatis
Vesta, Ceres, Moon
Dawn Mission at Vesta
Vesta Craters
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
Meteorites
Chondrite
Achondrite
Martian
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
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 weatheringfamily, first ID of
(Phobos-like) effects documented asteroid ‘moons’
C Asteroids (‘carbonaceous’)• 253 Mathilde; 66 x 48 x 46 km, visited by NEAR Shoemaker
• Surface as dark as charcoal; typical outer belt asteroid
Chixulub, Yucatan penninsula, Mexico
Gravity map of buried structure180 miles across; 65 millions years oldIdentified in early 1990s with seismic data, after 10 year ‘search’
Tunguska, Siberia, June 30, 1908
Black and white photos taken during field expedition in 1927; color photo taken in 1990
Jackson Hole Fireball, August 10, 1972
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)
Hoba Iron• 3m x 2m x 1m; 60+ tons• Found 1920, Namibia• No crater, classified ataxite
Ordinary Chondrites (S Asteroids?)
Three Views
of Vesta
• Hubble image, model and color-shaded topography
• Largest member of V class of asteroids (vestoids)
• Spectral variations consistent with HEDs
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
Meteor showers• Time
exposure image, tracking stellar motion
• Stars stay still, meteorites make trails
The Peekskill (NY) Fireball
P Jenniskens et al. Nature 458, 485-488
(2009)
Macroscopic features of the Almahata Sitta meteorite.
Chondrites
• Rocky, inhomogeneous, contain round “chondrules”
Microscope Microscope imageimage
Iron meteorites: from core of differentiated asteroids
Stony-Iron meteorites - the prettiest
• Crystals of olivene (a rock mineral) embedded in iron
• From boundary between core and mantle of large asteroids?
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