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