18. asteroids - institute for astronomybarnes/ast241_f13/an1.pdf · 2013-11-02 · large asteroids...
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Astronomy 241: Foundations of Astrophysics I
18. Asteroids
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100 AU
5 AU
S
20,000 AU
Overview: Structure
Inner system: terrestrial planets, asteroids.
Outer system: giant planets and moons, “KBOs”.
Oort Cloud: comets.
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Asteroids and comets to scale
Comet Nuclei
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Samples From the Asteroid Belt
Primitive meteorites are relics of the solar system’s formation, 4.6 Gyr old.
Processed meteorites come from differentiated asteroids, later broken up by collisions.
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Element Abundances
The Solar System
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The Last Global Rotation Movie
Mission to Eros
Eros: The Final Approach
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Asteroid Light Curves
An Asteroid Rotation Factory
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Diameter vs Rotation Rate
Some asteroids are rubble piles: loose collections of fragmented rock held together by self-gravity.
Spin Limits of Solar System Bodies
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Diameter vs Rotation Rate
Some small asteroids rotate so fast that they must be monoliths held together by material strength.
Spin Limits of Solar System Bodies
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PIA15678: Full View of Vesta
Giant Asteroids
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Giant Asteroids
Vesta
Largest Asteroid May Be 'Mini Planet'
Ceres975 km
Large asteroids are complex objects which appear to have differentiated.
530 km
PIA14321: Vesta Full Rotation Movie PIA15510: Vesta's Internal Structure
Basaltic crust
Mantle
Iron-Nickel core
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Wikipedia: Asteroid belt
Jupiter
Hildas
Trojans
Trojans
Mars
Belt Structure 14 August 2006
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Trojans
Mars
Jupiter
Trojans
Hildas
Belt Structure
Inner Belt: a < 2.5 AU
Mid Belt: 2.5 AU < a < 2.8 AU
Outer Belt: a > 2.8 AU
Wikipedia: Asteroid belt
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Kirkwood Gaps
Inne
r
Mid
dle
Out
er
Troj
ans
Hild
asResonances with Jupiter group asteroids by orbit period; period determines semi-major axis (Kepler III: P2 = a3).
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Jupiter
Hildas
Mars
Trojan Asteroids
L4
L5
Wikipedia: Asteroid belt
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Orbits starting near L4
ma/mb = 49
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Orbits starting near L1
ma/mb = 49
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SMBC 3127 (revised)
Points 4, 5 unstable in:(a) Pluto-Charon system
(MC / MP > 0.04)(b) Earth-Moon system (other planets perturb)
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Wikipedia: Hilda family
Hilda Asteroids
2:3 MMR; stable since they avoid Jupiter (e ~ 0.3).
Small inclinations (i ≲ 20°).Wikipedia: Hilda family
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Asteroid Belt Populations
Asteroid Families
Many asteroids are members of families; they have similar orbits and compositions (indicated by colors).
Inner belt asteroids (left) and families (right).
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Wikipedia: Asteroid belt
Trojans
Mars
Jupiter
Trojans
Hildas
Origin of Families
Fragments are scattered on similar orbits.
Large Asteroid Breakup — Don Davis
WHAM!
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Suspected Asteroid Collision Leaves Odd X-Pattern of Trailing Debris
A Suspected Asteroid Collision