Astronomy 241: Foundations of Astrophysics I 27. Asteroids
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Astronomy 241: Foundations of Astrophysics I
27. Asteroids
Overview: Structure
Inner system: terrestrial planets, asteroids.
Outer system: giant planets and moons, “KBOs”.
Oort Cloud: comets.
Samples From the Asteroid Belt
Primitive meteorites are relics of the solar system’s formation 4.6 Gyr ago.
Processed meteorites come from differentiated asteroids, later broken up by collisions.
Asteroid Light Curves
Wikipedia: Light Curve
(Days)
Period
Diameter vs Rotation Rate
Most asteroids are rubble piles: loose collections of fragmented rock held together by self-gravity.
Planetary Sciences, Fig. 9.20
PIA15678: Full View of Vesta
Giant Asteroids
Giant Asteroids
Vesta
Largest Asteroid May Be 'Mini Planet'
Ceres
Giant 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
975 km
PIA19547: Ceres Rotation
Wikipedia: Asteroid belt
Jupiter
Hildas
Trojans
Trojans
Mars
Belt Structure 14 August 2006
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
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).
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).
Wikipedia: Asteroid belt
Trojans
Mars
Jupiter
Trojans
Hildas
Origin of Families
Fragments are scattered on similar orbits.
Large Asteroid Breakup — Don Davis
WHAM!
Suspected Asteroid Collision Leaves Odd X-Pattern of Trailing Debris
A Suspected Asteroid Collision
Jupiter
Hildas
Mars
Trojan Asteroids
L4
L5
Wikipedia: Asteroid belt
Orbits starting near L4
ma/mb = 49
Orbits starting near L1
ma/mb = 49
SMBC 3127 (revised)
Points 4 and 5 are usually stable.
They are unstable in:(a) Pluto-Charon system
(MC / MP > 0.04)(b) Earth-Moon system (other planets perturb)
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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