Design of a Locomotive Engine for Dalian Locomotive

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Understanding the Formation Location of Meteorite
Parent Bodies
William Bottke Southwest Research
Institute Boulder, Colorado
Additional Thanks to Hal Levison, Alessandro
Morbidelli, David Nesvorny, Matthew Gounelle
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Meteorites and Their Parent Bodies

• Fact Nearly all meteorites come from the main
  belt.
• Irons, stony-irons, ordinary and carbonaceous
  chondrites, achondrites, etc.

Jupiters Orbit
Asteroid Belt
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Part 1The Standard Model
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Classical Main Belt Evolution
Main Belt Zone

• Assumption All meteorite parent bodies formed in
  the asteroid belt (2.0-3.2 AU).
• If true, the solar nebula experienced radical
  changes within a span of 1 AU.

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Taxonomic Stratification in Early Main Belt

• The early main belt was stratified into more
  heated (S, C) and more primitive (C, D/P)
  taxonomic groups.

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Mixing of Taxonomic Types
Gradie and Tedesco (1982)
Early Main Belt
D gt 50 km
S
C
P
Semimajor axis (AU)

• Large asteroids (D gt 50 km) show depletion (gt
  99) and radial mixing among taxonomic types.
• Both likely produced by gravitational
  interactions between planets, planetary embryos
  and planetesimals.

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Part 2Problem Where Do Iron Meteorites Come
From?
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Iron Meteorites

• Irons represent two-thirds of the unique parent
  bodies represented in our meteorite collection.
• They sample the cores of small differentiated
  asteroids (D lt 200 km) and are 1-2 My older than
  chondrules.
• Collisions of some form are needed to extract
  core material from their parent bodies.
• This should produce mantle (olivine) and crust
  (basaltic) fragments.

Sample references Burbine et al. (2002) Scott
(2002) Kleine et al. (2005) Asphaug et al.
(2006)
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We Infer From Meteorites That
Small Differentiated Parent Bodies (and Their
Fragments) Should Be Common in the Main Belt!
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Observations of Main Belt Asteroids
?

• (4) Vesta is the only known intact differentiated
  asteroid.
• Asteroid families show no obvious signs of
  silicate melting (i.e., no obvious core,
  mantle, crust).
• Few asteroids are fragments from differentiated
  bodies (some V-, A-, M-types).

Sample references Burbine and Binzel (2002) Bus
and Binzel (2002a,b) Cellino et al. (2002)
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We Infer From Asteroids That
?
Little Differentiation Ever Occurred in the Main
Asteroid Belt!
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Questions Answers

• How can we reconcile these differences?
• Meteorites Small differentiated asteroids were
  once common.
• Asteroids Little differentiation ever occurred
  in main belt.

Perhaps the Parent Bodies of Iron Meteorites
Formed and Fragmented Elsewhere
Wetherill and Wasson (1979) Bottke et al. (2006)
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Differentiation in Terrestrial Planet Region
Main Belt Zone
Melting Zone?

• 26Al produces heat but decays quickly (t1/2
  0.73 My).
• Only fast-growing planetesimals have a chance to
  melt.
• Growth is a function of heliocentric distance and
  swarm density.
• Until we reach snowline, the fastest-growing
  planetesimals are close to Sun.

Solves many problems, but can we get bodies to
main belt?
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Inner Solar System Planetesimals

• Evolution of inner solar system planetesimals
• No Jupiter!
• Planetary embryos (0.5-3.0 AU) perturb
  planetesimals.
• Small number are scattered into the stable main
  belt zone.
• Excitation will produce collisional evolution.

0.5-1.0 AU
1.0-1.5 AU
1.5-2.0 AU
Embryos
Bottke et al. (2006)
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Fraction Reaching Main Belt Zone

• Planetesimals/fragments from inner solar system
  can reach the main belt before Jupiter forms.

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Fraction Reaching Main Belt Zone
Most are located in the inner main belt, the most
likely region to produce meteorites!
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Part 3Where Do Primitive Meteorites Come From?
Where Did They Originate?
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Are Micrometeorites From Comets?

• Most unmelted MMs are similar to primitive
  chondrites (e.g., CI, Tagish Lake)
• Primitive meteorites came from asteroid belt.
• If they are from asteroids, why are so few MMs
  ordinary chondrites?
• If from comets, how did they arrive unmelted?

Levison, Bottke, Gounelle, Morbidelli, Nesvorny,
and Tsiganis (2008)
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Some Comet Material Looks Asteroidal
Hypervelocity Dust Particle Capture into Aerogel
Ferro- Magnesian Silicates, Metal Sulfides,
Refractory Carbon, Carbonates

• STARDUST samples most closely resemble primitive
  chondritic meteorites from the asteroid belt.

Ishii et al. (2008)
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P and D-Type Asteroids Look Like Dormant Comets
Gradie and Tedesco (1982)
D gt 50 km

• P/D-type asteroids are low albedo objects with
  flat-to-red featureless spectra. They are
  similar to dormant comets.
• Did they form there, or did something else take
  place?

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New Solar System Formation Model (Nice Model)
Comets

• Old view. Gas giants/comets formed near present
  locations (5-30 AU) and reached current orbits
  4.5 Gy ago.

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New Solar System Formation Model (Nice Model)
Comets

• Old view. Gas giants/comets formed near present
  locations (5-30 AU) and reached current orbits
  4.5 Gy ago.

Primordial disk of comets

• New view. Gas giants formed in more compact
  formation between 5-15 AU. Massive comet
  population of 35 Earth masses existed between
  16-30 AU.

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Destabilizing the Outer Solar System
Tsiganis et al. (2005) Morbidelli et al. (2005)
Gomes et al. (2005)
Watch what happens after 850 My!
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Things to Like About the Nice Model

• So far, the Nice model can explain
• The orbits of the Jovian planets.
• The mass and orbital distribution of the Trojan
  asteroids, Kuiper belt objects, and irregular
  satellites.
• Why the planets (and the Moon!) experienced a
  Late Heavy Bombardment 3.9 Gy ago.

The Nice Model is described in 3 Nature papers
Tsiganis et al. (2005)
Morbidelli et al. (2005) Gomes et al. (2005)
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Planet Migration and the Asteroid Belt
Comet Disk
Asteroid Belt

• As the planets migrated, so did their resonances.
  
• Many asteroids (90) and most comets were lost
  by planetary interactions and sweeping
  resonances.

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Planet Migration and the Asteroid Belt
Comet Disk
Asteroid Belt

• A smaller fraction, however, may have been
  trapped by resonant interactions in dynamically
  stable locations.

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Inner Solar System Asteroids

• Observed asteroids with a 2.0-5.2 AU

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Inner Solar System Asteroids
Inner MB
Outer MB
Hildas (J32)
Trojans (J11)

• We sub-divided them into 4 populations.

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Inner Solar System Asteroids
Inner MB
Outer MB
Hildas (J32)
Trojans (J11)

• 1.2 million bodies were tracked during planet
  migration.

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Comets in the Asteroid Belt
Captured Comets Right After Migration
Inner MB
Outer MB
Hildas (J32)
Trojans (J11)

• 1270 were captured on orbits decoupled from
  Jupiter.

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Comets in the Asteroid Belt
Captured Comets 100 My After Migration
Trojans (J11)
Inner MB
Outer MB
Hildas (J32)

• Many objects are unstable and escape over a few
  100 My.

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Comets in the Asteroid Belt
Captured Comets 3.9 Gy After Migration
Inner MB
Outer MB
Hildas (J32)
Trojans (J11)

• These captured objects were stable over 3.9
  billion years.

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Comparison with Some Observed D-Types
D-type spectra from D. Tholen and S. J. Bus
databases
D-types

• The orbital match with these D-type asteroids is
  good!

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Collisional Disruption of Captured Comets
Impact into Rubble-Pile Object

• Comets are likely weak.
• Impacts with asteroids should disrupt many main
  belt comets over 3.9 Gy!
• Lots of small particles should be produced!

Durda, Bottke et al. (2006)
Reference for weak comets Leinhardt and
Stewart-Mukhopadhyay (2008)
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Micrometeorite Production Dominated By Comets
Embedded in Asteroid Belt
Main Belt Comets
Main Belt Asteroids
Trojans
Hildas
Levison et al. (2008)

• Dust production from disrupted comets dominates
  other main belt sources by factor of 2-4.

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Conclusions

• The parent bodies of many primitive meteorites
  may have originated in the outer solar system (gt
  15 AU) and may be related to comets and Kuiper
  belt objects.
• MB comet breakups may dominate asteroid belt dust
  production.
• This may explain why so many unmelted
  micrometeorites look primitive (e.g., CIs and
  Tagish Lake) and so few look like ordinary
  chondrites.
• Many differentiated meteorites come from parent
  bodies that may have formed in the terrestrial
  planet region (lt 2 AU).
• Are the OCs and metamorphosed CC (e.g., CV, CO)
  the only meteorites indigenous to the main belt
  region?