Meteorite Composition

Meteorite Composition

Introduction to Meteorites

• Meteorites largely originate from the asteroid belt.
• Impact velocities from the asteroid belt are typically around $14 {km/s}$.

Daniel Barringer

• Daniel Barringer (1860-1929) was a mining engineer.
• He discovered the Commonwealth silver mine near Pearce, Arizona.
• The mine produced 12 million ounces of silver, providing Barringer with a considerable fortune.
• Barringer's initial interest in the crater was primarily economic.

Meteorite Classification

• Meteorites are classified into three main types based on composition:
  • Stony: 94.6% of meteorites that fall to Earth.
    • Chondrites: 86.2%
      • Ordinary Chondrites: 80%
        • H: 33.9% (High Iron)
        • L: 37.0% (Low Iron)
        • LL: 9.1% (Low Low Iron)
      • Carbonaceous Chondrites: 4.4%
    • Achondrites: 8.2%
  • Stony Iron: 1.0%
  • Iron: 4.4%

Stony Meteorites

Chondrites

• Ordinary Chondrites:
  • John Bortle, 1992, studied ordinary chondrites.
  • Parent body: S-Type asteroids
  • Have been heated, but not enough to fully differentiate.
  • Occur most frequently at the inner edge of the asteroid belt (17% of known asteroids).
  • H-Type (High Iron):
    • Iron content: ~ 25 – 31%
    • Nickel-iron (metallic): 15 – 19%
    • Contains Olivine $(Fe<em>2SiO</em>4)$.
  • L-Type (Low Iron):
    • Iron content: ~ 20 – 25%
    • Nickel-iron (metallic): 4 – 10%
    • Contains Olivine $(Fe<em>2SiO</em>4)$.
    • Other rocky minerals.
  • LL-Type (Low Low Iron):
    • Iron content: ~ 19 – 22%
    • Nickel-iron (metallic): 0 – 3%
    • Contains Olivine $(Fe<em>2SiO</em>4)$.
    • Lots of other rocky minerals.
  • S-Type Asteroid Economics and Utilization
    • Contain numerous metals: nickel, cobalt, gold, and platinum.
    • A small 10-meter S-type asteroid contains about 650,000 kg (1,433,000 lb) of metal with 50 kg (110 lb) in the form of rare metals like platinum and gold.
    • VERY high priority target for initial mining.

Carbonaceous Chondrites

• Fell in Valle de Allende, Chihuahua, Mexico on February 8, 1969.
• Also fell on Christmas Island Sept 28, 1969.
• Murchison meteorite: Evidence for extraterrestrial amino-acids and hydrocarbons was found.
• Contain carbon-rich chondrules and matrix.
• The abundance of elements is very similar to the abundance in the Sun.
• Ages:
  • Radiometric ages are approximately 4.56 billion years old.
• Water Rich: 3% to 22%
• Rocky: Silicates, Oxides and Sulfides
• Rocks are often modified by water (Aqueous alteration)
• Rich in a mix of complex organic compounds such as amino-acids.
• The presence of volatile organic chemicals and water indicates that they have not undergone significant heating ($>200 {°C}$) since they were formed.
• Their compositions are considered to be close to that of the solar nebula from which the Solar System condensed.
• Presolar grains:
  • Diamond (C), graphite (C), silicon carbide (SiC).
  • Interstellar solid matter in the form of tiny solid grains that originated before the Sun was formed.
  • Have a chemical/elemental signature that shows they were not formed in our solar system.
• Parent Body:
  • C-Type asteroid (75% of known asteroids).
  • Have not undergone significant heating since they were formed.
  • Occur most frequently at the outer edge of the asteroid belt.
  • Parent bodies are smaller (and have always been smaller) than ~ 10 km in diameter
  • 3.5 AU - 80% C-type
  • 2 AU - 40% C-type
• C-Type asteroid economics and utilization
  • High abundance of water could be used in an exploration effort beyond the asteroid.
  • Mission costs could be reduced by using the available water from the asteroid.
  • Organic carbon, phosphorus, and other key ingredients for fertilizer which could be used to grow food.
  • Not a high priority target for initial mining.

Achondrites

• Basalt, Impact Breccia, Pristine Highlands
• Parent body: V-Type asteroid
• Surfaces of worlds that were geologically active.
• Occur most frequently at the very inner edge of the asteroid belt (6% of known asteroids).
• V-Type asteroid economics and utilization
  • Earth-Crust-like material
  • VERY low priority target for initial mining.

Iron and Stony-Iron Meteorites

• Iron/Stony-Iron parent body
  • M-Type asteroid
  • Cores of worlds that were geologically active.
  • Widmanstätten Pattern
  • Occur most frequently at the center of the asteroid belt (10% of known asteroids).
• Iron meteorite composition
  • Metallic Iron (N/A), Nickel ($1,000 {x} {⊕}$) Gold ($120 {x} {⊕}$), Platinum ($2,700 {x} {⊕}$)
    • ⊕ = Earth Crust
• M-Type asteroid economics and utilization
  • Numerous metals including: nickel, cobalt, gold and platinum.
  • 10 times more metal than S-Type asteroids
  • VERY high priority target for initial mining.

Asteroid Belt Overview

• Asteroids are small compared to the Moon.
• Total Mass of the Asteroid Belt:
  • 1 Ceres (29%)
  • 4 Vesta (8%)
  • 2 Pallas (7%)
  • 10 Hygiea (3%)
  • All Other Asteroids (53%)
• The vast majority of asteroids are small.
• For every 1 asteroid there are 10 asteroids 1/3 its size
• Size distribution of the Asteroid Belt? Look at the Moon.
  • There are far more small craters than large craters
  • There are far more small asteroids than large asteroids
• Known Asteroid Diameters:
  • Ceres: 952 km
  • Vesta: 525 km
  • Eros: 33km

Spacecraft Missions to Asteroids

• A list of spacecraft missions to various asteroids and comets is included, with details of the asteroids' sizes and the mission names.
  • 9969 Braille: 2.1 x 1 x 1 km; Deep Space 1, 1999

Asteroid Properties

*Minor planets: Period vs. Diameter

• VERY few asteroids with spin rate < 2 hr

Rubble Pile Asteroids

• Itokawa:
  • Considered a rubble-pile body because of its low bulk density, high porosity, boulder-rich appearance, and shape.
  • Early collisional breakup of a preexisting parent asteroid followed by a re-agglomeration into a rubble-pile object.
• Other examples:
  • Ryugu (Hayabusa2) (1 km)
  • Bennu (OSIRIS-REx) (500 m)
  • Dimorphos (200 m) (DART mission - Sep. 26, 2022)
• How would you move/mine a pile of rubble?