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How can fragments from the asteroid belt reach Earth-crossing orbits?
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Meteor and meteoroid
The Cabin Creek meteorite, an iron (nickel-iron alloy) meteorite that was observed to fall in northwestern Arkansas on March 27, 1886. Its characteristic pattern of “thumbprint” dimples, or regmaglypts, is the result of melting and consequent ablation of its surface as it traveled through the atmosphere. The meteorite is likely a fragment of one of the M class asteroids, which show significant nickel-iron in their surface material.
Fragments from the asteroid belt reach Earth-crossing orbits primarily through gravitational interactions and specific physical effects that alter their trajectories. The following mechanisms are key to this process:
- Gravitational Resonances: The most significant mechanism involves Kirkwood gaps, which are regions in the asteroid belt depleted of objects due to mean-motion resonances with Jupiter. When an asteroid enters a resonance (such as the 3:1 resonance), it receives regular gravitational "nudges" from Jupiter. These repeated forces make the asteroid's orbit chaotic, eventually shifting its perihelion inside Earth's orbit.123
- Yarkovsky Effect: Small asteroids are subject to the Yarkovsky effect, a force resulting from the anisotropic emission of thermal radiation from their surfaces. This effect causes small bodies to drift slowly into Kirkwood gaps, where they then become susceptible to the gravitational perturbations mentioned above.14
- Collisional Fragmentation: Collisions between asteroids in the main belt are common. While most debris is pulverized, some fragments are ejected at velocities that can place them into Earth-crossing orbits, though this process is less efficient than resonance-driven transport.24
- Poynting-Robertson Drag: For very small particles (interplanetary dust), interaction with solar radiation causes them to spiral inward from the asteroid belt toward Earth-crossing orbits over thousands of years.2