Tru Physics

Yarkovsky Effect

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Introduction

The Yarkovsky Effect is the force acting on a rotating body in space caused by the anisotropic emission of thermal photons (which carry momentum). This effect is named after the engineer Ivan Osipovich Yarkovsky, who first proposed the idea. This effect plays a significant role in the dynamics of small celestial bodies, such as asteroids and meteoroids.

Understanding the Yarkovsky Effect

The Yarkovsky effect operates on the principle of heat absorption and emission. When a celestial body, like an asteroid, rotates, the surface that is exposed to the Sun heats up and absorbs solar radiation. As this surface rotates out of the sunlight and cools down, it emits this heat in the form of infrared radiation.

Due to the finite speed of light, there is a time lag between the absorption and re-emission, which results in the re-emitted radiation being sent off at an angle away from the Sun. This carries away momentum and provides a tiny thrust. This effect can be summarized as follows:

F = \dfrac{dp}{dt} = \dfrac{d}{dt}(m v) = \dot{m} v + m \dot{v}

where F is the force, dp/dt is the rate of change of momentum, m is the mass, v is the velocity, \dot{m} is the rate of mass loss, and \dot{v} is the acceleration.

Types of Yarkovsky Effect

The Yarkovsky Effect can be split into two types depending on whether the body’s rotation is prograde or retrograde:

  • Diurnal Effect: For a body rotating with a prograde spin (same direction as its orbit), the re-emitted thermal radiation pushes the body along its path of motion.
  • Seasonal (or Secular) Effect: For a body rotating with a retrograde spin (opposite direction to its orbit), the re-emitted thermal radiation pushes the body against its path of motion.

Importance of the Yarkovsky Effect

Although the force exerted by the Yarkovsky Effect is minuscule, it can cause significant changes in the orbit of small celestial bodies over long timescales. It is particularly important in the field of asteroid dynamics and is considered in long-term predictions of asteroid orbits and their potential Earth impacts.

Conclusion

The Yarkovsky Effect is a subtle but important force that affects the orbits of small celestial bodies. Understanding this effect is vital for accurately predicting the long-term evolution of these bodies and assessing any potential threats to Earth.

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