Poynting–Robertson effect

The Poynting - Robertson effect ( after John Henry Poynting and Howard Percy Robertson, the theoretically predicted him in the first half of the 20th century ) is due to the radiation pressure, the solar radiation exerts on the interplanetary matter, and causes the orbits smaller particles more and more closer to the sun.

Explanation

Because of the proper motion in its orbit around the sun to see all the body the incoming radiation from the sun by a small angle obliquely from the front coming (see also aberration) and are therefore decelerated by the radiation pressure, that is, its specific orbital angular momentum and their specific orbital energy decrease.

It is assumed that the release of energy through heat radiation in the rest frame of the body is isotropic, ie equally in all directions, is performed; then the emitted radiation does not affect the movement (in contrast to Jarkowski effect).

The radiation pressure in a radial direction, that is transverse to the direction of movement of the body is much higher than that of the movement of opposing component. About an orbit averaged, the radial component does not act, because that no change in the specific orbital angular momentum is connected. Only when the radiation pressure to the radial strength of the gravitational force, that the attraction by the sun, is similar, there will be slight modifications in the web but which is static and does not affect the dynamics of the Poynting Robertson effect. As soon as the pressure overcomes the radial radiation attraction by the sun, is not orbit around the sun, and a state of the particle is driven by the radiation pressure of the sun system. This applies to extremely small particles.

Effects on the interplanetary matter

While the Poynting - Robertson effect in larger bodies negligible, especially small particles of interplanetary dust (about 1 mm and smaller) are influenced by him. Due to the loss of specific orbital energy their tracks are always close to the sun and approach it in a spiral path. A particle of 1 micron radius required, for example, from the belt of asteroids around 10,000 years.

The particles vaporize or disintegrate into smaller particles before they reach the sun, then pushed away too small for the PR effect and by radiation pressure radially from the sun. The constant replenishment source for interplanetary matter is seen in the resolution of comets and the decay of minor planets.

Historical

Poynting explained the effect on the basis of today as misrecognized ether theory (' friction ' of isotropic particles by thermal radiation at the ether ). Robertson considered the effect of general - relativistic correct, but also the non- general relativistic derivation leads in the framework of the approximation v « c to the same result. All that matters is the momentum transfer of the photon of solar radiation on the dust particles, namely - as already mentioned above - the counter to the web unidirectional component.

Viewpoint of an observer at rest

Again and again to explain the braking effect declaration that radiated by the dust particles in the direction of movement photons have (from a stationary observer of view ) higher energy emitted opposite to the moving direction than that and thus the particle would be slowed down. In this form, the statement is probably due to incorrect Poyntings derivation (1903), wrong. The correct explanation when viewed from the perspective of a stationary observer, ie an observer who does not move to the sun, is more complicated:

Upon absorption of a photon of momentum of the photon is transmitted to the particles. This pulse has the direction of the photon, that is in a circular arc exactly perpendicular to the moving direction. That is, the impulse of the photon does not change the momentum of the particle in its direction of movement. The photon is, however, not only its momentum, but also its energy to the particle. According to the mass-energy equivalence in special relativity theory by increasing the mass of the particle. Because of the conservation of momentum thereby decreases the velocity of the particle.

The emission of energy as heat radiation in the system of the observer at rest is due to the Doppler effect actually forward emitted more radiation energy and thus more momentum than backwards. Thus, the momentum of the particle is reduced, at the same time decreases because the energy output but also the mass. The velocity of the particle remains unchanged. Meaning, it is also in this reference system to the conclusion that the speed decreases in the absorption of the photon and not the radiation of energy.

Source directory

• John Henry Poynting: Radiation in the Solar System: its Effect on Temperature and its Pressure on Small Bodies (PDF, 3.5 MB). In: Philosophical Transactions of the Royal Society of London, Series A. 202, 1904, pp. 525-552.
• John Henry Poynting: Radiation in the Solar System: its Effect on Temperature and Its Pressure on Small Bodies. In: Monthly Notices of the Royal Astronomical Society. 64, 1903, pp. 265-266. ( Summary of the Philosophical Transactions article. )
• Howard Percy Robertson: Dynamical Effects of Radiation in the Solar System. In: Monthly Notices of the Royal Astronomical Society. 97, 1937, pp. 423-438.
• Eva Ahnert - Rohlfs: radiation pressure, Poynting - Robertson effect and interstellar matter. In: Communications of the Sonneberg Observatory. 29, No. 3/4, 1953, pp. 39-45.