Yarkovsky effect
A tiny thrust on a spinning asteroid caused by it giving off absorbed sunlight as heat in a slightly lopsided direction.
A rotating asteroid absorbs sunlight on its day side but re-radiates that energy as infrared only after a delay, because the surface takes time to heat and cool. The warmest region therefore lies on the 'afternoon' side, and the infrared photons leaving it carry momentum, producing a minute, persistent force. For prograde rotators this diurnal Yarkovsky effect increases the semi-major axis; retrograde rotators spiral inward. A weaker seasonal component also exists. The idea goes back to the engineer Ivan Yarkovsky around 1900, and its torque-producing cousin, which alters spin rate and axis tilt, is known as the YORP effect.
The force is tiny but measurable. It was first detected in 2003 for the near-Earth asteroid 6489 Golevka by radar ranging, and OSIRIS-REx tracking showed Bennu's orbit drifting by roughly 280 metres a year, an essential term in Bennu's impact-risk assessment.
For meteoritics, Yarkovsky drift explains how collisional fragments, metres to kilometres across, migrate slowly across the belt into resonances such as the 3:1 and ν6, which then deliver them to Earth-crossing orbits. This steady supply also helps explain why cosmic-ray exposure ages of stony meteorites are mostly millions to tens of millions of years rather than short. It is inferred from precise orbit tracking, never seen directly.
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