In addition, the force of light acting on an object is called radiant pressure. The pressure of solar radiation can blow something out of the solar system and can also cause something to fall on the sun. Let's study a particle near the sun. The particle is subjected to solar radiation pressure proportional to the cross-sectional area of the particle. The gravity acting on a particle is proportional to its mass, and its mass is proportional to its volume. If the linearity of the particle is X, its cross-sectional area is proportional to X^2, and its volume is proportional to X^3; then as long as the particle is small enough, the ratio of X^2 and X^3 can be arbitrarily large. When X=1 unit, X^2=1 unit^2, X^3=1 unit^3; and when X=0.1 unit, X2=0.01 unit^2, X3=0.001 unit^3. So when X is small enough, the pressure of solar radiation can exceed gravity, which is why the comet's tail always faces away from the sun.
Assuming that gravity is greater than the pressure of radiation, the particles are bound in the solar system. When the particles move around the sun, the sunlight shines on the particles like rain. (If the orbit is round, the direction of sunlight is perpendicular to the direction of particle movement). But from a particle point of view, for a moving particle, the sun's rays are radiated from the front (astronomers call it optical aberration). Therefore, the radiation pressure has a component opposite to the direction of particle orbital motion. Although the effect is small, it continues, and the particle's orbital motion speed decreases, causing it to fall spirally onto the sun. This is the Poynyan-Robertson effect. And it acts as a vacuum cleaner in the solar system. This makes the mass of the solar system certain, and will not decrease or increase.
