Here's why:
* Mass Difference: Saturn is vastly more massive than the Cassini spacecraft. The ratio is roughly 10^20 to 1 (Saturn is 100 billion billion times more massive). This means Cassini's gravitational influence on Saturn is negligible.
* Orbital Mechanics: The process of entering orbit is carefully calculated to ensure the spacecraft's gravitational pull doesn't disrupt the planet's existing motion. Cassini was designed to be a passive observer, not a perturbing force.
* Long-Term Effects: While the spacecraft's gravitational pull on Saturn is minuscule, over very long periods of time, a small, cumulative effect could theoretically occur. However, these effects are insignificant compared to the natural variations in Saturn's orbital parameters and would be impossible to measure.
In essence, the effect of Cassini on Saturn's orbit was akin to a fly landing on a cruise ship. The fly might feel a slight jolt, but the ship's course remains unchanged.
