When space probe Voyager 2 passed by Saturn, its speed increased (but not due to firing its engines). What must have happened?
A) Saturn must have lost a very tiny bit of its orbital energy.
B) Voyager 2 must have dipped through Saturn's atmosphere.
C) Saturn's rotation must have sped up slightly.
D) Saturn must have captured an asteroid at precisely the moment that Voyager 2 passed by.

Question

Quizplus · Accepted Answer

By the principle of conservation of energy, if the speed of an object (in this case, Voyager 2) increases, it must have gained some energy. In this case, that energy must have come from somewhere, and it's likely that Saturn lost a very tiny bit of its orbital energy due to the gravitational interaction with the passing Voyager 2. This is called a gravitational assist or slingshot maneuver, which is commonly used by spacecraft to increase or decrease their speed without using fuel.

When Space Probe Voyager 2 Passed by Saturn, Its Speed