Here's why:
* Potential Energy and Gravity: Potential energy in the context of a comet's orbit is related to its position within the Sun's gravitational field. The farther away an object is from the Sun, the weaker the Sun's gravitational pull and the higher its potential energy.
* Orbital Mechanics: As a comet moves closer to the Sun (perihelion), its kinetic energy increases (it speeds up) and its potential energy decreases. Conversely, as it moves away from the Sun (aphelion), its kinetic energy decreases (it slows down) and its potential energy increases.
Important Note: While a comet has the greatest potential energy at aphelion, its total mechanical energy (potential energy + kinetic energy) remains constant throughout its orbit. This is a consequence of the conservation of energy in a closed system.