Here's why:
* Kepler's Laws of Planetary Motion: Johannes Kepler's laws of planetary motion explain this. The third law states that the square of a planet's orbital period (the time it takes to complete one orbit) is proportional to the cube of the semi-major axis of its orbit (the average distance from the sun).
* Gravity and Velocity: The closer a planet is to the sun, the stronger the gravitational pull. To counteract this strong pull and stay in orbit, the planet needs to travel at a higher speed. Imagine a ball on a string. The faster you swing it, the tighter the circle it makes.
* Example: Mercury, the closest planet to the sun, has a much shorter orbital period than Earth, meaning it travels much faster around the sun.
So, the closer a planet is to the sun, the faster it travels in its orbit!
