Final answer:
The brightness of the Sun on Mars is about half as bright as its brightness on Earth.
Step-by-step explanation:
The brightness of the Sun on Mars compared with its brightness on Earth can be determined by considering the inverse square law of brightness. The amount of starlight received per unit area of a planet's surface decreases with the square of the distance from the star. Mars is about 1.52 AU away from the Sun, which means it receives approximately 1/(1.52)² = 0.43 (about half) as much light per square meter of planet surface as Earth does.