The closest planet to the Sun is Mercury. It orbits at an average distance of about 36 million miles (58 million kilometers), or 0.387 astronomical units (AU), from the Sun

. Mercury is also the smallest planet in the solar system, slightly larger than Earth's Moon

. It completes an orbit around the Sun every 88 Earth days, making it the fastest orbiting planet

. Mercury has a very eccentric (non-circular) orbit, ranging from about 46 million km at its closest point to nearly 70 million km at its farthest from the Sun

. Despite being closest to the Sun, Mercury is not the hottest planet; Venus holds that distinction due to its thick greenhouse gas atmosphere

. In summary:

• Closest planet to the Sun: Mercury
• Average distance: ~36 million miles (58 million km)
• Orbit period: 88 Earth days
• Size: Smallest planet, just larger than Earth's Moon
• Temperature extremes: Very hot on the sunlit side and extremely cold on the dark side due to lack of atmosphere

This makes Mercury the Sun’s nearest planetary neighbor