What is the closest planet to our solar system's sun?

The closest planet to our solar system's sun is Mercury. Mercury is the nearest planet to the sun due to its orbit, which lies closest to the sun compared to all other planets in the solar system. Its close proximity to the sun means that it experiences extremely high temperatures, inhospitable conditions, and a lack of atmosphere, making it inhospitable for life as we know it. Overall, the combination of its orbit and proximity to the sun makes Mercury the closest planet to our solar system's sun.