The planet nearest to the sun is Mercury.

Explanation:
Mercury is the closest planet to the Sun in our solar system. It is named after the Roman messenger god, Mercury, who was known for his speed. Here are some key points to understand why Mercury is the closest planet to the Sun:

1. Average Distance from the Sun:
- Mercury has an average distance of about 36 million miles (58 million kilometers) from the Sun.
- This distance is significantly closer compared to other planets in our solar system.

2. Orbit and Revolution:
- Mercury has an elliptical orbit around the Sun, which means its distance from the Sun varies throughout its orbit.
- Its closest approach to the Sun, called perihelion, is about 29 million miles (47 million kilometers), while its farthest point, called aphelion, is around 43 million miles (70 million kilometers).

3. Size and Mass:
- Mercury is the smallest planet in our solar system, with a diameter of about 3,032 miles (4,879 kilometers).
- It has only about 38% the gravity of Earth, making it much less massive.

4. Temperature Extremes:
- Due to its proximity to the Sun, Mercury experiences extreme temperature variations.
- During the day, the surface temperature can reach up to 800 degrees Fahrenheit (430 degrees Celsius), while at night, it can drop to around -290 degrees Fahrenheit (-180 degrees Celsius).

5. Exploration:
- Mercury has been visited by a few spacecraft missions, including NASA's Mariner 10 in the 1970s and MESSENGER (MErcury Surface, Space ENvironment, GEochemistry, and Ranging) in the 2000s.
- These missions have provided valuable data and images, helping scientists better understand the planet's composition, geology, and magnetic field.

In conclusion, Mercury is the planet closest to the Sun in our solar system. Its small size, short distance from the Sun, and extreme temperature variations make it a fascinating celestial body to study.