Closest planet to sun
Pro Research Analysisby 
Searched over 200M research papers
Closest Planet to the Sun: Mercury
Introduction to Terrestrial Planets
The four planets closest to the Sun—Mercury, Venus, Earth, and Mars—are known as the terrestrial planets due to their rocky compositions and proximity to the Sun 23. These planets share many similarities, such as solid surfaces and relatively small sizes compared to the gas giants further out in the Solar System.
Mercury: The Nearest Planet to the Sun
Orbital Characteristics
Mercury is the closest planet to the Sun, orbiting at an average distance of about 0.39 astronomical units (AU) . This proximity results in a very short orbital period; Mercury completes one orbit around the Sun in just 88 Earth days. Its close distance to the Sun also means that it experiences extreme temperature variations, with surface temperatures ranging from -173°C at night to 427°C during the day.
Physical Properties
Mercury is the smallest of the terrestrial planets, with a diameter of about 4,880 kilometers. Despite its small size, it has a relatively high density, indicating a large metallic core. This core is believed to make up about 85% of the planet's radius, contributing to its significant magnetic field, which is about 1% as strong as Earth's.
Proxima Centauri and Nearby Exoplanets
Proxima b: An Earth-Mass Planet
While Mercury is the closest planet to the Sun within our Solar System, the closest known exoplanet to the Sun is Proxima b, which orbits the star Proxima Centauri 147. Proxima Centauri is the nearest star to the Sun, located about 4.24 light-years away. Proxima b is an Earth-mass planet with a minimum mass of 1.3 Earth masses and orbits its star at a distance of approximately 0.05 AU, completing an orbit in about 11.2 days 14.
Potential for Habitability
Proxima b lies within the habitable zone of Proxima Centauri, where conditions might allow for liquid water to exist on its surface 14. However, the planet is subject to high levels of X-ray radiation from its host star, which could affect its atmosphere and potential habitability .
Conclusion
Mercury holds the title of the closest planet to the Sun within our Solar System, characterized by its rapid orbit and extreme temperature fluctuations. Beyond our Solar System, Proxima b is the nearest known exoplanet, orbiting the star Proxima Centauri. While Mercury and Proxima b are vastly different in terms of their environments and potential for life, both offer valuable insights into planetary science and the conditions that can exist in close proximity to a star.
Sources and full results
Most relevant research papers on this topic