📖 About Mercury

Mercury is the smallest planet in our solar system and the closest to the Sun, orbiting at an average distance of just 57.9 million km. With a diameter of 4,880 km, it is only slightly larger than Earth’s Moon. Mercury has virtually no atmosphere—just an ultra-thin exosphere of atoms blasted off the surface by solar wind and micrometeorites.

Mercury holds the record for the most extreme temperature swings in the solar system: dayside temperatures soar to 427°C while the nightside plummets to -173°C—a range of 600 degrees. Remarkably, Mercury’s day (one sunrise to the next) takes 176 Earth days, while its year is only 88 Earth days—making a single day on Mercury longer than two Mercurian years. The planet’s oversized iron core, comprising about 85% of its radius, is the proportionally largest of any planet.

ESA and JAXA’s joint BepiColombo mission has been performing Mercury flybys since 2021 and will enter orbit in 2026. Its two orbiters will study Mercury’s magnetic field, surface composition, and the mysterious permanently shadowed polar craters where water ice has been confirmed by radar. NASA’s MESSENGER mission (2011-2015) previously mapped the entire surface and discovered that Mercury has been geologically active more recently than expected.

🔭 Key Features

🔬 Science & Future

Mercury’s oversized iron core remains one of the great puzzles of planetary science. Theories include a giant impact that stripped the original mantle, or solar wind erosion of a once-larger planet during the early solar system. BepiColombo’s measurements of Mercury’s gravity field and surface composition will help resolve this mystery and reveal how terrestrial planets form.

The discovery of water ice at Mercury’s poles—on the closest planet to the Sun—was one of the most surprising findings in planetary science. Understanding how this ice survived billions of years provides insights into water delivery throughout the inner solar system. Mercury also serves as a unique testbed for general relativity, as its orbit was the first confirmation of Einstein’s predictions.

📜 Discovery & Exploration

Mercury has been observed since at least the 3rd millennium BCE by the Sumerians. Ancient Greeks gave it two names—Apollo (morning star) and Hermes (evening star)—before realizing it was one object. Due to its proximity to the Sun, Mercury is notoriously difficult to observe from Earth and can only be seen near sunrise or sunset.

NASA’s Mariner 10 was the first spacecraft to visit Mercury, making three flybys in 1974-1975 and mapping about 45% of the surface. The MESSENGER spacecraft orbited Mercury from 2011 to 2015, mapping the entire surface and making groundbreaking discoveries including polar ice and recent volcanic activity. BepiColombo will build on this legacy starting in 2026.