Planet

Mercury

Terrestrial planet · A small world of great contrasts

The smallest planet and the closest to the Sun. Its cratered surface preserves the traces of ancient impacts.

Prepare an observation This stop on the Solar System trail

Schematic illustration: Mercury — Educational illustration · shapes and sizes are not to scale.

Equatorial diameter: 4 879 km
Mean orbital distance: 57,9 million km
Orbital period around the Sun: 88 days

What makes this world interesting

Its very tenuous exosphere retains little heat: the differences between day and night are extreme. Despite its proximity to the Sun, Mercury is cooler than Venus.

Observe or explore it

Look low in the sky at dusk or dawn, depending on its elongation. Wait until the Sun is below the horizon before pointing an instrument.

Connect the discoveries

The Sun Venus

Sources and reference information

NASA Science — Mercury · NASA/NSSDCA — planetary data

Rounded educational data, sources consulted on 18 October 2026. Orbital distances are mean reference distances from the Sun, not current distances from Earth. Periods are expressed in Earth time. The planner provides date-specific positions for supported targets.

Understand its motion. Explore a simplified orbit in the laboratory →