Exhibit Codex
Mercury
A heavily cratered rocky world with an extremely thin exosphere.
Open interactive exhibit ↗About this exhibit
Terrestrial planet
Physical profile · seven measurements
- Mean radius
- 2,439.4 km
- Mass
- 0.330103 ×10²⁴ kg
- Bulk density
- 5.4289 g/cm³
- Sidereal rotation
- 58.6462 Earth days
- Sidereal orbit
- 0.2408467 Earth years
- Equatorial gravity
- 3.7 m/s²
- Escape speed
- 4.25 km/s
Present-day reference values, rounded from JPL Solar System Dynamics. These are not reconstructed ancient measurements. Gas-giant gravity refers to a reference atmospheric level, not solid ground. Sidereal rotation differs from the solar day.
Reference and coverage
Time scaling is shared with the interactive atlas. Surface interpretations and reconstructed history have different levels of certainty.
Planetary record
Rock & metal
Mercury has an unusually large metallic core beneath its rocky exterior. Impact basins and long scarps record collisions and contraction as its interior cooled.
An extreme day
One orbit takes about 88 Earth days. Its 3:2 spin–orbit resonance produces a solar day of about 176 Earth days. Almost no atmosphere moves heat between day and night.
Polar surprises
Permanently shadowed polar craters can preserve water ice despite the intense sunlight elsewhere.
Time in this exhibit
4.6 billion years ago · Cloud & disk
The young Sun is surrounded by a disk of gas and dust. Planet formation is underway.
4.54 billion years ago · Young planets
The terrestrial planets are growing through accretion and impacts. Their orbits and surfaces continue to evolve.
Present · Modern system
Eight planets orbit our Sun. This layout compresses distances and adjusts sizes to make every world accessible.
Read the detailed records
Open the full exhibit Codex for individual structure records and time-specific information. The Credits page lists source creators, licenses and adaptations.