Mercury is the innermost planet and the smallest major planet in the Solar System. Its statistics combine current reference values, geological estimates, model parameters and mission measurements, so each figure below identifies its period, geography and measurement type.
Key Mercury Statistics
The most broadly useful Mercury statistics are:
- 0.33010 × 10^24 kg is Mercury’s mass in the current planetary fact-sheet reference for Mercury.
- 2,439.7 km is Mercury’s volumetric mean radius in the current planetary fact-sheet reference.
- 5,429 kg/m³ is Mercury’s mean density in the current planetary fact-sheet reference.
- 87.969 days is Mercury’s sidereal orbital period in the current orbital-elements reference for Mercury.
- 46.000 million km is Mercury’s perihelion distance in the current orbital-elements reference for its orbit around the Sun.
- 69.818 million km is Mercury’s aphelion distance in the current orbital-elements reference for its orbit around the Sun.
- 1,407.6 hours is Mercury’s sidereal rotation period in the current planetary fact-sheet reference.
- 4,222.6 hours is Mercury’s solar day in the current planetary fact-sheet reference.
- 430°C is Mercury’s cited daytime surface maximum in NASA’s fact-page reference for sunlit Mercury.
- −180°C is Mercury’s cited nighttime surface minimum in NASA’s fact-page reference for the night side.
- 1,550 km is the diameter of the Caloris impact basin in the geological feature measurement cited by NASA.
- About 2,074 km is Mercury’s estimated metallic-core radius in NASA’s fact-page reference.
- Below approximately 10,000 kg is Mercury’s estimated exosphere mass in the current planetary fact-sheet reference.
- 0.0025–0.007 Gauss is the modeled surface magnetic-field strength in the MESSENGER Model 2010 reference.
- Nearly 100,000 surface images were produced during MESSENGER’s primary mission from 2011-03-18 to 2012-03-17.
- About 25 km was MESSENGER’s orbital altitude on 2014-09-12, shortly before its final phase.
- About 14,080 km/h was MESSENGER’s impact speed at Mercury on 2015-04-30.
Contents
- Mercury size, mass and density statistics
- Mercury orbit and solar-distance data
- Mercury surface, temperature and ice context
- Mercury interior, geology and long-term trends
- Mercury exosphere and magnetic-field measurements
- Mercury exploration statistics
Mercury Size, Mass and Density Statistics
NASA’s Mercury Fact Sheet gives the following current planetary reference values. These are properties of Mercury itself, not population estimates or forecasts.
| Measure | Mercury value | Scope |
|---|---|---|
| Mass | 0.33010 × 10^24 kg | Current fact-sheet value |
| Volume | 6.083 × 10^10 km³ | Current fact-sheet value |
| Equatorial radius | 2,440.5 km | Reference geophysical parameter |
| Polar radius | 2,438.3 km | Reference geophysical parameter |
| Volumetric mean radius | 2,439.7 km | Reference geophysical parameter |
| Mean density | 5,429 kg/m³ | Reference bulk density |
| Mean surface gravity | 3.70 m/s² | Mean value |
| Escape velocity | 4.3 km/s | Reference value |
Source: Mercury Fact Sheet.
For the fact-sheet comparison with Earth, Mercury’s mass is 5.53% of Earth’s mass, its volume is 5.62% of Earth’s volume, and its mean density is 98.5% of Earth’s mean density. These displayed ratios are source comparisons rather than new calculations.
The same current fact-sheet summary gives Mercury a 7 km topographic range. That is a global summary of elevation variation, not a measurement of one named landform.
Mercury Orbit, Rotation and Solar-Distance Data
Mercury’s orbit is compact, fast and noticeably eccentric. The current orbital-elements reference places its semimajor axis at 57.909 million km, with a perihelion of 46.000 million km and an aphelion of 69.818 million km.
| Orbital or rotational measure | Value | Definition or period |
|---|---|---|
| Sidereal orbital period | 87.969 days | Current orbital elements |
| Tropical orbital period | 87.968 days | Current orbital elements |
| Synodic period | 115.88 days | Mercury as seen from Earth |
| Mean orbital velocity | 47.36 km/s | Current orbital elements |
| Maximum orbital velocity | 58.97 km/s | Orbital maximum |
| Minimum orbital velocity | 38.86 km/s | Orbital minimum |
| Orbital inclination | 7.004° | J2000 reference epoch |
| Orbital eccentricity | 0.2056 | J2000 reference element |
Source: Mercury Fact Sheet.
Mercury’s sidereal rotation period is 1,407.6 hours, while one solar day lasts 4,222.6 hours. Its obliquity is 0.034°, the axial tilt relative to its orbit in the current planetary fact-sheet reference.
At Mercury’s average solar distance, sunlight takes 3.2 minutes to arrive. NASA identifies this as an average-distance figure, so it should not be treated as the travel time at either perihelion or aphelion; the source is Mercury: Facts.
Mercury Surface, Temperature and Ice Context
NASA’s cited surface extremes show why Mercury’s environment cannot be summarized by one average temperature. The sunlit surface can reach 430°C, while the nighttime surface can fall to −180°C, a cited day-night span of about 610°C between those extremes.
| Surface feature or condition | Quantified statistic | Scope |
|---|---|---|
| Daytime surface maximum | 430°C | Sunlit Mercury surface |
| Nighttime surface minimum | −180°C | Night-side Mercury surface |
| Caloris impact basin | About 1,550 km diameter | Named surface basin |
| Rachmaninoff basin | About 306 km diameter | Named surface basin |
| Large cliffs | Up to about 1 mile high | Representative large cliffs |
Source: Mercury: Facts.
The Caloris basin is about 1,550 km across, compared with about 306 km for the Rachmaninoff basin. NASA also describes Mercury’s cliffs as extending hundreds of miles and rising up to about 1 mile, but that description applies to representative large cliffs rather than every cliff.
Qualitative observations about polar ice are not assigned a numerical inventory here. The available quantified record supports temperature, basin and cliff measurements, while local polar conditions and surface-bounded processes require their own definitions and observation contexts.
Mercury Interior, Geology and Long-Term Trends
NASA estimates Mercury’s metallic core radius at about 2,074 km, or about 85% of the planet’s radius. The outer shell, including mantle and crust in the cited description, is about 400 km thick; both figures are approximate structural estimates rather than direct census-style measurements.
Older and newer interior estimates should be kept separate. The peer-reviewed MESSENGER synthesis reports that pre-MESSENGER Mariner 10 estimates placed the core radius between 72% and 90% of Mercury’s planetary radius, while the same synthesis compares Earth’s metallic core radius at about 55% of planetary radius.
The geological record also measures change over deep time:
- Mariner 10 flybys in 1974–1975 covered about 45% of Mercury’s surface, so the result was not a global map.
- Long lobate scarps imply estimated global contraction of 1–2 km over the past 4 billion years, a geological inference rather than a continuously observed trend.
- The peer-reviewed MESSENGER synthesis describes about 1 billion years of voluminous volcanism after Mercury’s early magma-ocean history, an inferred duration based on mission data and modeling.
Sources: A whole new Mercury: MESSENGER reveals a dynamic planet at the last frontier of the inner solar system and Mercury: Facts.
Mercury Exosphere and Magnetic-Field Measurements
Mercury has an extremely tenuous, variable exosphere rather than a dense atmosphere. The current fact sheet reports its surface pressure as below approximately 5 × 10^-15 bar and its total mass as below approximately 10,000 kg; both are upper limits.
| Exosphere measure | Value | Qualification |
|---|---|---|
| Average temperature | 440 K | Highly variable surface-bounded exosphere |
| Sunward-side temperature | 590–725 K | Varies by local time and location |
| Sodium column abundance | 12,000–200,000 × 10^6 cm^-2 | Range varies with local time or location |
| Magnesium column abundance | 100,000 × 10^6 cm^-2 | Fact-sheet column abundance |
| Oxygen column abundance | Below 40,000 × 10^6 cm^-2 | Upper limit |
| Hydrogen column abundance | 5,000 × 10^6 cm^-2 | Fact-sheet column abundance |
| Potassium column abundance | 800–1,300 × 10^6 cm^-2 | Range varies with local time or location |
Source: Mercury Fact Sheet.
The MESSENGER Model 2010 gives a modeled dipole field strength of 0.002 Gauss-Rh³, with Rh defined as the 2,440-km model radius, and a modeled dipole offset of 0.17 planetary radii. At one planetary radius, the modeled surface field is 0.0025–0.007 Gauss.
NASA describes Mercury’s surface magnetic field as about 1% as strong as Earth’s. That is a rounded estimate and comparison, not a replacement for the model range; both are retained because they describe different levels of precision.
See Mercury: Facts and the Mercury Fact Sheet.
Mercury Exploration Statistics from Mariner 10 and MESSENGER
Mariner 10’s three flybys in 1974–1975 produced about 45% surface coverage, an important early measurement with incomplete global geography. MESSENGER later supplied orbital observations and a much larger image record.
| Mission milestone | Statistic | Measurement period |
|---|---|---|
| Initial MESSENGER orbit | Approximately 9,300 × 200 km; 12-hour period | Initial orbital operations, 2011 |
| Primary-mission surface images | Nearly 100,000 | 2011-03-18 to 2012-03-17 |
| Orbital photograph milestone | 100,000th photograph | Early May 2012 |
| Orbital image milestone | 200,000th image | 2014-02-06 |
| Low orbit | About 25 km altitude | 2014-09-12 |
| Mercury impact | About 14,080 km/h | 2015-04-30 |
Source: MESSENGER – NASA Science.
MESSENGER’s initial Mercury orbit was approximately 9,300 × 200 km with a 12-hour orbital period. During its primary yearlong mission from 2011-03-18 to 2012-03-17, it produced nearly 100,000 surface images.
The mission reached its 100,000th orbital photograph by early May 2012 and its 200,000th orbital image by 2014-02-06. These are separate NASA milestones, so the later count should not be added to the primary-mission rounded total as though they described identical intervals.
The orbit descended to about 25 km on 2014-09-12. MESSENGER then impacted Mercury at about 14,080 km/h on 2015-04-30; the impact location was estimated near 54.4°N, 149.9°W, with NASA noting that the coordinates were probably close to those values.