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Ownership: UCP
System: Sol system, inmost planet
Type: Geo-morteus iron world
Location: Alpha Quadrant

Mercury is the closest planet to Sol, and the second-smallest planet in the Sol system. It has no natural satellites and no atmosphere. The planet has a large iron core which generates a faint magnetic field. Surface temperatures on Mercury range from about 90-700 K, with the subsolar point being the hottest and the bottoms of craters near the poles being the coldest.

Planetary statistics

Equatorial Radius: 2 439.7 km
Diameter: 4 880 km
Mass: 3.3022 x 10^23 kg
Density: 5.427 g/cm^3
Escape Velocity: 4.25 x 10^3 m/s

Orbital parameters

Average orbit distance: 57 909 175 km (0.387099 au)
Length of day: 58.646 days
Length of year: 87.96925 days
Mean Orbit Velocity: 47.873 km/s
Equatorial Inclination to Orbit: 0 degrees
Eccentricity: 0.205629
Orbital inclination: 7°00'18"
Longitude of the ascending node: 48°18°'05"
Argument of pericentre: 29°07'07"
Mean anomaly: 74°25'34"

Environmental properties

Atmosphere: Tenuous

Min./Max. Surface Temperature: -173/427 °C.
Surface Gravity: 0.3865 G


Natural resources: Magnesium, sulphur

Industry: Mercury produces incinerator beams, torpedoes, shields, sensors, engines and jump drives.

Surface features

During and shortly following the formation of Mercury, it was heavily bombarded by comets and asteroids for a period that came to an end 3.8 billion years ago. During this period of intense crater formation, the surface received impacts over its entire surface, facilitated by the lack of any atmosphere to slow impactors down. During this time, the planet was volcanically active; basins such as the Caloris Basin were filled by magma from within the planet, which produced smooth plains.

Apart from craters with diameters in the range of hundreds of meters to hundreds of kilometers, there are others of gigantic proportions such as Caloris, the largest structure on the surface of Mercury with a diameter of 1,300 km. The impact was so powerful that it caused lava eruptions from the crust of the planet and left a concentric ring over 2 km tall surrounding the impact crater. The consequences of Caloris are also impressive; it is widely accepted as the cause for the fractures and leaks on the opposite side of the planet.

The plains of Mercury have two distinct ages: the younger plains are less heavily cratered and probably formed when lava flows buried earlier terrain. One unusual feature of the planet's surface is the numerous compression folds which criss-cross the plains. It is thought that as the planet's interior cooled it contracted, and its surface began to deform. The folds can be seen on top of other features, such as craters and smoother plains, indicating that they are more recent. Mercury's surface is also flexed by significant tidal bulges raised by Sol.

At certain points on Mercury's surface, an observer would be able to see the sun rise about halfway, then reverse and set before rising again, all within the same Mercurian day. This is because approximately four days prior to perihelion, Mercury's orbital velocity exactly equals its rotational velocity so that Sol's apparent motion ceases; at perihelion, Mercury's orbital velocity then exceeds the rotational velocity. Thus, Sol appears to be retrograde. Four days after perihelion, Sol's normal apparent motion resumes.

Mercury's axial tilt is only 0.01 degrees. This means an observer at Mercury's equator never sees the central sun more than 1/100 of one degree north or south of the zenith.

Interior composition

Mercury has a relatively large iron core. Mercury's composition is approximately 70% metallic and 30% silicate. The average density is 5430 kg/m³. The iron core fills 42% of the planet's volume.

Surrounding the core is a 600 km mantle. It is thought that early in Mercury's history, a giant impact with a body several hundred kilometres across stripped the planet of much of its original mantle material, resulting in the relatively thin mantle compared to the sizable core.


Despite its slow rotation, Mercury has a relatively strong magnetosphere. It is possible that this magnetic field is generated by a dynamo of circulating liquid core material. However, scientists are unsure whether Mercury's core could still be liquid, although it could perhaps be kept liquid by tidal effects during periods of high orbital eccentricity. It is also possible that Mercury's magnetic field is a remnant of an earlier dynamo effect that has now ceased, with the magnetic field becoming "frozen" in solidified magnetic materials.

Iron content

Mercury has a higher iron content than any other object in the Sol system. Several theories have been proposed to explain Mercury's high metallicity. One theory is that Mercury originally had a metal-silicate ratio similar to common chondrite meteors and a mass approximately 2.25 times its current mass, but that early in the solar system's history Mercury was struck by a planetesimal of approximately 1/6 that mass. The impact would have stripped away much of the original crust and mantle, leaving the core behind.

Alternatively, Mercury may have formed from the solar nebula before the star's energy output had stabilized. The planet would initially have had twice its present mass, but as the protosun contracted, temperatures near Mercury could have been between 2500–3500 K; and possibly even as high as 10000 K. Much of Mercury's surface rock would have vaporized at such temperatures, forming an atmosphere of "rock vapor" which would have been carried away by the solar wind.

A third theory suggests that the solar nebula caused drag on the particles from which Mercury was accreting, which meant that lighter particles were lost from the accreting material. Each of these theories predicts a different surface composition. Tentative suggestions have been made that Mercury may be a Chthonian planet.

See also