Mercury

**Mercury** (Mercury) is the smallest planet, and 2nd densest planet in the Sol system and the one closest to Sol, with an orbital period of about 88 Terra days. It has no natural satellites and it's surface temperature is the most varied in the system. With little atmosphere, temperature ranges from 100 K (−173 °C; −280 °F) in the night to 700 K (427 °C; 800 °F) in the day. The only surface region habitable for humans are the poles, which are always below (−93 °C; −136 °F). Mercury also has the least axial tilt of any planet in the Sol system, due to its proximity to Sol. Mercury's surface is heavily cratered and resembles Terra's Luna. Among the system, Mercury's rotation is unique. It is named after the Roman god of speed and messengers, due to its orbital speed.

## Composition

Mercury's interior consists of about 70% metallic and 30% silicate materials. Mercury's density is the second highest in the Sol System at 5.427 g/cm^3, only slightly less than Terra's density of 5.515 g/cm^3. If the effect of gravitational compression were to be factored out, the materials of which Mercury is made would be denser, with an uncompressed density of 5.3 g/cm^3 versus Earth's 4.4 g/cm^3. Mercury's core occupies about 42% of its volume; for Terra this proportion is 17%. Mercury has a molten core. Surrounding the core is a 650 km mantle consisting of silicates. Mercury's crust is over 100 km thick.

Mercury's core has a higher iron content than that of any other major planet in the Sol System. Scientists hypothesize that Mercury originally had a metal–silicate ratio similiar to chondrite asteroids and a mass approximately 2.25 times its current mass. Early in the Sol system's history, Mercury may have been struck by an object of approximately 1/6th that mass and several thousand kilometers across. The impact would have stripped away much of the original crust and mantle, leaving the core behind as a relatively major component. A similiar event probably happened to Terra, forming Luna.

### Surface

Mercury's surface is similar in appearance to that of Luna, showing extensive plains and heavy cratering. One unusual feature of Mercury's surface is the numerous compression folds that crisscross the plains. The folds can be seen on top of other features, such as craters and smoother plains. Mercury's surface is flexed by significant tidal bulges raised by Sol.. Sol's tides on Mercury are about 17 times stronger than Luna's on Terra.

#### Conditions

The surface temperature of Mercury ranges from -173°C to 427°C at the most extreme places and during opposing times. Although the daylight temperature at the surface of Mercury is generally extremely high, frozen water exists on Mercury. The floors of deep craters at the poles are never exposed to direct sunlight, and temperatures there remain below 102 K; far lower than the global average. The icy regions contain about 1015 kg of ice, and is covered by a layer of regolith that inhibits sublimation. By comparison, the Antarctic ice sheet on Terra has a mass of about 4×10^18 kg, and Mars's south polar cap contains about 1016 kg of water, right before terraforming. Mercury is too small and hot for its gravity to retain any significant atmosphere over long periods of time, especially as close as it is to Sol.

## Dynamics

### Magnetosphere

Despite its small size and slow 59-day-long rotation, Mercury has a significant, and global, magnetic field. This magnetic field is generated by a dynamo effect, in a manner similar to the magnetic field of Terra. This dynamo effect would result from the circulation of the planet's iron-rich liquid core. Particularly strong tidal effects caused by the planet's high orbital eccentricity would serve to keep the core in the liquid state necessary for this dynamo effect. Mercury's magnetic field is strong enough to deflect the solar wind and cosmic rays around the planet, creating a magnetosphere.

## Orbit and rotation

Mercury has the second most eccentric orbit of all the planets; its eccentricity is 0.21 with its distance from Sol ranging from 0.307 to 0.468 AU. It takes 87.969 Terran days to complete an orbit. Mercury's axial tilt is almost zero, with the best measured value as low as 0.027 degrees. This is significantly smaller than that of Jupiter, which has the second smallest axial tilt of all planets at 3.1 degrees. This means that to an observer at Mercury's poles, the center of Sol never rises more than 2.1 arcminutes above the horizon.

Due to the rotation of Mercury, its short orbital period, and its orbital eccentricity, days on Mercury are unique. At certain points on Mercury's surface, an observer would be able to see Sol rise about halfway, then reverse and set before rising again, all within the same Mercurian day. In addition to this, the apparent Mercurian day, the day to an observer on Mercury, is actually 176 days.

## Civilization

### History

#### Initial settlement

As part of the human home star system, Mercury serves an important role. However, due to the Delta-V required to reach the surface of Mercury, or even enter orbit, it is costlier to get to the planet itself. In addition to this, temperature fluctuations on the planet are hazardous on periods of weeks. The colonization of Mercury began in 2059 CE as part of the Egeria program. However, the designs of the project had to overcome several issues.

Due to strange and unique rotation and its proximity to Sol, initial colonization was semi-difficult. A small fraction of the planet's surface is habitable, about 15%. Even though proximity to Sol brought problems such as temperature, this proximity also brought 6.68 times the amount of solar energy received on Terra. This allowed for widespread use of virtually unlimited power supplied by Sol. An artificial magnetosphere was not needed for this colony, as Mercury provides itself one, and colonies would be placed underground regardless, to avoid temperature hazards. Humans first deployed the setup for the human colony near the poles by 2059 CE. Following the arrival of the first robots, supplies, and construction material, 50 humans soon followed. These underground habitats were built on a rotating base, providing roughly 0.7 g, enough gravity that the average Mercurian colonist could return to Terra instantly with no uncomfort.

Quickly establishing underground habitats and aided by robots, the first settlement on Mercury was established. The first farms took advantage of the long Mercurian day in addition with LED light. Most water required for the colonists and farms were taken from the Mercurian ice caps and purified. The underground colony became self-sustaining by 2081 CE due to the artificial farms. The first animals for consumption arrived on Mercury from Terra by 2083 CE and animal transportation ended by 2094 CE.

### Economy and human geography

Due to receiving six times the amount of solar power Terra gets, almost all power on this planet is solar power. However, the night requires battery or another sources of power. The gravity of 38% of Terra's is tolerable by inhabitants of Mercury and requires daily exercise to keep Terran health standards. Because of this, fitness is high and obesity low.

Mercury's proximity to Sol has implications to its economy, human geography, and importance. The fuel required to reach Mercury is the highest in the system, so trade stops by Venus or Terra first. Mercury also serves an high importance in the safety of the system. The planet serves as a major station for monitoring Sol, especially for geomagnetic storms, solar wind, flares, or coronal mass ejections.

Other than monitoring Sol, the other focus of this planet's economy is based around antimatter production. The first production of antimatter on Mercury occurred on 2098 CE, following the construction of the first antimatter factory. Due to the danger of these operations, they occur thousands of miles away from any settlements, far underground, and under extremely powerful antimatter traps. Mercury-produced antimatter is most often used for the initiation of fusion reactors or fuel. Less often, it is used for medical scans or treatment, and on occasion, antimatter bombs.