Mercury

Mercury

Geography

Mercury's surface is similar in appearance to that of Luna, showing extensive mare-like plains and heavy cratering, indicating that it has been geologically inactive for billions of years. Albedo features are areas of markedly different reflectivity, which include impact craters, the resulting ejecta, and ray systems. Larger albedo features correspond to higher reflectivity plains. 
Craters on Mercury range in diameter from small bowl-shaped cavities to multi-ringed impact basins hundreds of kilometers across. They appear in all states of degradation, from relatively fresh rayed craters to highly degraded crater remnants. Mercurian craters differ subtly from lunar craters in that the area blanketed by their ejecta is much smaller, a consequence of Mercury's stronger surface gravity. During the time Mercury was under heavy bombardment it was volcanically active; basins were filled by magma, producing smooth plains similar to the maria found on Luna. One of the most unusual craters is Apollodorus, or "the Spider", which hosts a serious of radiating troughs extending outwards from its impact site.
The largest known crater is Caloris Planitia, or Caloris Basin, with a diameter of 1,550 km. The impact that created the Caloris Basin was so powerful that it caused lava eruptions and left a concentric mountainous ring 2 km tall surrounding the impact crater. The floor of the Caloris Basin is filled by a geologically distinct flat plain, broken up by ridges and fractures in a roughly polygonal pattern. This same impact is likely responsible for the rotational "stalling" that resulted in Mercury's abnormal orbit.

Climate

Mercury's climate is defined by its extremes. Similar to how moons orbit their host planet, Mercury's rotation is tidally locked with the sun. Anybody unlucky enough to be living on the equator would have to endure almost 60 consecutive days of direct sunlight every Mercurian year. Mercury's seasons are equally extreme due to the planet's orbital eccentricity. Mercury's distance from the sun varies by up to 33% over the course of a year. At its closest the Sun appears more than four times as large as it does from the Earth's surface.
Such conditions are far too hostile for life to live comfortable and Mercurians must find refuge from the extremes at the poles. Living near the north or south pole makes the Mercurian day shrink from two months to more tolerable lengths, and with it the temperature falls within a reasonable domain. Distance from the equator doesn't get you any further from the Sun, however, and Mercurian summers are still scaldingly hot.

History

With such close proximity to the Sun, it was long thought impossible to terraform Mercury even with the most advanced technological and thaumaturgical methods. Any artificial atmosphere or magnetosphere would be stripped away by unrelenting solar wind before any habitable conditions could form. However one unique feature of Mercury's geology would prove to be the key to terraforming Planet Number One.
Like most hostile bodies in the system, Mercury lacks a magnetosphere to protect any hypothetical atmosphere or inhabitants from dangerous solar radiation. Unlike other bodies in the system Mercury has all the necessary properties to generate its own magnetic field. Originally when it formed the planet had a magnetic field at least 30% as strong as the Earth's, but a massive asteroid impact stalled this magnetic field (the same impact that likely created the Caloris basin). Before the planet's dynamo core could recover the Sun's immense magnetic field took hold and prevented any further development. Mercury's fledgling atmosphere stood no chance against solar winds and was stripped away soon thereafter.
But even in the billions of years since, Mercury's core hadn't fully cooled. The iron core was still molten and churning and in principle capable of producing a magnetosphere thirty times stronger than it was. Late in the 9th Millenium researchers from the Apollyon Institute proposed a bold plan: kickstart the Mercurian magnetosphere. The idea was that if Mercury could be temporarily protected from solar interference its iron core would restart a magnetic field strong enough to maintain an atmosphere. Assuming that Mercury never experienced another apocalyptic impact like the Caloris event this field would remain stable even under solar wind. 
The research team, now organized under the Hermes Project, proposed a massive magnetic shield be constructed in orbit to protect Mercury for the time required for its magnetosphere to develop. The settled plan would be a massive Faraday shield constructed in orbit around the Sun-Mercury L₁ point. Several thousand kilometers of electrocarbon wire are woven together, forming an artificial eclipse to shield Mercury's core.

Type

Planet