(This planet is in the same universe as Cauldron, Cryolith, Phobis Terra,
and Behemoth, but is not something I'd plan to make a main part of the
actual mod, if it ever gets made. This description is more for my own
enjoyment, and hopefully yours.)
Basic Description
This is the innermost planet in the system. It is about the size of Mercury, and mostly rock and metal, but has a much larger fraction of radioactive material, that powers internal activity on the planet. This activity reshapes the surface, and supplies the planet with a thin atmosphere. The planet is tidally locked, with no moons.
Interior
The planet has a structure resembling most rocky planets, with a metallic core in the center, and a rock mantle and crust as the outer layers. The mantle towards the surface is partly melted, due to the large amounts of radioactive materials near the surface. Most activity in the mantle comes from plumes of ascending and descending material.
The Core of griddle generates a weak magnetic field, though much less strong than Earth's.
Atmosphere
The atmosphere of griddle mainly contains carbon dioxide, sulfur dioxide, and nitrogen, and it is about 1/20 the density of Earth's. The atmosphere is replenished by volcanic gases, and lost to heating by auroras and solar wind action, and large amounts of material freeze on the cold side of the planet. Atmospheric winds largely circulate between the warm to cold sides of the planet, with air near the surface on the hot side rising and flowing towards the cold side, where it sinks to the surface and travels back. These winds do not reach all the way around the planet, leaving a dead zone facing away from the star.
On the section of the planet directly facing the star, temperatures reach around 600 Celsius, due both to the constant sunlight from the star, and greenhouse warming from the atmospheric gases, but heat is quickly transferred by winds towards the night side of the planet. Traveling around the planet, the temperature drops towards the day/night boundary, and continues dropping towards the night side dead zone , where temperatures drop to about -150 C, as heat transported from the day side radiates away. On the night side, the air gets cool enough for carbon dioxide and sulfur dioxide to freeze and form clouds, changing the composition greatly. Atmospheric dust is also common, mostly released from volcanoes.
The atmosphere is constantly being worn away, both by auroras and stellar winds, and by the high temperatures on the warm side of the planet. As a result, most original gases, including water, and been blown away, and the current atmospheric gases are mostly those released more recently by volcanoes.
Surface
Due to the tidal locking, the surface of griddle of quite different on the day and night hemispheres. On the day side, the surface is mostly hot, volcanic rock, with a few dusty areas formed from volcanic dust and eroded rock. The plumes of griddle's mantle form large volcanic mountains on the surface, although most of it is plains, with a few ridges and folded areas, and craters. Due to the high temperatures on much of the day side, and the difficulty the atmosphere has in transferring heat, lava lakes can be maintained for a long time, and rivers and lakes of lava are common sights near dayside volcanoes, with more concentrated near the point closest to the star.
The fart colder night side is largely covered in frost, both carbon dioxide and sulfur dioxide. The frost starts as thin, patchy sections near the day night boundary, and gets thicker and covers a larger section of the surface as the distance from the day/night boundary increases. Near the dead zone, the frost layer gets about a mile thick. Even on this side, the planet is highly active volcanically, and the same pattern of tall mountains, plains, and ridge zones occur, but covered in frost.
Magnetosphere
The magnetic field of griddle is powerful enough and large enough to cover the planet, producing about an Earth sized magnetosphere. Though the field blocks most stellar wind, some does make it through, and powerful stellar wind events push large amounts of material into the magnetosphere, stripping the atmosphere and leading to more widespread auroras.
Explanation
This planet is mostly me imagining a more volcanic Mercury. It isn't based strongly on any other planets or moons, and is mostly me imagining out a world.
