This world was once a rogue frozen S-Class body hurtling through the universe until its path was disturbed by Jupiter’s gravity well. It headed towards Sol on a collision course. A small asteroid diverging company decided to attempt to alter its course so that it would become the new first planet of the Sol System. It was basically practice, but they were extremely happy when it worked. The method they used was to change the orbits of a few hundred asteroids so that they swung by the moving planet, then out to Jupiter and then back, using the gravitational attraction to move Vulcan in the desired direction. This slowed its approach and altered its vector so that it would enter into a close orbit of Sol. As the planet approached Sol, the increasing heat from the sun melted long frozen gases on Vulcan and its close orbiting moon Hephaestus, creating atmospheres on both worlds and turning both into hot D-Class worlds.
After the moon settled into its new 18.8 day orbit, the world was settled by a few scientists who would use the opportunity to study Sol. The planet orbited Sol at a mere 0.14 AU and was soon tidally locked.
The new mean temperature of Vulcan was 459.5 °C (859.1 °F) and had a gravity of 1.2 Gs. It has a diameter of 11963.6 km (7433.9 mi). In its past it had obviously seen a bunch of heavy bombardment. Its new atmosphere, which has a pressure of 0.2, can still generate a massive storm near the eternal noon of its day side. It rages constantly.
Vulcan is too close to the sun to terraform so most live near the terminator of the planet. The planet is home to over 1,000 scientists who study the sun.
The world is immensely hot on its day side and relatively cool on its night side. The storm at the planet’s eternal noon blows dust and rocks around as it continuously spins and it also blasts a lot of heat to the night side, warming it a bit.
The planet has a strong magnetic field that deflects much of the radiation.