Vulcan was once a rogue frozen R-Class body hurtling through the universe until its path was disturbed by Jupiter’s gravity well. It headed towards Sol on a collision course with the gas giant. 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 overjoyed 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 closely orbiting moon Hephaestus, creating atmospheres on both worlds and turning both into hot Ae-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 Vulcan provided to study Sol. The planet orbited Sol at a mere 0.34 AU. It has a rotational period of 30 hours.
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 14996 km (9998 mi). In its past it had obviously seen a bunch of heavy bombardment. Its new atmosphere, which has a pressure of 0.2 and is composed mostly of water vapor can still generate a massive storm near the eternal noon of the side facing the sun. 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 has a climate like the former Venus.
The planet has a strong magnetic field that deflects much of the radiation.