10 Additional Planets in the Solar System

Why not, let's throw some extra planets in here.

1. Vulcan

The large, volcanically-active moon of Venus. Hazy atmosphere of mostly C02, and other carbon and sulfur compounds. In extremely close orbit with its parent world.

2. Juno

The 5th Galilean moon: a superterrestrial world of 2.6 Me, with a thick atmosphere of methane, nitrogen, CO2 and ammonia. Frozen, but not as cold as it would otherwise be expected to be, thanks to atmospheric insulation and moderate tectonic activity maintained by the tidal stresses of Jupiter.

3. Janus

A small, rocky world within the orbit of Mercury. No atmosphere to speak of. Tidally-locked to the sun, which has rendered the solar pole a sea of molten stone and metal.

4. Poseidon

A 3.1 Me waterworld between Mars and Jupiter. Dense CO2 and water-vapor atmosphere. Lack of free oxygen indicates that, if there is any life on the planet, it has not evolved photosynthesis or an equivalent process.

5. Apollo

Earth's second moon; a metallic asteroid not even big enough to maintain a spherical shape. A captured body of drastically different composition to Luna, containing economy-devastating amounts of rare earth metals in easy reach.

6. Ixion

A brown dwarf in the Oort cloud, possessing a cluster of small, icy moons. One of these is in close enough orbit that Ixion's radiant heat and tidal stress is sufficient to keep it an icy slush.

7. Dionysus

Captured planet of primarily ethenol ices. Wobbly, extremely elliptical orbit likely to collide with, be captured by, or ejected by Saturn at some point in the future.

8. Athena

A rocky world similar to Mars in terms of size and atmosphere, located among the Greek Camp asteroids at Jupiter's L4 point. Pockmarked surface from eons of meteor impacts, has four surviving moonlets.

9. Hestia

Terrestrial world of 0.62 Me located in Earth's trailing L5 point. Has a somewhat sparse atmosphere and does not appear to have surface water, but there is oxygen and water vapor in the atmosphere and that has people very excited indeed.

10. Persephone

A moon of Pluto. Far too dense for its size and apparent composition. An icy crust sits over unknown contents. There is no proof that it is artificial, not yet, but...