My criterion for which bodies are included in this series isn’t set in stone. I’ve used the flimsy term “world” to basically mean spherical or near-spherical objects. Thus we go to the “4.5th” planet, Ceres.
Ceres has the technical classification dwarf planet and is the largest body in the asteroid belt, but that’s still fairly small compared to planets and large moons. Still, it’s large enough to be round and hence large enough for me. It’s the first object in our journey that wasn’t known in ancient times, only being discovered in 1801. This will be a short one.
Modern Exploration of Ceres:
- Dawn (2015?) – NASA orbiter that’s currently investigating the asteroid Vesta and will leave its orbit to arrive at Ceres in 2015. It carries three scientific instruments and will deliver the first close-up, high resolution photos (the above image is from the Hubble) of its surface and thus Ceres will become the first “new world” since Voyager 2 visited Neptune in 1989.