Fifth planet (hypothetical) Fifth planet (hypothetical) In the history of astronomy, a handful of Solar System bodies have been counted as the fifth planet from the Sun. Under the present definition of a planet, Jupiter is counted as the fifth. There are three main ideas regarding hypothetical planets between Mars and Jupiter. During the early 19th century, as asteroids were discovered, they were considered planets. Jupiter became the sixth planet with the discovery of Ceres in 1801. Soon, three more asteroids, Pallas (1802), Juno (1804), and Vesta (1807) were discovered. They were counted as separate planets, despite the fact that they shared an
The Planet of Doubt The Planet of Doubt "The Planet of Doubt" is a science fiction short story by Stanley G. Weinbaum that was first published in the October 1935 issue of "Astounding Stories". It is Weinbaum's third story featuring Hamilton Hammond and Patricia Burlingame, a sequel to "Parasite Planet" and "The Lotus Eaters". Following his expedition to the night side of Venus, the Smithsonian Institution appoints Hamilton "Ham" Hammond to head an expedition to Uranus. In Weinbaum's version of the Solar System, all of the gas giants generate significant amounts of infrared radiation, enough to produce Earthlike environments on the inner moons of