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
Akaa Solar System Scale Model man-made spacecraft) and the concrete pillar representing its location is at the center of the neighbouring town Viiala, approximately 7 km away from the Sun. The speed of light in the scale model is exactly 10 cm/second, so walking the 50-meter distance from the Earth to Sun "at light speed" takes 8 minutes and 20 seconds. In 2018 scale model of Proxima Centauri -star was added to Akaa Solar System Scale Model. Proxima Centauri is a red dwarf star and the nearest star to our Solar System. It is located 4.24 light-years away and in the model's scale it has