Terrestrial planet from the original solar nebula. The Solar System has four terrestrial planets: Mercury, Venus, Earth, and Mars. Only one terrestrial planet, Earth, is known to have an active hydrosphere. During the formation of the Solar System, there were probably many more terrestrial planetesimals, but most merged with or were ejected by the four terrestrial planets. Dwarf planets, such as Ceres, Pluto and Eris, and small Solar System bodies are similar to terrestrial planets in the fact that they do have a solid surface, but are, on average, composed of more icy materials (Ceres, Pluto and Eris have densities of 2.17,
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