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,
Gustav Holst to another house in Cheltenham, where Adolph recruited his sister Nina to help raise the boys. Gustav recognised her devotion to the family and dedicated several of his early compositions to her. In 1885 Adolph married Mary Thorley Stone, another of his pupils. They had two sons, Matthias (known as "Max") and Evelyn ("Thorley"). Mary von Holst was absorbed in theosophy and not greatly interested in domestic matters. All four of Adolph's sons were subject to what one biographer calls "benign neglect", and Gustav in particular was "not overburdened with attention or understanding, with a weak sight and a weak