Jupiter, the largest planet in the Solar System, has appeared in works of fiction across several centuries. The way the planet has been depicted has evolved as more has become known about its composition; it was initially portrayed as being entirely solid, later as having a high-pressure atmosphere with a solid surface underneath, and finally as being entirely gaseous. It was a popular setting during the pulp era of science fiction. Life on the planet has variously been depicted as identical to humans, larger versions of humans, and non-human. Non-human life on Jupiter has been portrayed as primitive in some works and more advanced than humans in others. The moons of Jupiter have also been featured in a large number of stories, especially the four Galilean moons—Io, Europa, Ganymede, and Callisto. Common themes include terraforming and colonizing these worlds. Jupiter Early depictions Jupiter was long believed, incorrectly, to be a solid planet that it would be possible to make a landing on. It has made appearances in fiction since at least the 1752 novel Micromégas by Voltaire, wherein an alien from Sirius and another from Saturn pass Jupiter's satellites and land on the planet itself. In the 1800s, writers typically assumed that Jupiter was not only solid but also an Earth-like world and depicted it accordingly. In the 1886 novel Aleriel, or A Voyage to Other Worlds by W. S. Lach-Szyrma, the planet is covered in an ocean with a few islands and primitive aquatic humanoids living there. Jupiter resembles prehistoric Earth with a rich fauna full of lifeforms such as dinosaurs and mastodons in the 1894 novel A Journey in Other Worlds by John Jacob Astor IV. A few utopian works of fiction of the early 1900s are set on Jupiter, including the anonymously published 1908 novel To Jupiter Via Hell and the 1922 novel The Perfect World by Ella Scrymsour. Jovians Most writers portrayed the inhabitants of Jupiter as being human, including Marie Corelli in the 1886 novel A Romance of Two Worlds and Cornelius Shea in the 1905 novel Mystic Island; Or, the Tale of a Hidden Treasure. In the anonymously published 1873 novel A Narrative of the Travels and Adventures of Paul Aermont among the Planets, the human inhabitants of Jupiter have heavier-than-air aircraft. Some portrayed Jovians as giant humans, including Albert Waldo Howard in the novel The Milltillionaire and William Shuler Harris in the 1905