Exploration of Mars seasonal vegetation and apparent linear features were ascribed to intelligent design. Further telescopic observations found two moons, Phobos and Deimos, polar ice caps and the feature now known as Olympus Mons, the solar system's tallest mountain. The discoveries piqued further interest in the study and exploration of the red planet. Mars is a rocky planet, like Earth, that formed around the same time, yet with only half the diameter of Earth, and a far thinner atmosphere; it has a cold and desert-like surface. The minimum-energy launch windows for a Martian expedition occur at intervals of approximately two years and two
Sword and planet Mars" by Edgar Rice Burroughs originally serialized by "All-Story" in 1912 as "Under the Moons of Mars". The genre predates the mainstream popularity of science fiction proper, and does not necessarily feature any scientific rigor, being instead romantic tales of high adventure. For example, little thought is given to explaining why the environment of the alien planet is compatible with life from Earth, just that it does in order to allow the hero to move about and interact with the natives. Native technology will often break the known laws of physics. The genre tag "sword and planet" is constructed to