Mars and seasonal cycles of Mars are likewise similar to those of Earth, as is the tilt that produces the seasons. Mars is the site of Olympus Mons, the largest volcano and second-highest known mountain in the Solar System, and of Valles Marineris, one of the largest canyons in the Solar System. The smooth Borealis basin in the northern hemisphere covers 40% of the planet and may be a giant impact feature. Mars has two moons, Phobos and Deimos, which are small and irregularly shaped. These may be captured asteroids, similar to 5261 Eureka, a Mars trojan. There are ongoing investigations
Colonization of Mars of life forms, including humans, to survive unaided on Mars's surface. Some ideas of possible technologies that may be able to contribute to the actual terraforming of Mars have been conjectured, but none would be able to bring the entire planet into the Earth-like science fiction habitat pictured. Mars lacks enough gravity to hold on to any kind of substantial atmosphere, which in turn means that the planet will remain cold and cloudless, and the extremely scarce surface water frozen. Mars has no global magnetosphere as Earth does. Combined with a thin atmosphere, this permits a significant amount of ionizing