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
Phobos monolith astronaut Buzz Aldrin has spoken about the Phobos monolith and his support for a mission to Phobos. The object appears in Mars Global Surveyor images SPS252603 and SPS255103, dated 1998. The object is unrelated to another monolith located on the surface of Mars, which NASA noted as an example of a common surface feature in that region. Phobos monolith The Phobos monolith is a large rock on the surface of Mars's moon Phobos. It is a boulder about across and tall. A monolith is a geological feature consisting of a single massive piece of rock. Monoliths also occur naturally on