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Mars is a red desert planet with a thin atmosphere composed mainly of carbon dioxide. It experiences greater thermal extremes than Earth and has evidence of liquid water. Olympus Mons is the tallest mountain and Valles Marineris is the largest fissure in the solar system. Olympus Mons is a shield volcano and Valles Marineris is a tectonic feature caused by subsurface volcanism.
Mars is a desert planet covered in iron oxide (rust), which gives it its red color and the nickname “red planet”. The planet has a thin atmosphere composed mainly of carbon dioxide, just 0.6% thick than Earth’s. The atmosphere on Mars has a similar pressure to Earth at an altitude of 35 km (22 mi). Surface temperatures range from −140 °C (−220 °F) during winter to highs of up to 20 °C (68 °F) in summer. Like all planets without bodies of water to modulate their temperature, Mars experiences greater thermal extremes than Earth.
While there is evidence that liquid water has flowed to the surface of Mars in small amounts in recent years, it is likely a rare event, as most of the H2 sublimes (goes directly from solid to gas) rather than passing through a stage liquid. Some Earth-hardy microbes would be able to survive in the Martian environment and may already have been introduced by Mars rovers that have been sent there in recent decades.
Mars features the tallest mountain and volcano in the solar system, Olympus Mons (height: 27 kilometers, 16.7 miles, 88,580 feet) and the largest fissure in the solar system, Valles Marineris (4,000 km (2,500 mi) long, 200 km (125 mi) wide and up to 7 km (4 mi) deep). Like the Moon, Mars is a mix of lower plains covered in lava flows and ancient plateaus with numerous craters. Unlike the Moon, the lava plains of Mars are the lightest parts, covered in iron oxide dust, while the highlands are darker.
The origin of both Olympus Mons and Valles Marineris is quite interesting. Olympus Mons is a shield volcano, like Mauna Kea in Hawaii, that is actually the tallest mountain on Earth when measured from the ocean floor. This means that it is much wider than it is tall and results from many eruptions over a long period of time. Mars lacks plate tectonics, so a volcanic hotspot keeps pushing lava through the same crust, leading to volcanoes of this size. Some of this volcanic activity took place up to two million years ago, based on analysis of the frequency of impact craters on cooled magma flows.
Valles Marineris is a canyon so large that it spans a fifth of the entire Martian equator. If superimposed on Earth, Valles Marineris would extend across the United States, from San Francisco to New York. The canyon is so large that historically scientists have had a hard time determining its origin. At first, some thought the valley might have been carved by a small planet-sized asteroid that scraped across the Martian surface but never fully impacted. Today, most scientists agree that the scarp is a tectonic feature caused by the stretching and cooling of the Martian crust due to subsurface volcanism.
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