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Craters larger than roughly 50 km are named for deceased scientists and writers and others who have contributed to the study of Mars. Smaller craters are named for towns and villages of the world with populations of less than 100,000. Large valleys are named for the word "Mars" or "star" in various languages; smaller valleys are named for rivers.
These lists contain the Sun, the planets, dwarf planets, many of the larger small Solar System bodies (which includes the asteroids), all named natural satellites, and a number of smaller objects of historical or scientific interest, such as comets and near-Earth objects.
Mars has an atmosphere composed mostly of carbon dioxide, with surface pressure 0.6% of that of Earth, which is sufficient to support some weather phenomena. [119] During the Mars year (687 Earth days), there are large surface temperature swings on the surface between −78.5 °C (−109.3 °F) to 5.7 °C (42.3 °F).
A leading hypothesis is that it was formed by accretion from material loosed from Earth after a Mars-sized object with about 10% of Earth's mass, named Theia, collided with Earth. [40] It hit Earth with a glancing blow and some of its mass merged with Earth.
In English, the planet Mars is named after Mars, the Roman god of war, [1] an association made because of its red color, which suggests blood. [2] The adjectival form of Latin Mars is Martius, [3] from which the English word Martian derives, used as an adjective or for a putative inhabitant of Mars, and Martial, used as an adjective corresponding to Terrestrial for Earth. [4]
Terrestrials are similar to Earth, with bodies largely composed of rock and metal: Mercury, Venus, Earth, and Mars. Earth is the largest terrestrial planet. [30] Giant planets are significantly more massive than the terrestrials: Jupiter, Saturn, Uranus, and Neptune. [30] They differ from the terrestrial planets in composition.
Phobos (/ ˈ f oʊ b ə s /; systematic designation: Mars I) is the innermost and larger of the two natural satellites of Mars, the other being Deimos. The two moons were discovered in 1877 by American astronomer Asaph Hall. Phobos is named after the Greek god of fear and panic, who is the son of Ares (Mars) and twin brother of Deimos.
Deimos would look more like a bright star or planet (only slightly bigger than how Venus looks from Earth) for an observer on Mars. It has an angular diameter of about 2'. The Sun's angular diameter as seen from Mars, by contrast, is about 21'. Thus there are no total solar eclipses on