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Solar System


Roman god Mars, Martian day, Roman god of war, diameter of Earth, space probes

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>  Observation from Earth

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>  The Martian Past

>  Spacecraft Missions to Mars

>  Search for Life on Mars

Mars (planet), fourth planet in distance from the Sun in the solar system. Mars is of special scientific interest because of its similarities to Earth. It has an atmosphere with seasons and changing weather, and its surface shows evidence of ancient water and volcanoes. The length of its day and the tilt of its axis are similar to those of Earth. Mars takes about two years to circle the Sun at an average distance of 228 million km (141.7 million mi). The possibility of life on Mars, now or in the distant past, is one of the major questions in astronomy. More space probes have been sent to Mars than to any other planet. Mars is named for the Roman god of war. It is sometimes called the red planet because it appears fiery red in Earth’s night sky, the result of rusty, iron-oxide mineral dust that covers its surface.

Mars is a relatively small planet, with a diameter of about 6,794 km (4,222 mi) or about half the diameter of Earth. Mars has about one-tenth Earth’s mass. The force of gravity on the surface of Mars is about three-eighths of that on Earth. Mars has twice the diameter and twice the surface gravity of Earth’s Moon. The surface area of Mars is almost exactly the same as the surface area of the dry land on Earth. Mars is believed to be about the same age as Earth, having formed from the same spinning, condensing cloud of gas and dust that formed the Sun and the other planets about 4.6 billion years ago.

Mars has two moons, Phobos and Deimos, which are named after the sons of the Roman god Mars. These tiny bodies are heavily cratered, dark chunks of rock and may be asteroids captured by the gravitational pull of Mars. Phobos orbits Mars once in less than one Martian day, so it appears to rise in the west and set in the east, usually twice each day. Deimos has the more ordinary habit of rising in the east and setting in the west.


Bell, Jim, B.S., M.S., Ph.D.

Associate Professor of Astronomy at Cornell University who was in charge of the panoramic cameras on the Mars Rover Expedition. Author of "Postcards from Mars: The First Photographer on the Red Planet".

Article key phrases:

Roman god Mars, Martian day, Roman god of war, diameter of Earth, space probes, small planet, solar system, Deimos, surface of Mars, force of gravity, red planet, Mars, volcanoes, asteroids, night sky, dry land, moons, planets, axis, similarities, astronomy, spinning, tilt, Moon, dust, atmosphere, mass, sons, Earth, seasons, Sun, west, east, length, age, day, years, fiery red

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