Mars is the fourth planet from the Sun and the seventh largest: Orbit: Diameter: Mass: 227,940,000 km (1.52 AU) from the Sun 6,794 km 6.4219e23 kg

Astronomy

Mars has been known since antiquity. It is still a favorite of science fiction writers as the most favorable place in the Solar System (other than Earth!) for human habitation. Perhaps this is in part because Mars is (or was) the planet most like Earth.

A day on Mars is only 40 minutes longer than an Earth day, and Mars has seasons of summer and winter. On a summer day, however, Martian temperatures reach only 0 degrees C (32 degrees F), which is the temperature at which water freezes. At night, temperatures plunge to -80 degrees C (-110F), close to the temperatures you might expect in the Antarctic winter on Earth. During the Martian winters temperatures fall to -125 degrees C (-190 F), freezing the Martian atmosphere into caps of carbon dioxide ice at the poles.

Rivers almost certainly flowed across Mars millions of years ago, and an ocean may have covered about half the planet. However, we know now that the famous "canals" that Lowell and others thought they saw across the surface of Mars, were not aqueducts that indicated intelligent life. As with Earth, almost all of its carbon dioxide was used up to form carbonate rocks. But lacking the Earth's plate tectonics, Mars is unable to recycle any of this carbon dioxide back into its atmosphere and so it cannot sustain a significant greenhouse effect and trap heat. The surface of Mars is therefore much colder than the Earth would be at the same distance from the Sun. Large but weak magnetic fields exist in various regions of Mars. Its orbit is significantly elliptical, something that has a major influence on the climate. Mars is much smaller than Earth, with its surface area about the same as the land surface area of Earth (approximately 1/3 the surface area of Earth). It is a planet of towering volcanic peaks, the tallest of which is Olympus Mons. Earth's Mt Everest is only one third its size, and the Grand Canyon in Arizona in the USA would seem insignificant beside Valles Marineris, the largest Martian canyon.

Mars is easily visible to the naked eye at night. Its apparent brightness varies greatly according to its relative position to the Earth.

If you would like to know more about the solar system, Starscine suggests the following websites:

www.nineplanets.org
www.nasa.gov