Discovery:
In 1609, Galileo Galilei first viewed Mars through a telescope.
Size:
Mars is the fourth planet from the Sun and the seventh largest in our solar system.
Orbit:
Mars orbits the sun at an average distance of 228,000,000 kilometersfrom the Sun. It takes Mars668.98 Earth days to travel around the Sun.
Comparison to Earth:
Of all the planets in the solar system, Mars is the most Earth-like interms of its water patterns. Mars has polar ice caps that grow andrecede with the seasons and has evidence of water channels similar tothose on Earth today.
Terrain:
Mars is mostly ancient, cratered highlands. Thenorthern hemisphere of Mars, however, consists of plains. Mars has adiverse landscape of canyons, mountains, volcanoes, craters and dry river beds.
Interior:
Scientists believe that the dense core of Mars comprises 1,700kilometers in radius; a rocky, molten mantle (denser than the Earth's), a thin crust, and a small core.
Water:
As indicated by its dry river beds, Mars was once home to an abundantsupply of water. The height of its water supply was likely around 3.5billion years ago, when there may have been large lakes and even oceans.Water supply on Mars seems to have lasted for only a brief time, andthen something went terribly wrong. The atmosphere thinned out, and theplanet's ozone layer, if it had one, collapsed, exposing the surface tosterilizing solar ultraviolet light. The rivers and streams evaporatedor froze into the ground.
Exploration:
Mars has been the destination of numerous space missions. In 1965,America's Mariner 4 was the first spacecraft to get a close look atMars. These early pictures, stored on a 4-track tape recorder, took fourdays of transmission to arrive on Earth. Mariners 6 and 7, spacecraftsin the subsequent mission to Mars, took closer pictures of the surface.In 1971, Mariner 9 was the first spacecraft to orbit Mars. A few yearslater, Vikings 1 and 2 landed on Mars for an even closer look atthe planet. It wasn't until 1997 that U.S. spacecrafts again landed onMars. This time, under the Mars Pathfinder mission, which sent landrovers to roam the terrain and analyze rocks. Present exploration ofMars includes two orbiting satellites, a polar cap lander mission, and aprobe mission to learn more about Mars'climate and soil properties.
Atmosphere:
Today, Mars has a very thin atmosphere composed of carbon dioxide,nitrogen, argon and tiny amounts of oxygen and water. The atmosphere isthick enough to produce a small greenhouse effect and to support strongwinds and dust storms that sometimes grip the planet for several months.
Temperature:
The average temperature on Mars is a cold -55 degrees Celsius, or -67 Fahrenheit.
Magnetic fields:
Mars has several weak magnetic fields in various parts of the planet, probably left-overs of a global magnetic field from long ago.
Satellites:
Mars has two small satellites, Phobos and Deimos, which orbit in close proximity to the planet.
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