Mars 101: The facts and the fictions
Seen through a simple telescope, Mars displays mottled reddish features and its south polar cap.
(CNN) - We know a great deal about the red planet from centuries of work by astronomers and from decades of data beamed back from unmanned spacecraft like the twin Viking landers, which in 1976 became the first spacecraft to land successfully on the planet.
"To a certain extent, we think we know quite a bit about Mars now based upon Viking," said Arden Albee, a mission scientist with the Mars Global Surveyor, a satellite in orbit around the red planet. "But probably a lot of the things we think we know are wrong."
Here's some of what know -- or think we know -- about Mars:
Pack a sweater
Despite its warm, reddish color, Mars is a very cold place. The temperature rarely rises above freezing and can fall as low as minus 225 degrees Fahrenheit (minus 143 degrees Celsius). Even on the warmest days, it only occasionally climbs to zero degrees Fahrenheit (minus 18 degrees Celsius). From day to night it can drop as much as 212 degrees Fahrenheit (100 degrees Celsius).
To everything, there is a season
A Martian year, the time it takes Mars to orbit the sun, takes 686 Earth days. Like Earth, the red planet has seasons because its axis is tilted in relation to the sun. Images from the Mars Global Surveyor and Hubble Space Telescope have shown that the change of seasons is sweeping and violent: A long frozen winter gives way to a summer featuring pink dust storms, with winds up to 300 mph (480 km/h).
It's small -- and could help you lose weight
Mars is about half the size of Earth and has only about one-tenth its mass. That means gravity doesn't pull as strongly there: A 100-pound person would weigh only about 38 pounds on Mars.
The reddish soil takes its color from oxidized -- rusted -- iron. The sky is pink because of red dust in the air.
The Martian atmosphere is 96.5 percent carbon dioxide, with only small amounts of oxygen. Nitrogen, carbon monoxide, argon, neon and krypton are also present.
Little green men
In 1877, Italian astronomer Giovanni Schiaparelli discovered apparent lines in the Martian surface. He called them "channels," but when his writings were translated into English, the word became "canals." Unfortunately, this led some overenthusiastic astronomers to speculate about the existence of life there.
U.S. astronomer Percival Lowell championed the belief that the "canals" carried melted water from the polar ice caps to irrigate crops and bring water to Martian cities.
By 1909, astronomers had shown that even the channels were illusionary, but the belief in intelligent life on Mars lingered. In 1938, Orson Welles broadcast a radio play about a Martian invasion of New Jersey based on H.G. Wells' "The War of the Worlds." Many listeners thought it was real and panicked.
Today, scientists speculate that the planet might harbor hardy microbes at best, rather than little green men, due to the presence of possible underground water sources near the surface, documented in dramatic fashion by Global Surveyor photos in recent years.