Mars is fourth planet, starting from center Sun.

Like Venus and Earth, Mars owns an atmospher that is very thin , filled mostly with carbon dioxyde  CO 2 (95,32 %), and very few water steam (0,03 %).

Around Mars are two natural satellites: Phobos ("terror") et Deimos ("panic").

Mars, water and life ?

Two major différences between atmosphers of Mars and Earth are :

- very low mass mass of martian atmospher, mainly of carbon dioxyde CO 2 (whose ground pressure is 6 hectopascals, when we have 1   013 hectopascals on Earth)

- average température , much colder (-50  ° C), due to bigger distance from Sun than Earth. In martian year, 20 % of atmospheric carbon dioxyde condenses alternatively on each pole, so we have seasons variations of pressure.

Water steam in atmospher is very low and variable. Composition of atmospher is mainly carbon dioxyde (95,3 %), nitrogen (2,7 %), argon (1,6 %), oxygen (0,2 %) traces of water steam, carbon monoxyde and rare gases.

Mission Mars Global Surveyor did cartography of Red Planet, and studied physical and chemical characteristics , not life on Mars, whatever people interest for that question.

A more delicate debate is to know whether Life existed on Mars once, given evidences of climatic changes, and that atmospher had been in the past warmer and thicker.. Short term answers could come from automatic rangers : Mars 96 then Mars 98 for Russia, Mars Pathfinder for Americans, both having thought of a of a common "Mars Together" in 1998. An analysis from a meteorite from Mars that feel on Earth 13000 years ago, holding bactérian life traces, seems to proof that life could have existed on Mars.