Mars is the beloved celestial body of several astronomers' generations. It is the only planet the ground of which we see well since our ground observations. Mars is smaller than the Earth, its diameter is 6500 km, its mass reaches only the tenth of that of our globe, its average density is nearby 4.
It is visible all night long when Mars and the Sun are set in the sky with regard to the Earth.
It is at this moment there that it is in closer of the Earth (56 million km), it shines then as much as Sirius. These oppositions follow each other in intervals of 2 years and 50 days. In most farther of the Earth it is 250 million km.
This beautiful planet appears at the glances as a star of a red blood, it is maybe for that that it carries God's name of the war. Its revolution around the Sun lasts about 700 days. The duration of day is nearby of ours 24H37mn.

Its axis of rotation is close of our, 25°. The public who looks at Mars in a telescope, imagines himself that he is going to contemplate what he sees in the best works reproducing the magnificent photos on glazed paper. It not is nothing; a yellow, vague ball, salts, trembling, here is what sees the simple curious. It is because the aspect of Mars is dependent on bustles and turbulences of the atmosphere. We see well Mars in the telescope or in the glasses only some nights during the period of nearness, that we call the opposition.
Its poles show themselves snowy, this snow bottom almost completely during the Martian summers. Noted: a planet is more brilliant, it shines with a constant brightness among stars. Planets sparkle less than stars. To identify planets it is necessary to get acquainted with the stars of the zodiac because they follow the  ecliptic We call ecliptic the big circle of the heavenly sphere crossed by the Sun in its visible movement around the earth. In one year the earth describes around the Sun, an orbit the plan of which makes an angle of 23°27' with the heavenly equator. The Sun so appears to move by crossing twelve signs of the zodiac: Aries, Taurus, Gemini, Cancer, Lion, Virgo, Libra, Scorpio, Sagittarius, Capricorn, Aquarius, Pisces..

Mariner 10 returned photos of the surface of Mars with a 200 meters resolution. Mars reveals the biggest known volcanoes. The relief of Mars is much more varied and tormented that that of our satellite.
The biggest volcano, Olympus Mons, is 25 km in height, 600 km in width and a crater 20 km in diameter.
In the regions of Tharsis, volcanoes form adaptations as the ground volcanic chains. There are real canyons of rivers, with tributaries branched out in nervures, as on Earth, but these valleys are dry. The biggest canyon, Coprates, is 3000 km in length. All its volcanoes are put out since 300 million years.

This planet knew violent seismic adventures, its lighter coat than that of the Earth can free more easily its constraints. But the cooling faster than to us precipitated the end of the volcanism. Mars also possesses polar skullcaps covered with a white ice which shrinks gradually in summer leaving a residue of dry ice. We detect on Mars a tremendous wind of sand which darkens the atmosphere of the planet rich in carbon dioxide. We discovered it dunes as those of Sahara. There is no magnetic field and the atmosphere of Mars consisted mainly of carbon dioxide and nitrogen, has a pressure on the ground of the order of the fifth of the ground pressure.

The mission Viking, had to put down two automatic vehicles on Mars and return the proofs of the existence of life on the planet. Regrettably this disappointing mission, made on a powdery Martian ground, sprinkled with fragment of rocks taught nothing to us of very clear, to part that there is no life over March. This mission only allowed the specialists to agree on the idea that, in past, Mars had had a meteorology with rains and streaming of water today stored in the ground and in the icecaps. This water doubtless constituted the residual polar skullcaps of the Martian summer.
Mars is a fascinating planet of which we have a lot to learn...

Stratified rocks situated at the top of the low plateau " Home Plate "
(Credits: NASA)

The ramparts of the crater Victoria seen by Opportinity on September 30th, 2006(Credits: NASA)

The rock situated in the top of this image could be a meteorite. Photo taken by Rover Spirit on April 12th, 2006
( Credit: NASA)

category : planets 

The tectonic breaks affected by the region of Candor Chasma in Valles Marineris.
We can see erosions there create by fluids along ravines.

( Credits: NASA - size: 1,6 Mb - Image taken on December 2nd, 2006 - it covers a region of one km wide)