Mars

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..

dust storm over the north pole of Mars, which represents 0.0068% of the total mass of the planets of the solar system.
Crédit & Copyright: Jean-Luc Dauvergne, Francois Colas, IMCCE/S2P, Obs. Midi-Pyrénées

""A planet is a celestial body that is in orbit around the Sun, which has sufficient mass for its gravity outweighs the forces of cohesion of the solid body and maintain hydrostatic equilibrium (spherical), which eliminated any body moving on its orbit. "
This definition was approved August 24, 2006, at the 26th General Assembly of the IAU (International Astronomical Union) by a show of hands of about 400 scientists and astronomers after ten days of talks.

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...

On March, Mount Olympus is a shield volcano, the result of a very fluid lava emerged chimneys of the volcano for a long time.
Olympus Mons is the largest volcano in the solar system, it is perched on a vast plateau of 25 km in height, about three times the height of Everest. Its gradual slopes do not exceed 5 to 10 ° tilt.
This volcano 600 km wide, is bordered by cliffs, it has a caldera 85 miles long, 60 km wide and 3 km deep, in which there are six other craters are smaller collapse Arsia Mons, Pavonis Ascraeus Mons and Mons.
In 2004, the Mars Express probe has photographed the flanks of Olympus Mons, discovering lava flows of very young, older than 2 million years.
Which suggests that the volcano could still be active.

The extraordinary size of Olympus Mons is certainly due to the fact that Mars has no plate tectonics and lava accumulated on this hot spot until that height.
Olympica Nix is the first name assigned to Olympus Mons by the astronomer Giovanni Schiaparelli. Seen from Earth seems this mountain snow, "nix" meaning "snow" in Latin.
Scientists think that is overlain by impermeable layers of clay sediment, containing pockets of water remained in the liquid state by a heat source where conditions are favorable to life creatures extremophiles.

The volcanic Tharsis dome, on which the Martian volcano Olympus Mons is the largest in the solar system.

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

The ramparts of the crater Victoria seen by Opportunity on September 30th, 2006(Credits: NASA).
The robot Opportunity is in use on Mars since January 2004 with its twin, Spirit, in November 2009, he bravely continued to progress despite multiple incidents which he suffered when he was initially designed to run 90 days.

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

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

The two moons of Mars are Phobos and Deimos (fear and terror in Greek), names derived from the son of the god Ares in Ancient Greece.
These moons of Mars may well be captured asteroids from the main asteroid belt between Mars and Jupiter.
They orbit around the planet, a few thousand miles of it, 9 380 km for Phobos and 23 460 km for Deimos.
Both moons are linked to Mars by the forces of tides, always showing the same face of Mars, the Moon compared to Earth. Because Phobos orbits Mars faster than does the planet Mars itself, the tidal forces are decreasing its orbital radius in a slow but steady pace of a few centimeters per year.
In 20 to 40 million years ago a very good chance that Phobos crashes on the Martian surface. Deimos, however, is far enough away that its orbit tends to leave it so much slower.
The names of its moons are an allusion to a Greek, "The God of war arrives, flanked by two satellites (henchmen) fear and terror" in Greek means Phobos' fear 'and Deimos' terror'.

Deimos ground smooth and filled with dust.

Phobos and its characteristic crater Stickney in the lower right in the photo.

In January 2009, Mars Exploration Rovers celebrated the 5th anniversary of the operations on the surface of the red planet.
The sunset on Mars is part of their large legacy of images they have stored during these five years, the surface of Mars.
This image was recorded by the Spirit rover on 19 May 2005.
The image colors have been slightly accented, but are probably equivalent to the color perceived by the human eye of an explorer earth.
The Martian dust particles suspended in the thin atmosphere of Mars, giving the sky a reddish color. The dust also scatter the light blue of the sky that we see before the sun.
The sun sets behind the Gusev Crater, which is a wall along some 80 km.

Because Mars is farther from the sun than the Earth, the sun is less bright and less of a big third, that the Sun seen from Earth.

The sunset on Mars is part of the large legacy of images they have stored during these five years, the surface of Mars.
This image was recorded by the Spirit rover on 19 May 2005.

The image shows a possible mud volcano more than 100 meters in diameter.
It is located in the plains of the northern hemisphere of Mars.
Credit: HIRIS, MRO, LPL (U. Arizona), NASA.

nota : the major components of the Martian atmosphere:
- CO2 : 95.3%,
- N2 : 2.7%,
- Ar : 1,6%,
- O2 :0.13%,
- CO : 0.07%

Mercury

Mars

Uranus

Venus

Jupiter

Neptune

Terre