Geography of Mars

Areografie or Areographie (from the Greek for Mars and Greek Ares Άρης γράφειν gráfein for describe ) refers to the geography of Mars, so the investigation, description and mapping of the surface structures of the fourth planet of our solar system. Its southern and northern half are significantly different, which is called a dichotomy of Mars. The northern hemisphere consists mainly of a single low- level, while the southern hemisphere is located five kilometers above the level of the northern plains.

Geodetic and cartographic definitions

Coordinates

How on earth ellipsoidal coordinates are used, but you have to relate with higher accuracy because of the dichotomy is not a (biaxial ) spheroid, but rather a triaxial ellipsoid. They are called areografische coordinates; their latitudes are counted from the date fixed by the rotation equator, all meridians pass through the two rotational poles. The prime meridian is defined by the small, slightly south of the equator lying Mars crater Airy -0. This crater has a diameter of 500 meters having is within the larger crater Airy, which was named after the English astronomer George Biddell Airy, its used for observations at the Royal Greenwich Observatory definition of earthly Nullmerdians was adopted internationally in 1884.

Airy in turn is within the striking dark appearing out of the earth " Meridian Bay " ( Sinus Meridiani ). This was used by the German astronomer Wilhelm Beer and Johann Heinrich Mädler their carried out in the 1830s observations as a feature, by means of which they determined the period of rotation of Mars. This simply of Beer and Mäder "A" mentioned feature was made in 1877 by Giovanni Schiaparelli used to define the zero meridian for his Mars tickets. The data from Mariner 9 in 1972 necessitated a more precise definition, what you the crater Airy -0 chose.

Height

Earlier models maps defined zero level above the atmospheric pressure, namely a pressure of 6.1 mbar was chosen as the reference pressure. This value corresponds to the average pressure in the Martian atmosphere and coincidentally also the triple point of water approximately. This means that only in areas of the Martian surface may theoretically in liquid form below the zero level of the water. Especially seasonal movements in the Martian atmosphere result in a definition of the zero level above atmospheric pressure to inconsistencies. Therefore, a Areoid was determined according to the geoid on the ground, which is defined by an equipotential surface of gravity. This definition was chosen in relation to the definition previously used by the pressure of 6.1 mbar.