Observing Projects 8D Surveying the Martian Geography Quadrant 1 Centered on 45 Degrees

Mars is a world much like the Moon in geological diversity and though we can't see nearly the detail in Mars that we can in the Moon, it offers us a lot of interesting things to see in what is there. To begin working this project, the first thing you will need is a global topographic map of Mars. You can find this on several Internet sites or if your astronomy software has a sufficiently detailed Mars model, it will suffice.

The first thing you always notice right away about Mars is the highland versus lowland dichotomy. As we discussed earlier, Mars has two distinctly different surfaces separated by thousands of meters of average elevation. Highland areas dominate the south, while the lowlands dominate the north. This strange split personality defies any likelihood that mere chance caused this. But the alternative is that something catastrophic occurred early in the planet's history.

A map of Mars uses a latitude system that is identical to that used on Earth. The longitude system used however has one important difference. On Earth, longitude is counted in both the easterly and westerly directions from a designated prime meridian that runs through the Royal Greenwich Observatory in England. On Mars, there is a designated prime meridian but longitude is only counted upwards in a westerly direction for a full 360 degrees around the planet. In this project we will survey the planet in four quadrants, first from 0 to 90 degrees, then in 90-degree increments traveling westward around the planet.

In our first project, we will view the planet starting with the 45 degree meridian as the central meridian and working 45 degrees on either side. In this way, we are never viewing close to the Martian limb where foreshortening makes it difficult to see objects with clarity. The most prominent feature visible in your telescope here is the large dark area just south of the equator. This area, known as Mare Ery-

tharaeum, is a highland area. The large bright area to its north is Chryse Planitia. This is a broad, flat low-lying plain, which holds a special place in Martian history. It is where the first successful visitor from Earth arrived. On July 20,1976 the Viking 1 lander set down in the northern region of Chryse near a smaller dark area that is at about 30 degrees latitude called Nilokeras. Not far to the east of Viking 1, about a thousand kilometers, is where in 1997 the Mars Pathfinder bounced to a stop on the spot now called Sagan Memorial Station. A large broad dark area to the north and east of Nilokeras, which extends well towards the north Martian pole, is called Mare Acidalium. Even though this area is similar in color to Erytharaeum, Acidal-ium is a lowland area, some of the lowest on Mars. South of the Erytharaeum area is a broad open highland area called Argyre. This plain is a bit lighter in color than Erytharaeum. Mare Oceanidium is located south of Argyre and is much more bright in color than Argyre. As we look further towards the south pole of Mars, the terrain becomes much more mountainous for a distance before giving way to another broad flat plain called Mare Australe. This broad flat highland will eventually give way to the south polar cap.

The most prominent geological feature within this first quadrant is the famous Valles Marineris. This massive canyon is the longest such structure in the solar system. The Valles Marineris extends westward away from Mare Erytharaeum towards the 90-degree meridian about 10 degrees south of the Martian equator towards the Tharsis region, which we explore next. With Mars at its best and the skies clear and calm and with the planet favorably placed, you might be able to trace the hairline of Valles Marineris across the Martian disk.

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