Volcanoes Craters and a Grand Canyon

The Mariner series of planetary probes launched in the 1960s and 1970s revealed a startling difference between the southern and northern hemispheres of Mars. The southern hemisphere is far more cratered than the northern hemisphere, which is covered with wind-blown material as well as volcanic lava. There have even been recent proposals that the smooth northern hemisphere hides a frozen ocean.

Volcanoes and lava plains from ancient volcanic activity abound on Mars. Because the planet's surface gravity is low (0.38 that of the earth), the volcanoes can rise to spectacular heights. Like Venus, Mars lacks a strong magnetic field, but, in contrast to Venus, it rotates rapidly; therefore, astronomers conclude that the core of Mars is nonmetallic, nonliquid, or both. Astronomers believe that the core of the smaller Mars has cooled and is likely solid, consisting largely of iron sulfide.

Unlike the earth, Mars failed to develop much tectonic activity (instability of the crust), probably because its smaller size meant that the outer layers of the planet cooled rapidly. Instead, volcanic activity was probably quite intense some 2 billion years ago.

Olympus Mons, found on Mars, is the largest known volcano in the solar system. It is 340 miles (544 km) in diameter and almost 17 miles (27 km) high.

Astro Byte

Olympus Mons, found on Mars, is the largest known volcano in the solar system. It is 340 miles (544 km) in diameter and almost 17 miles (27 km) high.

This Mars Orbiter Laser Altimeter (MOLA) image of the Martian surface shows the famous Valles Marineris region as well as the huge Olympus Mons and Tharsis Bulge regions. The vertical accuracy is 5 meters.

(Image from NASA and MOLA Science Team)

Close Encounter

Close Encounter

While you can see Mars on many nights, it is best seen for a span of a few months every 26 months when it is in opposition: closest to the earth and on the opposite side of the earth from the sun (that is, when the earth comes between it and the sun). Consult one of the annual guides listed in Appendix E for the dates of the next several oppositions. When Mars is at opposition, you can make out remarkable detail, even with a modest telescope, including at least one of the polar caps as well as dark areas (maria or "seas") and contrastingly bright "desert" stretches. Colored filters can help enhance certain surface features such as the polar caps.

Mars is the only planet in the solar system that lets us see its surface in detail; however, even when close during opposition, it is possible that Martian dust storms will obscure its surface.

Also impressive are Martian canyons, including Valles Marineris, the "Mariner Valley," which runs some 2,500 miles (4,025 km) along the Martian equator and is as much as 75 miles (120 km) wide and, in some places, more than four miles (6.5 km) deep. The Valles Marineris is not a canyon in the earthly sense, since it was not cut by flowing water, but is a geological fault feature.

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