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Mars. Essential Points. Mars is about half the size of Earth Mars has a thin carbon dioxide atmosphere Mars has volcanoes and faults but no plate tectonics Mars had liquid water early in its history Evidence for life on Mars is debatable. Mars. About half the size of Earth
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Essential Points • Mars is about half the size of Earth • Mars has a thin carbon dioxide atmosphere • Mars has volcanoes and faults but no plate tectonics • Mars had liquid water early in its history • Evidence for life on Mars is debatable
Mars • About half the size of Earth • Rotates in 24.5 hours • Ranges from 207 to 249 million km (129 to 155 million miles) from Sun • Period: 687 days • Two tiny satellites
The Surface of Mars • Thin carbon dioxide atmosphere about 1/150 as dense as Earth’s • Surface temperatures -20 to -200 C • Polar caps of ice and frozen carbon dioxide • Large rift valley (Vallis Marineris) • Huge Shield Volcanoes (Olympus Mons) • Evidence for former liquid water
Modern Imaging Technology Improves Earth-Based Views of Mars Greatly
How to Lose an Ocean • If water is exposed to solar UV and particles, it breaks down to H + O (photo-dissociation) • Happens if water gets into upper atmosphere • Planet gets hot (Venus) • Planet loses atmosphere (Mars) • Oxygen combines with iron and other elements, on Mars may also have escaped