1Astro 102/1041Lecture #19: Mars• Mars: Overview•General properties•Telescopicobservations•Space missions•AtmosphericCharacteristics• Reading:– Chapters 7.1 (Mars), 9.4, 10.4Astro 102/1042The Main PointChanges in the Martian surface and atmosphere have been studied for centuries by telescopes, and more recently even more details have been discovered by spacecraft missions. Astro 102/1043Basic Properties of Mars•Average Distance from Sun: 227,900,000 km (a=1.52 AU)•Orbital period: 687 days•Period of Spin around axis: 24 hours, 37 minutes (= 1 Sol )•Tilt of Martian spin axis: 25.2°(Mars has seasons)•Mass: 6.7x1023kg = 0.11 ME; Radius: 3397 km = 0.53 RE•Surface area of Mars ≈Land area of Earth's continents•Density = 3.9 g/cm3 (little metal; some ice? (Earth: 5.5))•Surface Gravity = 3.7 m/sec2 (38% of Earth's)•Thin CO2-rich atmosphere; Surface pressure ~1% Earth's•Average Surface Temperature: -60°C (-76°F); ΔT ~100°C•Complex surface geologic processes at work...Astro 102/1044Observations•Recall: Mars sometimes has a retrogrademotion•Earth has a "close encounter" with Mars about once every 26 months–Distance varies because Mars' orbit is eccentric•During these times, Mars is a prominent bright "star" in the evening sky–It is noticeably red!–Hence its historic association with blood, war
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