Lost in Space:
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Outside of the Earth-Moon system, Mars, the fourth planet from the Sun, is the most hospitable body in the solar system for humans. The seventh largest planet in the solar system is at a distance of 4.7 x 107 miles from earth. It has a diameter of about 4,250 miles and it has a mass of approximately 6.4219 x 1023 kg. Mars' orbit is significantly elliptical, which causes a temperature variation of about 30° C. at the subsolar point between aphelion and perihelion. This has a major influence on Mars' climate. While the average temperature on Mars is about 218 K (-55° C., -67° F.), Martian surface temperatures range widely from as little as 140 K (-133° C., -207° F.) at the winter pole to almost 300 K (27° C., 80° F.) on the day side during summer. The interior of Mars is known only by inference from data about the surface and the bulk statistics of the planet. The most likely scenario is a dense core about 1,000 miles in radius, a molten rocky mantle somewhat denser than the Earth's, and a thin crust. Data from the Mars Global Surveyor indicates that Mars' crust is about 50 miles thick in the southern hemisphere but only about 22 miles thick in the north. Mars' relatively low density compared to the other terrestrial planets indicates that its core probably contains a relatively large fraction of sulfur in addition to iron (iron and iron sulfide). Mars has a very thin atmosphere composed mostly of the tiny amount of remaining carbon dioxide (95.3 percent) plus nitrogen (2.7 percent), argon (1.6 percent) and traces of oxygen (0.15 percent) and water (0.03 percent). The average pressure on the surface of Mars is only about 7 millibars (less than 1 percent of Earth's), but it varies greatly with altitude from almost 9 millibars in the deepest basins to about 1 millibar at the top of Olympus Mons. Mars' thin atmosphere produces a greenhouse effect that is only enough to raise the surface temperature by 5 K; much less than what we see on Venus and Earth. However, the atmosphere is thick enough to support very strong winds and vast dust storms that on occasion engulf the entire planet for months. Mars has permanent ice caps at both poles composed mostly of solid carbon dioxide ("dry ice"). The ice caps exhibit a layered structure with alternating layers of ice with varying concentrations of dark dust. In the northern summer the carbon dioxide completely sublimes, leaving a residual layer of water ice. It is not known if a similar layer of water ice exists below the southern cap since its carbon dioxide layer never completely disappears. The mechanism responsible for the layering is unknown but may be due to climatic changes related to long-term changes in the inclination of Mars' equator to the plane of its orbit. There may also be water ice hidden below the surface at lower latitudes. The seasonal changes in the extent of the polar caps changes the global atmospheric pressure by about 25 percent as measured at the Viking lander sites. Part II Questions:
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