Relative Similarity To Earth
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The Earth is much like its "sister planet" Venus in bulk composition, size and surface gravity, but Mars' similarities to Earth are more compelling when considering colonization. These include:
- The Martian day (or sol) is very close in duration to Earth's. A solar day on Mars is 24 hours 39 minutes 35.244 seconds. (See timekeeping on Mars.)
- Mars has a surface area that is 28.4% of Earth's, only slightly less than the amount of dry land on Earth (which is 29.2% of Earth's surface). Mars has half the radius of Earth and only one-tenth the mass. This means that it has a smaller volume (~15%) and lower average density than Earth.
- Mars has an axial tilt of 25.19°, compared with Earth's 23.44°. As a result, Mars has seasons much like Earth, though they last nearly twice as long because the Martian year is about 1.88 Earth years. The Martian north pole currently points at Cygnus, not Ursa Minor.
- Mars has an atmosphere. Although it is very thin (about 0.7% of Earth's atmosphere) it provides some protection from solar and cosmic radiation and has been used successfully for aerobraking of spacecraft.
- Recent observations by NASA's Mars Exploration Rovers, ESA's Mars Express and NASA's Phoenix Lander confirm the presence of water ice on Mars. Mars appears to have significant quantities of all the elements necessary to support Earth-based life.
Read more about this topic: Colonization Of Mars
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