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| | ch8 |
 | | An orbiting Mariner spacecraft had surveyed the whole of the planet Mars and revealed unexpected surface features, a planet that was partly primordial and partly molded by volcanism and atmospheric effects. |
 | | These new data, combined with Mariner's direct, highly precise measurements of hydrogen, helium, carbon and argon abundances, provided better insight into the processes by which planetary atmospheres evolve and are modified by the Sun. |
 | | Mercury was known to be a slowly rotating planet, and the early Mariner 10 pictures had shown it to be one which, like the Moon, had not experienced significant crustal modification by internal activity since its infancy. |
| history.nasa.gov /SP-424/ch9.htm (2073 words) |
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