Mercury (0.4 AU) is the closest planet to the Sun and the smallest planet (0.055 Earth masses). Mercury has no natural satellites, and its only known geological features besides impact craters are lobed ridges or rupes, probably produced by a period of contraction early in its history.[1] Mercury's almost negligible atmosphere consists of atoms blasted off its surface by the solar wind.[2] Its relatively large iron core and thin mantle have not yet been adequately explained. Hypotheses include that its outer layers were stripped off by a giant impact, and that it was prevented from fully accreting by the young Sun's energy.[3][4]
Venus
Venus (0.7 AU) is close in size to Earth, (0.815 Earth masses) and like Earth, has a thick silicate mantle around an iron core, a substantial atmosphere and evidence of internal geological activity. However, it is much drier than Earth and its atmosphere is ninety times as dense. Venus has no natural satellites. It is the hottest planet, with surface temperatures over 400 °C, most likely due to the amount of greenhouse gases in the atmosphere.[5] No definitive evidence of current geological activity has been detected on Venus, but it has no magnetic field that would prevent depletion of its substantial atmosphere, which suggests that its atmosphere is regularly replenished by volcanic eruptions.[6]
^Schenk P., Melosh H.J. (1994), Lobate Thrust Scarps and the Thickness of Mercury's Lithosphere, Abstracts of the 25th Lunar and Planetary Science Conference, 1994LPI....25.1203S
^Bill Arnett (2006). "Mercury". The Nine Planets. Retrieved 2006-09-14.
^Benz, W., Slattery, W. L., Cameron, A. G. W. (1988), Collisional stripping of Mercury's mantle, Icarus, v. 74, p. 516–528.
^Cameron, A. G. W. (1985), The partial volatilization of Mercury, Icarus, v. 64, p. 285–294.
^Mark Alan Bullock (1997). "The Stability of Climate on Venus" (Document). Southwest Research Institute. {{cite document}}: Unknown parameter |accessdate= ignored (help); Unknown parameter |url= ignored (help)
