Despite several missions to Venus there is still much that is unknown about our celestial neighbour. The Russian Venera landers touched down in the 1980s and survived the hostile environment for about 60 minutes during which time images were taken revealing a barren world. Other missions to Venus, both Russian Venera orbiters, and NASAs Magellan spacecraft have concentrated on radar mapping the surface.
From the data returned by these missions scientist believe that the surface of Venus is relatively young - it appears to have undergone resurfacing around 400 million years ago. The topography consists of vast plains and mountainous regions.
Impact craters cover the surface. Unlike other worlds, however, there are virtually no craters less than 2 km in size. The impactors that would cause them simply burn up in the thick atmosphere. Those that do exist are believed to be caused by the fragmentation of a large meteorite just before impact with the surface.
Venus Transits
When Venus passes directly between the Earth and the Sun, this event is called a transit of Venus. Venus orbits the Sun at a smaller distance than does the Earth, so one might expect that Venus transits would occur often. However, the orbital plane of Venus is not parallel to that of the Earth, so transits occur very rarely - only four times every 243 years.
The last Venus transit occurred in 2004; the next will occur in June 2012, although unlike the 2004 transit this one will not be visible in its entirety from Europe. After that, the following transit will not occur until 2117.
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