# The first impacting body was a body the size of [[Mars]] that struck Venus hard enough to remove some of its mass. This is similar to the giant-impact theory of the origin of the [[Moon]] of [[Earth]]. In Venus's case, the impacting body did not distort the gravity of Venus enough to allow escaping material to accrete into a moon, or a moon did form but then escaped the gravity of Venus entirely. The main difficulty with this theory is that such escape might have required tens of billions of years, longer than a reasonable age of the solar system or even of the [[universe]].
# The second impacting body stopped or reversed Venus's rotation and also so altered the gravity field of Venus that its moon spiraled inward and ultimately crashed onto Venus and added back to its mass.
== Young Surface ==
Today, the surface of Venus is very young and has a relatively low number of craters in comparison to most other terrestrial bodies in the solar system including the moons of various planets, asteroids, Mars, Mercury, and even the Earth. This could possibly be explained in part by the very dense atmosphere of Venus which burns up most small objects that attempt to reach it's surface, creating meteors. The young surface can also be attributed in part to the high level of volcanic activity on Venus. Venus is one of a handful of notable solar system bodies including the Earth, [[Io]] and [[Triton]] which have various degrees of observable activity. On Venus, the combination of high levels of volcanism to constantly repave the surface of the planet combined with the dense atmosphere to protect the fresh volcanic flows provide for the young appearance of the planet.
== Problems with uniformitarian theories ==
# The lack of impact craters forces evolutionists to admit that the surface of Venus appears relatively young. Scientist David Grinspoon suggests that "something dramatic happened on Venus which wiped out almost all signs of an older surface."<ref name=Bortman/> This, Grinspoon says, happened 600 or 700 million years ago. Venus has little to no wind, and any surface liquid water assumed by scientists would have long since evaporated. Therefore the youthful appearance of the surface remains very difficult to explain.# Grinspoon also assumes, without discernible warrant, that Venus once had liquid-[[water]] oceans that have since evaporated.<ref name=Bortman/> Their sole grounds for so stating is that if Earth formed with such vast surface oceans, so Venus should have. Yet the atmosphere has no more than 20 ppm of water today. Moreover, the extensive explorations of Venus by both orbiters and landers has revealed no geological evidence that Venus ever had an ocean. (The conventionale explanation is that the resurfacing of Venus alluded to above would have destroyed any such evidence.)
# Venus rotates retrograde to its orbit around the Sun. Nearly every other Solar System body rotates prograde. This presents a serious theoretical problem for the [[nebular hypothesis]] of the origin of the solar system. The usual suggested solution is a giant impact, or a series of impacts, that somehow reversed Venus' direction. But such models must also explain why these impacts left Venus in an almost circular orbit and with an axis tilted less than three degrees from being perpendicular to its orbital plane.