Venus • Venus’ mass and radius are nearly the same as Earth. • Rotation rate is slow and retrograde: 243 Earth days, longer than its year (225 Earth days). Perhaps caused by solar tides and atmospheric friction, or collisional impact. • Atmosphere is incredibly thick (90 times Earth’s, equal to 900 m below sea level) and hot (750 K). • Highly reflective clouds nearly cancels Venus’ proximitiy to Sun, so Venus absorbs only 5% more solar energy than the Earth. • High temperature caused by Greenhouse effect, raising temperature by 470 K (45 K on the Earth, and 5 K on Mars, for comparison) • Surface obscured by sulfuric acid clouds high in Venus’ atmosphere. • Near surface, atmosphere is clear, but density of atmosphere causes peculiar bending of light so that it looks like the bottom of a fishbowl. • Surface explored by radar from Earth and satellites in orbit around Venus. Surface is solid, no lakes, and few mountains. Craters and volcanos exist, but little evidence of plate tectonics, due to absence of water in planet’s crust. • Water is now completely lacking from Venus, but was abundant in past, as deduced from high deuterium/hydrogen ratio in atmosphere, 100 times the value on Earth. • Lack of tectonics also indicated by lesser amounts of Ar40 (from decay of K40) in atmosphere. • Venus evolved divergently from the Earth because it is too close to the Sun.