7.4 Venus: A Hothouse World

• Our Goals for Learning • Is Venus geologically active? • Why is Venus so hot? Is Venus geologically active? Cratering on Venus

• Impact craters, but fewer than Moon, Mercury, Mars Volcanoes on Venus

• Many volcanoes Tectonics on Venus

• Fractured and contorted surface indicates tectonic stresses Erosion on Venus

• Photos of rocks taken by lander show little erosion Does Venus have plate tectonics?

• Most of Earth’s major geological features can be attributed to plate tectonics, which gradually remakes Earth’s surface. • Venus does not appear to have plate tectonics, but its entire surface seems to have been “repaved” 750 million years ago. Atmosphere of Venus

• Reflective clouds contain droplets of sulfuric acid.

• The upper atmosphere has fast winds that remain unexplained. Atmosphere of Venus

• Most of the atmosphere is carbon dioxide. Atmosphere is very thick, with a surface pressure 90 times that of Earth. Why is Venus so hot?

The greenhouse effect on Venus keeps its surface temperature at 470°C.

But why is the greenhouse effect on Venus so much stronger than on Earth? Thick CO2 atmosphere of Venus locks heat in Where is Earth’s

CO2? Where is Earth’s CO2?

Carbonate rocks like limestone (plus some in plant life and in the ocean)

Why did this happen on Earth and not on Venus?

Venus lacks oceans to dissolve the carbon dioxide and lock it away in rocks on the seafloor

And why is that? We can understand Venus’ history by thinking about what would happen if Earth were moved to Venus’ orbit.

How would the initial heating affect the oceans and the greenhouse effect? A runaway greenhouse effect would then occur. Eventually, water molecules would break down & escape to space, just as apparently happened on Venus Greenhouse Effect on Venus

• Thick carbon dioxide atmosphere produces an extremely strong greenhouse effect.

• Earth escapes this fate because most of its carbon and water are in rocks and oceans. What have we learned? • Is Venus geologically • Why is Venus so hot? active? • Venus’s extreme surface heat is a • Venus almost certainly remains result of its thick, carbon dioxide geologically active today. Its atmosphere, which creates a very surface shows evidence of major strong greenhouse effect. The volcanic or tectonic activity in the reason Venus has such a thick atmosphere is its distance from the past billion years, and it should Sun: It was too close to develop retain nearly as much internal heat liquid oceans like those on Earth, as Earth. However, geological where most of the outgassed activity on Venus differs from that carbon dioxide dissolved in water on Earth in at least two key ways: and became locked away in rock. lack of erosion and lack of plate Thus, the carbon dioxide remained tectonics. in the atmosphere, creating the strong greenhouse effect.