Goal: To understand the differences between Venus and Earth 1)To learn about how Venus’s atmosphere is strange. 2)To understand what caused Venus’s atmosphere to be so strange. 3)To Probing the surface and to understand what can learn from that. 4)To examine the strange surface features of Venus. 5)To discover what is missing from the surface of Venus and what that tells us about Venus.

Venus! Same size and composition as the earth. 25% closer to the sun. Vastly different!

Probing Venus: First probe sent by Russia in 1959 (shortly after Sputnik). The first few attempts failed… Venera 3 landed in 1965, but was destroyed on impact. Venera 4 in 1967 parachuted to the surface, but crushed before it reached the surface (at altitude of 25 km).

More probes By 1970, and Venera 7, Russia made a probe which could withstand higher temperatures for a short time period. The temperature was measured at 748K!

Venus’s current atmosphere: Carbon Dioxide 96.5% (vs 0.03% on the earth) Nitrogen 3.5% Water Vapor 0.003% Sulfur Dioxide 0.015% Surface pressure: 90 bars! Which planet has more total Nitrogen in its atmosphere, Venus or Earth?

Nitrogen? Earth has 78% Nitrogen in its atmosphere. At 1 bar total atmosphere that is 0.78 bars worth of Nitrogen. It would seem that Earth should have move. However… 90 bars * 0.03 = 2.7 bars. Venus has almost 4X more Nitrogen that Earth.

Where did it go? Where is Earth’s Nitrogen?

Where did it go? Where is Earth’s Nitrogen? On earth, it is locked up in the crust by living organisms (after all fertilizer is mostly Nitrogen).

So, what is the consequence of this atmosphere? Carbon dioxide is a greenhouse gas! On Venus the atmosphere is so thick that effectively you have more than 1 greenhouse layer. The lowest layer is heated by the layer above it, and when it radiates energy, half goes to the surface, and half goes to the layer above. The layer above absorbs that, then emits energy half down to the layer below, and half upwards.

But… With 90 bars of mostly atmosphere, you have more than 2 layers! You effectively have over 30 layers! Try going outside on a hot summer day with 30 coats on… So, you can imagine what the surface temperatures is like...

Temperature profile of Venus From textbook. Acid rain clouds are km in the atmosphere, and end at a atmospheric pressure 0.05 bars. This is the same range you get clouds on earth.

Why?! Lets go back to the formation of the earth. At one point the earth had 250 bars of water vapor and about 60 bars of carbon dioxide in its atmosphere. Venus would have had the same start. The earth made a race against time to cool the planet with constant attempts to rain while volcanoes released more and more gasses into the atmosphere.

So… On Earth, the water won. Rains finally succeeded, and the oceans were formed. The Carbon Dioxide dissolved into the rainwater and ended up in the ocean. Venus, however, is a little closer to the sun. So, on Venus, it was just warm enough that the water did not win.

Also The water in Venus’s atmosphere was also quickly destroyed! There are 2 ways to do it. 1) UV rays break apart water high up in the atmosphere to separate the Hydrogen from the Oxygen and the Hydrogen escapes.

UV dissociation No oxygen means no ozone. No ozone means no Stratosphere. With no Stratosphere, water vapor can go to the top of the atmosphere and UV rays can penetrate down into the lower atmosphere.

2 nd method Slow rotation means almost no magnetic field. On the earth, our magnetic field protects us from Cosmic Rays and the solar wind. Without this protection, the highest level of the atmosphere gets bombarded by the solar wind. The solar wind can destroy water molecules.

Result: The result is a very dry atmosphere which has a lot of carbon dioxide with no way to remove the carbon dioxide. It could be worse though, all those clouds and Sulfur Dioxide reflect 75% of the sunlight. It could actually be hotter on Venus!

How to look at the surface: In any telescope, you will only see clouds! So, you need radar to see the surface. Several spacecraft have orbited Venus with radar. Altitude: time to take radar to get back determines altitude! So, you can make topographical maps of the surface of Venus!

Surface map of Venus (from textbook)

Venus Surface features 90% of Venus is very flat (within 1 km). Flatter than the great plains. Lot of volcanoes. About 50k. Some are active! However activity is about 1/5 th of Earth’s.

Small and Medium

Collapsed Domes

Large Volcanoes

Calderas

Lava Flows

Coronae Areas of rising magma

What is missing?

Craters! There are < 1000 craters on the surface of Venus. Erosion? Nope, no water, and not a lot of wind. Lava? Nope, the craters are distributed randomly – even in regions with flows. Atmosphere? The atmosphere destroys any object < 1 km in diameter (in fact there are many places where the surface is scorched because of an explosion within a few km of the surface). However, you still expect more.

Solution: Somehow, the surface of Venus is < 500 million years old, and maybe as young as 250 million. How could this be? Not from erosion, there is no plate tectonics. Lava does not seem to be the culprit.

Young surface: Venus has had a cataclysmic event occur about million years ago. Two main possibilities: 1) giant impact which melted the surface 2) normal Venus cycle (if the Sulfur in the atmosphere goes away, then the surface gets hotter, and can melt – recreating the volcanoes which put back the sulfur and it unmelts).

Conclusion Venus is a very hostile world with a think atmosphere and extremely hot temperatures – even at night. Venus has a lot of strange surface feature. Lots of volcanoes, but is very flat! The surface of Venus is strangely young. This is the, what can go wrong story if a planet has a run-away greenhouse effect (porridge is too hot).