Venus: Global warming gone bad

Earth & Venus: Sister planets? VenusEarth Mass5x10 24 kg6x10 24 kg a (semi- major axis) 0.7 AU1 AU T at surface~750 K~300 K P at surface~90 atm~1 atm atm composition N2 and H2O clouds CO2 and H2SO4 clouds What is the boiling Temp of water?

How do we know Venus’s surface temperature?

high energy short wavelength “bluer” hot low energy long wavelength “redder” cold

How do we know Venus’s surface temperature? Earth emits light here. T=300 K the Sun emits light here. T=6000 K Venus emits light here. T=750

How do we know what the clouds are made of? Wavelength of light (in the infrared) Amount of light observed above the atmosphere Spectrum of planet with no atmosphere

How do we know what the clouds are made of? Wavelength of light (in the infrared) Amount of light observed above the atmosphere Wavelength at which a molecule in the atmosphere absorbs light Spectrum of planet with no atmosphere Spectrum of planet with atmosphere

How do we know what the clouds are made of? (Infrared light)

How did Venus get so hot? Remember - all gases absorb light at specific wavelengths. “Greenhouse” gases (like carbon dioxide, water and methane) like to absorb in the infrared wavelengths. Planets emit light at infrared wavelengths (same as human bodies). Conclusion? “Greenhouse” gases don’t lett the heat from the planet escape.

How did Venus get so hot? Planetary surface A planet with no atmosphere Solar radiation comes in Planetary radiation goes out

How did Venus get so hot? Planetary surface A planet with an atmosphere Solar radiation comes in Planetary radiation goes out, but gets absorbed The greenhouse gases reradiate. Some of the energy goes towards the surface. Greenhouse gases

How do greenhouse gases get into the atmosphere? Water: evaporation CO2: vaporization of rocks, release from traps, vaporization of biotic material (like fossil fuels), respiration Methane: release from traps, biology (bacteria, cows, rice)

Venus is an example of a “runaway greenhouse”. rocks and water vaporize and release greenhouse gases greenhouse gases heat the surface of the planet Why was Venus hot in the first place?

Earth was also a “runaway greenhouse” at one point! rocks and water vaporize and release greenhouse gases greenhouse gases heat the surface of the planet

Why did the Earth cool, but Venus stay so hot?

Ideas: Oceans? Biology? It probably has to do with water, but why the Earth has water and Venus doesn’t is not well understood. It MAY be that water allowed plate tectonics to occur, and when the oceanic plates subduct, they take CO 2 with them.

The Surface of Venus Venus’s surface can’t be viewed in visible light. The atmosphere absorbs most visible light. Radio light reaches the surface.

Venus’s surface was mapped with RADAR. surface RADAR instrument RADAR instruments can map topography.

Venus’s surface was mapped with RADAR. smooth surface RADAR instrument RADAR instruments can determine roughness. rough surface

Venus’s surface was mapped with RADAR. Reflective surface RADAR instrument RADAR instruments can determine reflectivity. Absorptive surface

Venus’s has few small craters. Why? Venus’s has few large craters. Why?

Venus’s has few small craters. Why? Venus’s has few large craters. Why? Venus has a dense atmosphere. Venus’s surface is ‘young’.

How are craters on Venus different from craters on other bodies? Venus the moon

Venus’s surface is covered with volcanic features. How can you tell impact craters from volcanic calderas? What does the brightness mean in these images?

Venus’s surface is covered with volcanic features. Few craters have been altered by lava. What does this mean? If lava lies over an existing crater, then the crater came first.

Venus: Take-away messages Venus’s bulk properties (mass, size, distance from sun) are similar to Earth. However, Venus’s atmosphere has a lot of CO 2 and therefore its surface is very hot. Exactly why Venus and Earth evolved in different ways is not well understood, but is probably related to water. Volcanism is an important process on its surface, but may not have been active recently. Venus’s entire surface is ‘young’, so some global resurfacing event occurred.