Phases of Venus

Share Question

How much more solar energy does Venus receive than the Earth, due to the fact that Venus is 0.72 times as far from the Sun?

a) 0.72 times as much b) 1/0.72 = 1.4 times as much c) 0.72 (squared) = 0.52 times as much d) (1/0.72) (squared) = 1.92 times as much

Views of Venus

Transit of Sun

by Venus

Rotation Axis of Venus

A Day at Venus

(Abridged) Exploration of Venus

• 12/62 Mariner 2 (US)• 10/67 Venera 2 (Sov) – 1st surface

contact• 10/75 Venera 9 and 20 (Sov) – 1st

surface photos• 1990-92 Magellan (US) – global radar

mapping

Venera Lander

Magellan Radar Mapping of Venus

Atmosphere of Venus

• Discovered by Lomonosov (Rus.) in 1761

• Venus is almost equally hot everywhere, implying efficient circulation

1) Pole-equator Hadley cell

2) ~360 kph westward flow at cloud level at equator (wind circuits planet in 4 days)

Surprisingly fast wind for a slowly rotating planet!

IR Spectra of the Terrestrials

Earth/Venus Atmospheres

Atmospheric Characteristics

Surface pressure P ~ 90 atms

Surface density ~ 50 E ~ 0.05 H2O

Surface temperature T ~ 720K

Atm. composition CO2

Atm. scale height H ~ 16 km

Cloud layer 44 km

Cloud composition Sulfuric acid

Reflected sunlight ~ 80%

Sunlight at surface ~ 2.5%

Temperature Profile of Venus

Greenhouse Effect (Carl Sagan, 1962)

• Selective Absorption:CO2 absorbs IR better

than visible lightSun emits mostly at 0.5

microns, but planet surfaces glow mostly around 3-30 microns

Suggests there is more energy getting in than out!

• Radiative Equilibrium: (RE)

RE demands that energy in and out must balance!

The trapped (blanketed) energy heats up surface, which becomes brighter.

Continues until the fraction escaping from below equals the total getting in from above.

The Greenhouse Effect

Surface Properties

• Mostly rolling volcanic plains of basaltic rock– No active volcanoes observed, but– Young surface

• Many volcanoes, mostly of shield type

• Fluctuating SO2 levels

• Few impact craters

Volcanic resurfacing has been important!

Venusian Terrain

Volcanos at Venus

Results from Venus Express

Venus May Have Active Volcanism

• Venus has few impact craters, suggesting the entire surface is younger than 1/2 billion years

• Venus has clouds of SO2 (a volcanic gas) and many volcanoes - but active volcanism has not been detected

• New infrared observations indicate some regions were resurfaced in the last 100’s to 10,000’s of years. Venus was recently (and still may be) volcanically active.

Radar and topography “image” from the Magellan spacecraft of Idunn Mons on Venus, which was recently volcanically active. Dark regions are smooth, and bright regions are rough or steep. Elevations have been exaggerated thirty times.

• Thermal emissivity indicates how efficiently a material radiates heat

• Some volcanic regions of the Venus surface have higher emissivity than their surroundings

• Lower emissivity regions have reacted chemically with CO2 and SO2 in the atmosphere, forming a thin crust over the lava

• High emissivity indicates younger material that has not been substantially weathered by Venus’ thick atmosphere

Interpreting Surface ‘Hot Spots’

Infrared observations from the Venus Express spacecraft overlaid on the image from the Slide 1 show that Idunn Mons (red) has higher thermal emissivity than its surroundings (blue). This indicates a compositional difference between the two regions.

The Big Picture• Scientists debate whether the

entire planet was resurfaced in a large global event, or gradually over time

• The new observations of localized recent volcanism suggest that the global hypothesis can not be the entire story. Some scientists believe the results strongly support the gradual hypothesis

• The three regions in this study are all geologically similar to Hawaii, where hot material from deep inside the planet causes uplift and volcanism at the surface. Global radar image of Venus from

Magellan. The approximate location of Idunn Mons, from previous slides, is indicated.

Venusian Relief Map

Venusian Interior

• Similar to Earth’s• However, no magnetic field

Venus’ slow rotation implies little circulation in core

NO DYNAMO ACTIVITY• No evidence for plate tectonics, large

crustal motions, or mountain ranges