Venus

Astronomy 311Professor Lee

CarknerLecture 11

Why does Mercury have 3-2 spin orbit coupling instead of 1-1?

a) Because of the Caloris impactb) Due to resonance with Venusc) Because of its large iron cored) Because it is not quite close enough to

the sune) Because of the relatively high

eccentricity of its orbit

Why do we think there might be water ice at Mercury’s poles?

a) Radar reflects strongly off of polar regions

b) We see the spectroscopic signature of hydrogen

c) The Caloris impactor should have lowered temperatures at the poles enough for ice to form

d) There is evidence of comet impacts at the poles

e) The slow rotation of Mercury is ideal for ice formation

Venus -- The Goddess of Beauty

Romans named it Venus for its beauty symbol for Venus

is a mirror

Venus from Earth

sometimes called the morning or

evening “star” Venus is covered with clouds

clouds reflect ~75% of sunlight

Venus Facts

Size: 95% Earth

Orbit: 0.7 AU

Description: Earth-sized, hot, thick atmosphere (Earth’s evil twin)

Venus’s Retrograde Rotation

When viewed from above the north pole of the Earth, most of the planets: revolve around the Sun counterclockwise

It is upside down

Why is Venus upside down?

We have no evidence of this, however

Retrograde Rotation

Rotation Rate

Venus revolves around the Sun with a period of 225 days

Reason is unclear

impact altered its rotation rate?

Venus from Pioneer

Venus’s Atmosphere

Composition:

Pressure: 90 atmospheres (equal to being 1 km underwater on Earth)

Temperature: 750 K (hottest planet in solar system)

Chemicals in Atmosphere Forms many sulfur compounds including

sulfuric acid (H2SO4) Sulfuric acid has vapor point such that it

boils on the surface but condenses in the atmosphere to form clouds

Also, hydrofluoric acid (HF), hydrochloric acid (HCl) and other corrosive compounds

Temperature in Atmosphere

Formation of Atmosphere1)

2) Water produces greenhouse effect, boils oceans3)

4) With no water, CO2 cannot be removed from atmosphere, thick CO2 atmosphere forms

5)

6) Volcanoes outgas sulfur, forms sulfuric acid clouds

The Surface of Venus

Clouds block blue light so surface appears red, but surface is actually gray

Chemical analysis indicates that

surface rocks are similar to basalt, a volcanic rock

InterludePlanetary Configurations

Magellan Maps Venus

Probes and landers saw only bits and pieces of it

Used radar to penetrate the clouds and map the surface with a resolution of 100 meters

Radar Map of Venus

Global Surface of Venus

Two large highlands or continents (Aphrodite Terra and Ishtar Terra)

The entire surface is the same age

Venus re-surfaces itself

Surface features named after women

Volcanism on Venus

Evidence for Volcanism: sulfur in atmosphere filled craters

Note that volcanoes are not active now

The Interior of Venus With so much volcanism, part of Venus

must be molten, but:

the crust is not broken up into moving plates

Why no plate tectonics? too hot or too dry?

Venus probably has a molten core

Next Time

Read Chapter 7

Summary

Earth-Sized, hot, thick atmosphere (Earth’s evil twin)

Rotates slowly and upside-down Studied by Venera landers and

Magellan radar mapper

Summary: Atmosphere

Composed of CO2 with sulfuric acid clouds

Thick (90 atmospheres) : No water to wash out CO2

Hot (750 K): Powerful greenhouse effect

Summary: Surface

Volcanism shapes surface and outgases sulfur See volcanoes and lava flow channels

Surface mostly flat with a few highlands

Nature of core is unknown