Transcript A Brief History of Planetary Science

Venus
Astronomy 311
Professor Lee Carkner
Lecture 11
Why does Mercury have 3-2 spin
orbit coupling instead of 1-1?
a)
b)
c)
d)
Because of the Caloris impact
Due to resonance with Venus
Because of its large iron core
Because it is not quite close enough to the
sun
e) 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 Atmosphere
1)
2) Water produces greenhouse effect, boils
oceans
3)
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
Interlude
Planetary 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