Lecture 19

Outline• Discuss Quiz

• Mercury

• Venus

Outline For Rest of Semester• Oct. 29th Chapter 9 (Earth)• Nov 3rd and 5th Chapter 9 and Chapter 10 (Earth and Moon)• Nov. 10th and 12th Chapter 11 (Mars, Venus, and Mercury)• Nov. 17th and 19th Chapter 12 (Jupiter and Saturn)• Nov 24th Chapter 13 (Uranus and Neptune)• Nov 26th Thanksgiving• Dec. 1st - Exam 3• Dec. 3rd – Chapter 14 (Pluto, and the Kuiper Belt)• Dec. 8th and 10th – Chapter 7 and 8 (Comparative Planetology I and II)• Tuesday December 15th (7:30 am – 10:15 am) Final Exam• No Reading days are scheduled this semester• Exam Period begins at 7:30 a.m. on Monday, December 14 and ends on

December 21

Mercury

Observations• Observing Mercury

– What are best conditions to observe?• Unusual spin

– How suspected to be unusual– Why unusual– How verified– How to make a guess that will make you famous

• Craters– How similar to the moon– How different

• Unexpected magnetic field– Why unexpected– How measured

Observations• Observing Mercury

– What are best conditions to observe• Unusual spin

– How suspected to be unusual– Why unusual– How verified– How to make a guess that will make you famous

• Craters– How similar to the moon– How different

• Unexpected magnetic field– Why unexpected– How measured

No-name rotation

synchronous rotation 1-to-1 spin-orbit coupling

The Moon’s rotation always keeps the same face toward the Earth due to synchronous rotation

Mercury’s orbital period is 88 daysMercury’s rotation period is 58 days

A

B

C

D

Draw ball and arrow at A, B, C, D

Mercury’s orbital period is 88 daysMercury’s rotation period is 58 days

A

B

C

D

Draw ball and arrow at A, B, C, D

A few days later …

Mercury’s orbital period is 88 daysMercury’s rotation period is 58 days

A

B

C

D

Draw ball and arrow at A, B, C, D

88/4 = 22 days to get to A

22/58 = 0.375

Mercury’s orbital period is 88 daysMercury’s rotation period is 58.6 days

A

B

C

D

Draw ball and arrow at A, B, C, D

88/4 = 22 days to get to A

22/58 = 0.375

First move into position in orbit. Then rotate around Mercury’s axis.

Mercury’s orbital period is 88 daysMercury’s rotation period is 58 days

A

B

C

D

Draw ball and arrow at A, B, C, D

88/4 = 22 days to get to A

22/58 = 0.375

D

0.375 of a full turn

Mercury’s orbital period is 88 daysMercury’s rotation period is 58 days

A

B

C

D

Draw ball and arrow at A, B, C, D

88/4 = 22 days to get to A

22/58 = 0.375

D

Planet’s orbital period is 90 daysPlanet’s rotation period is 60 days

A

B

C

D

Planet’s orbital period is 200 daysPlanet’s rotation period is 200 days (retrograde)

A

B

C

D

• Animation

?

?

Observations• Observing Mercury

– What are best conditions to observe• Unusual spin

– How suspected to be unusual– Why unusual– How verified– How to make a guess that will make you famous

• Craters– How similar to the moon– How different

• Unexpected magnetic field– Why unexpected– How measured

• Heavily cratered surface

• Less dense cratering than moon

• Gently rolling plains

• Scarps• No

evidence of tectonics

Note how much more densely the craters occur on the moon’s surface.

Scarps are cliffs

This one is more than a km high

They probably formed as the planet cooled and shrank

Animation

• The Caloris Basin is evidence of a large impact

The seismic waves from the impact that caused the Caloris Basin caused this deformation on the opposite side of Mercury

Observations• Observing Mercury

– What are best conditions to observe• Unusual spin

– How suspected to be unusual– Why unusual– How verified– How to make a guess that will make you famous

• Craters– How similar to the moon– How different

• Unexpected magnetic field– Why unexpected– How measured

Questions

• It is relatively difficult to observe details on the surface of Mercury from Earth because– A) detail is obscured by bright glows from hot

regions of molten surface heated by the intense sunlight.

– B) its orbit always keeps it on the opposite side of the Sun from Earth.

– C) it is a small object that always appears close to the Sun in the sky.

– D) its surface is always completely covered in clouds.

Questions• The reason the temperature on the dark side of

Mercury is warmer than originally expected is that– A) Mercury's large iron core conducts heat through

the planet.– B) Mercury does not rotate synchronously with its

orbital period.– C) several very active volcanoes on Mercury,

produced by tidal stresses from the Sun, produce excess heat.

– D) winds in Mercury's tenuous atmosphere carry heat from the daytime side to the night side.

Questions

• What is believed to be the cause of the long, meandering scarps (cliffs) observed on Mercury?– A) shrinkage of the planet as Mercury cooled– B) large impacts near the end of the early

period of heavy bombardment– C) volcanic eruptions along crustal faults over

hot spots in the mantle– D) crustal movement due to convection in the

mantle, similar to continental drift on Earth but to a much smaller extent

Outline For Today• Discuss Quiz

• Mercury

• Venus

• Mars

Interesting facts

• Mariner 2 visited in 1962

• Venus Express – recently arrived

Observations• Observing Venus

– What are best conditions to observe?• Unusual spin

– How suspected to be unusual– Why unusual– How verified– How to make a guess that will make you famous

• Craters– How similar to the moon– How different

• Unexpected magnetic field– Why unexpected– How measured

Observations• Observing Venus

– What are best conditions to observe?

• Unusual spin– How suspected to be unusual– Why unusual– How verified– How to make a guess that will make you famous

• Climate– Runaway greenhouse effect

• Surface

Venus’s rotation is slow and retrograde (“retro”)

No-name rotation

synchronous rotation

Mercury’s orbital period is 88 daysMercury’s rotation period is 58 days

A

B

C

D

88/4 = 22 days to get to A

0.375 of a turn

0.75 of a full turn

1.125 turns

1.5 turns

A

Venus’s orbital period is 224 daysVenus’s rotation period is 243 days (retrograde)

A

B

C

D

Draw ball and arrow at A, B, C, D

How long is Venus’s day?

Observations• Observing Venus

– What are best conditions to observe?

• Unusual spin– How suspected to be unusual– Why unusual– How verified– How to make a guess that will make you famous

• Surface• Climate

– Runaway greenhouse effect

The surface of Venus shows no evidence of plate tectonics

• The surface of Venus is surprisingly flat, mostly covered with gently rolling hills

• There are a few major highlands and several large volcanoes

• The surface of Venus shows no evidence of the motion of large crustal plates, which plays a major role in shaping the Earth’s surface

Volcanic eruptions are probably responsible for Venus’s clouds

• Venus’s clouds consist of droplets of concentrated sulfuric acid

• Active volcanoes on Venus may be a continual source of this sulfurous material

Observations• Observing Venus

– What are best conditions to observe?

• Unusual spin– How suspected to be unusual– Why unusual– How verified– How to make a guess that will make you famous

• Surface• Climate

– Runaway greenhouse effect

Climate on Venus followed a different evolutionary path from that on Earth

• Venus’s high temperature is caused by the greenhouse effect, as the dense carbon dioxide atmosphere traps and retains energy from sunlight.

• The early atmosphere of Venus contained substantial amounts of water vapor

• This caused a runaway greenhouse effect that evaporated Venus’s oceans and drove carbon dioxide out of the rocks and into the atmosphere

Climate on Venus followed a different evolutionary path from that on Earth

• Almost all of the water vapor was eventually lost by the action of ultraviolet radiation on the upper atmosphere.

• The Earth has roughly as much carbon dioxide as Venus, but it has been dissolved in the Earth’s oceans and chemically bound into its rocks

Runaway Greenhouse Effect