Section 4. Terrestrial planets

Question 1

What is the expected temperature of Mercury?

Answer 1

436K

Question 2

What is the basic description of Mercury?

Answer 2

Heavy cratering
High density
Weak magnetic field
Slow rotation

Question 3

What is the expected temperature of Venus?

Answer 3

230K

Question 4

What is the basic description of Venus?

Answer 4

Thick CO₂ atmosphere
735K on surface
Slow rotation
High albedo 0.8
Young surface covered in volcanic craters

Question 5

Do Mercury and Venus have moons?

Answer 5

No

Question 6

What is the expected temperature for Earth?

Answer 6

255K

Question 7

What is the basic description of Earth?

Answer 7

Thinner N₂ atmosphere
Strong magnetic field
Liquid water and life
Only planet with plate tectonics
Very young surface

Question 8

What is the expected temperature for Mars?

Answer 8

189K

Question 9

What is the basic description of Mars?

Answer 9

Lower mass and density compared to Venus/Earth
Red iron oxide surface
Evidence of water in the past

Question 10

Why does Mars have a lower surface temeprature?

Answer 10

Very thin CO₂ atmosphere and very little greenhouse and poor het redistribution

Question 11

How many moons do the Earth and Mars have?

Answer 11

Earth: 1
Mars: 2

Question 12

How old are the surfaces of the terrestrial planets?

Answer 12

Mercury: 4.5 Gyr
Venus: 1 Gyr
Mars: 2 Gyr

Question 13

What are the layers if the Earth?

Answer 13

Iron core
Silicate mantle
Curst of lighter minerals

Question 14

What are the types of seismology waves?

Answer 14

P-waves( pressure: solids and liquids)
S-waves( shear: only in solids)

Question 15

What is a refractory compound?

Answer 15

Solid at high temperatures

Question 16

Why does the Earth’s interior remain hot?

Answer 16

Radioactivity
Heat flux ~0.1Wm^-2

Question 17

How is the Earth’s magnetic field generated?

Answer 17

By a magnetic dynamo
(Requires a conducting medium, rotation and convection)

Question 18

How often do the poles on the Earth reverse?

Answer 18

~0.5 Myr

Question 19

What is the timescale for cooling?

Answer 19

τ_cool α surface area / volume α 1/R

Question 20

What does Lunar seismology show?

Answer 20

A thicker lithosphere and small molten core
No global magnetic field but evidence of dynamos in the past

Question 21

What do detections of Mars quakes show?

Answer 21

Thicker lithosphere and molten core
No magnetic field but evidence of dynamos in the past

Question 22

Why might Mercury have a weak magnetic field?

Answer 22

High density and oversized iron core
Tidal heating

Question 23

What is the equation for the half life?

Answer 23

λ = ln2/τ_1/2

Question 24

Why does Mars have the largest volcanoes?

Answer 24

The plates don’t move across the mantle plumes

Question 25

Why does Venus not have volcanoes?

Answer 25

Lithosphere too thin to support such large volcanoes Pancake domes and coronae when volcanoes collapse under their own weight

Question 26

What is the description of Earth's atmosphere?

Answer 26

1 bar 80% N 20% O₂ 33K between surface and equilibrium

Question 27

What is the description of Mars atmosphere?

Answer 27

0.006 bar 95% CO_{2 3% N Surface temperature varies on day/night and seasons}

Question 28

What is the description of Venus atmosphere?

Answer 28

93 bar 96% CO₂ 4% N 505K difference between equilibrium and surface due to very strong greenhouse

Question 29

Why does the Moon and Mercury not have atmospehres?

Answer 29

Surface gravity is too low to retain a significant atmosphere

Question 30

What is the equation linking surface temperature to equilibrium temperature?

Answer 30

T_S⁴=(1+3/4 τ) T_P⁴ Where τ is the optical depth

Question 31

What is the equation for intensity through a material?

Answer 31

I=I₀e^-τZ Where τ is the optical depth

Question 32

Why are the atmospheres of Earth and Venus so different?

Answer 32

Earth has a negative feedback in carbon silicate cycle Venus has a positive feedback loop led runaway greenhouse effect

Question 33

What happened to the water on Venus?

Answer 33

Split by UV photolysis into hydrogen and oxygen Supported by large large areas of deuterium

Question 34

What is the equation for mass loss rate?

Answer 34

ṁ ≤ L_xR_P³/4GM_Pa²

Question 35

How is the water on Earth protected from photolysis?

Answer 35

By the ozone layer and trapped trapped lower in atmosphere as it condenses into clouds

Question 36

Which of the terrestrial planets is the most eccentric?

Answer 36

Mercury

Question 37

How do the terrestrial planets rotate?

Answer 37

Earth and Mars rotate rapidly Venus and Mercury rotate very slowly

Question 38

What is the equation for sidereal day?

Answer 38

1/P_solar=1/P_spin-1/P_orb

Question 39

What are the spin obliquities of Mercury and Venus?

Answer 39

Very small due to tidal synchronisation

Question 40

What are the spin obliquities of Earth and Mars?

Answer 40

23 degrees Causes seasons

Question 41

What is the Roche limit?

Answer 41

The limit to orbital separation where self gravity is smaller than the differential gravity from the planet?

Question 42

What is the equation for the Roche limit?

Answer 42

a_R³=2R_m³M_p/M_m

Question 43

Why do Mercury and Venus have no moons?

Answer 43

Slow rotation means that any moon within their Hill spheres would spiral in and be destroyed at the Roche limit