Lecture 6 - Habitability

Question 1

What are the 3 requirements for habitability?

Answer 1

1) Source of mols to build living cells
2) Source of energy to fuel metabolism
3) Liquid medium for transporting and exchanging mols

Question 2

What are the differences between Mercury and the Moon?

Answer 2

Moon:

• Orbits Earth in 27 days
• Tidally locked rotation (Day/Night 14 days each)
• Orbits sun in 365.25 days
• Made of light rocks similar to Earth crust

Mercury:

• Rotates slowly (59 days)
• Orbits sun fast and long days/nights (Each 88 days)
• Made of heavy, metallic rocks (like core), generating magnetic field

Question 3

How long does it take for Venus to orbit the sun?

What is weird about Venus’ rotation?

Answer 3

Sun orbit: 225 days
Rotation: 243 days
- Retrogade (opposite direction from other planets), maybe because planetismal hit it and changed its direction

Question 4

How far away is Venus from the sun? How much stronger does that make the illumination compared to the sun?

Answer 4

0. 72 AU from sun

1. 9x stronger than Earth

Question 5

How was radar reflectivity used on Venus?

Answer 5

By timing the intensity of radio signals as they bounce back from Venus, it can penetrate the thick clouds and map the surface

Question 6

Is there water on Venus? How is its atmosphere like?

Answer 6

No water (only 1/10,000th of Earth’s water)
Mainly CO2 atmosphere, dense. Similar CO2 content as Earth but most are in atmosphere instead of in the mantle and oceans

Question 7

Explain Venus’s runaway greenhouse effect.

Answer 7

High temperature increases evaporation, and warmer air holds more water vapour.
Causes positive feedback loop where additional water vapour strengthens greenhouse effect.

Result: Oceans evaporate and carbonate rocks decompose, releasing CO2 in atmosphere and strengthening effect more

Question 8

What happened to the H2O molecules on Venus?

Answer 8

Solar UV light split them
H escaped into space
O was either stripped by solar wind or oxidized into rocks

Question 9

How could we terraform Venus to be more habitable?

Answer 9

Bring A LOT of water
Remove A LOT of CO2 from the atmosphere
Absorb chemically active gases (SO2)
Establish an auto-regulation system for temperature

Question 10

Explain the properties of stars:
Mass
Luminosity
Lifetime
Surface temperature 
Radius

Answer 10

Mass: Constant throughout life but may lose material towards end

Luminosity: Brightness of star; Can change as inner structure changes

Lifetime: Depends on mass (amount of fuel) and luminosity (rate of fuel usage)

Surface temp: Depends on luminosity and size. Determined how energetic photons are that are radiated by its surface

Radius: Changes drastically during late-live evolution

Question 11

What are the properties of high mass stars according to the Stellar Main-Sequence (MS)?

Answer 11

They have:

• High MS temp
• High MS luminosity
• Shorter lifetime

Question 12

Which spectral type stars can support life?
O and B
A and F
G and K
M

Answer 12

O and B - No. Die too quickly
A and F - Maybe. Strong UV radiation and stellar lifetimes may be just barely too short.
G and K - Yes. Long lifetime. We orbit a G star.
M - Maybe. Most stars are M but can have trouble with tidal locking, stellar flares and small habitable zones

Question 13

What happens to the sun and its habitable zone when it becomes a red giant in ~5 Gyr from now?

Answer 13

It sheds its outer layers ad a planetary nebula
The HZ will extend past the Earth
Former core of sun (white dwarf) will dim and faint (will not provide enough energy for life anywhere)

Question 14

What binary star systems can work?

Answer 14

If 2/3 bodies are close to each other and the 3rd is farther away
If all 3 too close to each other, planet might get consumed or ejected