W9b nature and evolution of habitability

Question 1

what are the essential prerequisites for life?

Answer 1

1. source of molecules to build living cells
2. source of energy to fuel metabolism
3. liquid medium for transporting and exchanging molecules

Question 2

Expand on the requirements for life

Answer 2

1. fulfilled nearly everywhere
2. for photosynthesis and surface temperature; distance from the central star
3. most strict; doesn’t have to be at planet’s surface

Question 3

what is important about spontaneous life creation and just supporting life brought from outside?

Answer 3

there is a difference

Question 4

what is the relation between mass and temperature, luminosity, and lifetime for main-sequence (MS) stars?

Answer 4

higher mass = higher luminosity, temp & shorter life

Question 5

what are the prospects of life for each spectral type (star)?

Answer 5

O+B = die too fast 
A+F = strong UV rad.
G+K = long lifetime, many stars- earth orbits G type star- GOOD 
M= 75% of all stars; possible issues with tidal locking, stellar flares, small habitable zone

Question 6

What does the size of the habitable zone around a star depend on?

Answer 6

properties of the central star

• big/small
• luminous/faint
• massive/light

diff properties as it ages

Question 7

If life is similar to that on Earth, a habitable zone (HZ) would be a volume where…

Answer 7

• temp are not too high or too low for life to exist
• water present as liquid
• diff to estimate

Question 8

what will happen to the sun at the end of its red giant phase?

Answer 8

it will shed its outer layer to become a planetary nebula

Question 9

The end of the Sun will be in about ..? Then what? What will be habitable at that time?

Answer 9

5 Gyr- leaves the main sequence

• then live for another 1 Gyr
• Moons of Jupiter and Saturn will be habitable- hv liquid water

Question 10

If the sun were born a cool K-type star…

Answer 10

Mercury and Venus would be in the habitable zone

Question 11

If the sun was an M-type star…

Answer 11

The HZ wouldn’t even include mercury and a closer planet would likely be tidally locked to the star

Question 12

A 3 body system is stable only if…?

Answer 12

two bodies orbit close to each other, with the third body much further away
OR
wide binary system

Question 13

systems with all orbits of comparable sizes in a 3 body system are…?

Answer 13

unstable and planet will be ejected