Week 3: Habitability

Question 1

How does the element composition of biological objects compare to nonbiological objects like stars and planets?

Answer 1

carbon, nitrogen, and oxygen are 300x more common in biological objects than in the rest of the universe

Question 2

When were light elements (hydrogen, helium, lithuim) formed?

Answer 2

first three minutes of big bang
helium is created from hydrogen in stars

Question 3

What kinds of elements can low mass stars fuse in their cores?

Answer 3

helium, carbon

Question 4

What kinds of elements can high mass stars fuse in their cores?

Answer 4

heavier elements up to iron

Question 5

Why is iron the upper limit for what elements can be fused inside of stars?

Answer 5

it is super stable
conditions to fuse it need to be really extreme, like supernovae

Question 6

Why is carbon relatively rare in the universe?

Answer 6

fusion of carbon in stars relies on the triple fusion between 3 He nuclei, which is a rare occurrence

Question 7

Why can larger stars fuse heavier elements?

Answer 7

heavier elements need higher temperatures and pressures to fuse

Question 8

How are stars layered?

Answer 8

the closer to the core you get, the hotter and more pressure there is -> heavier elements can form
lighter elements fuse on outer layers of star, heavier elements fuse closer to core
core is made of iron in a plasma state due to the crazy high pressure

Question 9

How do stars disperse the materials they fuse throughout the universe?

Answer 9

when a star gets old, it becomes unstable and ejects some matter into space
a star dies when it can’t fuse and its core collapses -> supernova, where an explosion distributes matter into space

Question 10

True or false: since stars fuse elements in different layers, when they eject material only lighter elements on the outer layers are ejected.

Answer 10

false - stars have convection, so the ejected material contains a mix of elements

Question 11

what is explosive nucleosynthesis?

Answer 11

process by which heavy elements are spontaneously created during a supernova explosion

Question 12

How is the interstellar medium changing over time?

Answer 12

as more stars fuse heavier elements and release them into the interstellar medium, it is being enriched with these elements over time

Question 13

what two main ingredients are critical for earth biology?

Answer 13

water and carbon

Question 14

why is water so important for earth biology?

Answer 14

used by almost every earth organism
life on earth began in water
good at facilitating biological processes (ex. nutrient transfer, waste elimination)
solvent required for many chemical reactions

Question 15

what four elements make up the majority of the human body? rank them in order of amount. what percentage of the body do these elements together make up?

Answer 15

oxygen
carbon
hydrogen
nitrogen
96%

Question 16

what is an organic molecule?

Answer 16

made of carbon bonded with hydrogen
basis of biological life

Question 17

true or false: organic molecules are exclusively created on earth

Answer 17

false
we have found some in space that were probably created there

Question 18

what is the significance of the murchison meterorite?

Answer 18

came to earth in 1969
landed in desert area -> minimal contamination from earth stuff
contained a bunch of complex organic molecules that formed in space

Question 19

what is the traditional definition of the habitable zone?

Answer 19

range of distances from a star where water on the surface of a planet or moon can be liquid (surface temperature between 0C and 100C)

Question 20

What possibilities are not accounted for by the traditional definition of the habitable zone?

Answer 20

properties of the exoplanet
different requirements for life
life might not be on the planet’s surface

Question 21

How does a star’s type impact its planets abilities to have life?

Answer 21

larger stars -> shorter lifespans -> maybe less of a chance for life to form there
size of star also impacts at what distances liquid water can form on the planets’ surface

Question 22

true or false: planets close to a star receive more light

Answer 22

true
star rays are spread out evenly as they travel away from the star
closer to the star, rays are closer together, so more light is received per unit of area

Question 23

What two properties of exoplanets could impact whether or not they can have liquid water on their surfaces?

Answer 23

if large enough to be geologically active, an exoplanet could produce some of its own heat (volcanic activity or radioactive decay)
if large enough to have a thick atmosphere, it could increase surface temperatures and pressures

Question 24

what is notable about TRAPPIST-1?

Answer 24

system 39 light years away
has 7 terrestrial planets, 3 of which are within habitable zone

Question 25

What letters are used to represent the spectral types of stars? Name them in order and describe what the order indicates.

Answer 25

M K G F A B O
smallest -> largest

Question 26

What determines a star’s spectral type? What other information can we gather from this?

Answer 26

its mass
how hot it is (larger = hotter)
how luminous it is (larger = more luminous)
what color it is (larger = bluer, smaller = redder)

Question 27

True or false: The mass of a star determines all of its properties

Answer 27

true!!!!

Question 28

How does the mass of a star influence its central temperature and pressure?

Answer 28

larger stars = more gravitational influence on self = higher central temperature and pressure

Question 29

How does fusion impact a star’s pressure?

Answer 29

fusion makes pressure facing outwards from inside a star, which prevents the star from collapsing inwards

Question 30

How does mass indicate a star’s fusion rate? What does this say about its lifespan?

Answer 30

higher mass = higher central temperature and pressure = faster fusion rate = shorter lifespan (the star will fuse all of its fuel sooner and then die)

Question 31

Which star types are the best to look for life around? Why?

Answer 31

M, K, G, F
they are smaller and have larger lifespans
larger stars would die earlier and annihilate life on their planets

Question 32

How many stars form each year in the milky way that we would consider suitable for life to form around?

Answer 32

7

Question 33

How does the size of a star impact its traditional habitable zone?

Answer 33

larger stars have habitable zones further away from them and also wider, while smaller stars have smaller habitable zones

Question 34

What is luminosity? How is it measured?

Answer 34

total energy emitted by something (a star)
joules / second, watts

Question 35

Where does the luminosity of a star come from?

Answer 35

fusion reaction releases protons!!

Question 36

True or false: Since larger stars have larger habitable zones around them, large star systems make up most of the habitable areas in the universe.

Answer 36

its false!!
dwarf stars are wayyy more common than massive stars, so even though they have smaller habitable zones overall most habitable area in the universe is around them.

Question 37

What is the cryogenic biosphere? What 3 things does this idea account for that is not in the traditional habitable zone?

Answer 37

area beyond the traditional habitable zone that might still be habitable
accounts for a bunch of things:
- other hydrocarbons can potentially be liquid in regions beyond where water can be liquid
- exoplanets can be heated by atmospheric pressure or geologic activity
- possibility of subsurface liquid water

Question 38

How many habitable exoplanets is it estimated that every star has?

Answer 38

maybe like a couple?
based on estimation that each star has at least one exoplanet