Spectroscopic search for life

Question 1

When is a star in ‘red shift’ and when is it in ‘blue shift’?

Answer 1

red shift - moving away

blue shift - moving towards

Question 2

What are the 3 types of habitable zones?

Answer 2

1. Circumstellar
2. Galactic
3. Cosmological

Question 3

Why does metallicity dictate the galactic habitable zone and what is it influenced by?

Answer 3

• Metal elements (higher than H and He because astronomers are weird like that) necessary to form planets with molten cores which produce plate tectonics, magnetic fields, and can retain an atmosphere to shield from UV
• Too little metals and you get hot jupiters which may clean out habitable planets in migration (assholes)
• Determined by star formation and supernovae rates

Question 4

State the 4 areas for star formation in the galaxy and their metallicity properties

Answer 4

1. Halo - oldest and metal poor
2. Bulge - large ranges of metallicity but there’s a lot of disruptive events, radiation and close encounters
3. Thin disk - Plenty of star formations and hence high metallicity
4. Thick disk - more metal poor than thin disk

Question 5

What are 3 sources of danger in the galaxy and their rate

Answer 5

1. Supernovae (deadly increase in radiation) - 1.5 Gyr
2. Gamma Ray Bursts (could cause DNA damage) - 2-4 Myr (but short lived)
3. Active Galactic Nuclei outbursts could damage ozone through higher particle and UV radiation, no frequency given

Question 6

What is the Galactic Habitable Age range?

Answer 6

Must be above 2 Gyr - time needed to have enough metals to build terrestrial planets
Must be below 20 Gyr - growth of structure ceases, slow star formation and lower internal heat from radioactive isotopes

Question 7

What is the strongest biosignature?

Answer 7

The presence of an oxidising and a reducing gas (e.g O2 and CO2)

Question 8

What are the pros and cons of using N2O, CH3Cl and DMS (dimethylchloride) as biosignatures?

Answer 8

pros: no known abiotic source of these gases
cons: are produced in really small abundances because they are from highly specialized evolutionary pathways like a specific signaling mechanism for one single organism

Question 9

What is a type I biosignature?

Answer 9

redox grandient energy extraction by-products based on thermodynamics such as CH4 or NH3
High possibility of a false positive as they are equally favourable for Geology

Question 10

What is a type II biosignature?

Answer 10

biomass building biproducts such as O2/O3 which require outside energy

Question 11

What is a type III biosignature?

Answer 11

secondary metabolic byproducts which are produced by life for functions such as defense, signaling or physiological control that do not require energy from the environment
low possibility for false positive but also low abundance

Question 12

What are the 2 habitability markers?

Answer 12

H2O (can produce O2 abiotically) and CO2 (greenhouse gas and food)

Question 13

What effect does near UV (NUV) and far UV (FUV) have on O3?

Answer 13

NUV - destroys ozone

FUV - creates ozone

Question 14

Name the star classifications in order of largest to smallest

Answer 14

F, G, K, M

Question 15

What are the levels of NUV and FUV on F stars and M stars?

Answer 15

F - High NUV low FUV

M - Low NUV high FUV

Question 16

Why may plants orbiting an M star be black and plants orbiting a F star be blue?

Answer 16

M - black to absorb as much light as possible

F - too much light, adapted to reflect a lot

Question 17

Which part of the global heat flow is IR and UV?

Answer 17

IR - Outgoing Longwave radiation

UV - Incoming solar radiation

Question 18

What percentage of the stars in our galaxy are M dwarfs? How many of them have a planet in the habitable zone?

Answer 18

75%

1 in 4 estimated to have a habitable zone planet

Question 19

Why are small M stars at an ‘advantage’ for transit data?

Answer 19

• Planets will make a deeper transit depth by percent

- Planets orbit more closely and so have a more frequent transit

Question 20

How long do M stars remain active?

Answer 20

Hot M stars - 1-2 Gyr

Cool M stars - 6-8 Gyr (note: Sun was active for 0.5 Gyr)

Question 21

List 6 common false positives O2/O3? Which are common in M dwarfs?

Answer 21

1. Desiccated planets
2. Super luminous pre-MS dwarf
3. Lack of cold trap
4. CO2 photolysis
5. Inner edge of the habitable zone
6. CO2 rich/H2 poor planets
   Common for M stars: 1, 2, 4, 6

Question 22

Describe the Super-luminous pre-MS M dwarf false positive scenario

Answer 22

• Extreme UV radiations breaks H2O down into H2 and O
• O2 atmosphere and H2 escapes to space leaving the planet permanently dry
  Note: similar for inner HZ scenario