Lecture 10 - Extra Solar Planets

Question 1

What is the Herzsprung-Russell (HR) diagram?

Answer 1

Used to categorize stars

Stars plotted by its luminosity (y-axis) and surface temp (x-axis)

Question 2

What are main sequence stars?

Answer 2

Stars currently burning hydrogen into helium

Stars spend 90% of their lives in main sequence

Question 3

What happens to a star at the end of its main sequence life?

Answer 3

1) Expansion
2) Loss of envelope (gentle or supernova)
3) Leaves a small hot core behind (white dwarf, neutron star or black hole)

Question 4

What are the 2 difficulties of finding extra solar planets?

Answer 4

1) Immense distance (Mainly empty space between stars too, low chance of collision)

2) Size and mass
Light reflecting from planet depends on its SA so it will only be a very tiny fraction of star’s light that we dee directly. Plus planet’s effect on motion of its star very tiny because mass much smaller.

Question 5

What were the first extrasolar planet discoveries in 1992 and 1995?

Answer 5

1) Wolszcan and Frail discovered three planets around a neutron star but it was strange
2) Mayor and Queloz discovered first planet orbiting solar-type star

Question 6

Describe the direct ways of finding extrasolar planets.

Answer 6

Direct imaging

• Take pic of a planet (preferable large, young and hot planets orbiting far from star)
• Difficult because planet is fainter far away from star

Question 7

Describe the indirect ways of of finding extrasolar planets.

Answer 7

1) Astrometry + Doppler technique
- Look for displacements where planets move around the centre of gravity
- If we view Face-on: Displacement
- If we view Edge-on: Displacement and motion toward (blue) or away (red) from Earth

2) Transit Technique
- Planet passes in front of star, brightness becomes dimmer

Question 8

What are the other ways to find extrasolar planets?

Answer 8

1) Gravitational lensing

2) Pulsar timing

Question 9

Why is there selection bias in finding extrasolar planets? (doppler technique)

Answer 9

1) We’re mainly only discovering the most massive and closest-orbiting planets using the Doppler technique because it’s easier to detect
2) Favour in edge-on systems because if face-on, no radial velocity variations will be detected

Question 10

What are hot Jupiters?

Answer 10

Gas-planet that formed in outer part of proto-planetary disks and migrated down

Question 11

What are the cons of direct imaging?

Answer 11

• Only for large, hot planets far from star

- Works for systems close to Earth

Question 12

What are the pros and cons of Doppler technique?

Answer 12

Pros:

• Sensitive to massive planets close to star
• Measures mass

Cons:

• Needs lots of telescope time per star
• Insensitive to small planets far from star
• Only edge-on systems
• Can’t tell radius or density of planet

Question 13

What are the pros and cons of transit technique?

Answer 13

Pros:

• Can also detect Earth-sized planets in HZ
• Can monitor many stars at once
• Measures orbit and radius, but mixed with Doppler technique can also give mass and density

Cons:

• Must use continuous monitoring
• Only edge-on systems

Question 14

What was the Kepler Mission?

Answer 14

Determine the freq of Earth-sized and larger planets in HZ of stars like ours
Determine size and orbital period distributions of planets

Question 15

What is the percentage of Earth-like planets in the Kepler mission?

Answer 15

17%

Question 16

How can we use spectra to determine if life is on a planet?

Answer 16

IR spectra detected for of oxygen, gaseous and liquid water and methane are biomarkers for life