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Life in the Cosmos > Exoplanets part 1 > Flashcards

Exoplanets part 1 Flashcards

1
Q

Why are exoplanets difficult to observe?

A
  • Don’t produce any light of their own
  • Incredibly distant
  • Millions times dimmer than the stars they orbit
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2
Q

What are the two ways to search for exoplanets?

A

Directly - pictures or spectra for direct evidence
Indirectly - precise measurements of a star’s properties may reveal effects of orbiting planets

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3
Q

When does direct detection work?

A

Star system is near
Planet is large
Large distance from host tar
Planet is hot

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4
Q

What are the 5 indirect techniques used?

A

Astronomy
Transits
Doppler shifts
Pulsar timing
Microlensing

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5
Q

What is the astronomy technique?

A

Observe motion of stars across the sky

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6
Q

What is the basis for the astronomy technique?

A

All stars exhibit proper motion with most being small (5-10 km/s) compared to galactic rotation of 250km/s.
Nearby stars change their position by a few arcsec per year

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7
Q

How does the astronomy technique work?

A

If planets going around a star, the stars proper motion changes

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8
Q

What causes modification of stars proper motion?

A

Gravitational pull of planet

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9
Q

What example can be found of greatest proper motion?

A

Barnards star has motion of 10 arcsec/yr
Very near to us

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10
Q

What is the Planetary transits technique?

A

Planets crossing stars and dimming them

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11
Q

How does Planetary transit technique work?

A
  • Earthlike planets dims sunlike star by hundredth of a percent
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12
Q

What can Planetary transits tell us?

A
  • How often this happens give us orbital period
  • Duration, depth and shape give indicators of planet/star size ration
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13
Q

How would Planetary transit look like for our solar system?

A

Jupiter would cause dimming of 1% every 12 years
Transit of Earth would cause 1/12000 drop

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14
Q

What are the problems with using transits?

A
  • signal drop can be very small
  • dont know when it will happen
  • Some orbital periods are very long
  • high rate of false detections
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15
Q

How does the transit method allow a planets atmosphere to be studied?

A

Analyse light passing through its upper atmosphere and study stellar spectrum

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16
Q

What has the Kelper mission found?

A

9.6 yrs in orbit
Discovery of 2,600 planets
Observed 500,000 stars

17
Q

What is the Doppler shift technique?

A

Looking at stars orbital movement around its centre of mass by studying its spectrum.

18
Q

How does the Doppler shift technique work?

A

Small shifts in wavelength are caused by velocity changes of star as planets go around it

19
Q

Where is the centre of mass between the sun and Earth?

A

333,000 times closer to the centre of the sun than the Earth.

20
Q

How does sun and earth orbit each other?

A

Earth moves at 30km/s around its orbit. Sun moves at 1/330,000 so 10cm/s around its orbit.
Jupiter causes 30m/s

21
Q

What are the limits for doppler method?

A
  • Best suited for identifying massive planets close to host star
  • detection limit is 1m/s
22
Q

What was the exoplanet discovery in 1995?

A

51 Pegasi - sunlike star
Dimidium planet - close to star
- surface temp 1200
- mass half of jupiter

23
Q

What is the Pulsar Timing Technique?

A

Using cosmic clock to reveal planets?

24
Q

How has Pulsar Timing worked?

A

PSR 1257+12 neutron star spinning at 161 times per second
Observe modulation due to presence of planets in this clock frequencty

25
Q

Limitations to Pulsar Timing

A

Only find planets around dead stars

26
Q

How does gravitation microlensing technique work?

A

Light from a distant object will bend due to the distortion of space

27
Q

What will a planet do to light beams?

A

Focus them and cause increase in brightness

28
Q

What is the chance of planet causing lensing effect annually?

A

1 in a million

29
Q

What is the Optical Gravitational Lens experiment in Chile?

A

Polish project to discover dark matter using microlensing technique

30
Q

What does OGLE do?

A

Observes several million stars each night
17 planets discovered

31
Q

What are the problems with gravitational lensing?

A

Never predict where it will happen
Can never repeat the experiment

32
Q

What is Barnards star?

A

Red dwarf of spectral type M4

33
Q

What is the first confirmed transiting exoplanet?

A

HD209458

34
Q

How was 51 Pegasi found?

A

Doppler technique

Life in the Cosmos (18 decks)

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