Finding an Earth-like planet Flashcards
Why is direct detection difficult?
Glare of the host sun (Earth is 10^9 fainter)
What are Kepler’s 3 laws?
- orbits are ellipses with the Sun at one focus
- orbits trace out equal areas in equal times
- square of period = cube of distance
What is Doppler’s wobble effect (Radial velocity data)?
Is a TIME effect: as the planet pulls the star around lines in the stellar spectrum move backwards and forwards in wavelength
What 3 things can be found from Doppler’s wobble effect?
- Distance of planet from star: (mass star + planet)P^2= a^3
- Velocity of the planet: v(planet) = 2(pi)a/P
- Mass: M(planet)/M(star) = v(star)/v(planet)
Why does the mass given by the Doppler wobble effect give the MINIMUM planet mass?
Planet is orbiting at an unknown angle to us
Why are certain planets such as hot Jupiters thought to have migrated inwards?
torque exerted by disc, after planet cores formed outside the snowline
For which types of planets is the Doppler wobble effect most effective?
Large planets, or planets with smaller objects (e.g can only detect earth like planet around ‘Sun’ if the orbit was much smaller)
However red dwarfs give hope for finding potential for liquid water
What is the planet transit method? Also, what criteria must a planet fulfill in order for it to be possible?
Photometry: detection by transits (eclipses) of planets giving the planet/star ratio
Limits: can only be used when planet is observed ‘edge-on’ (90 degree tilt) and so planet mass ambiguity is removed
How can transit data be used to identify an atmosphere?
Use spectroscopy to look at data and see if the planet looks bigger at certain wavelengths (atmosphere extends past its core)
Which size planet radii gives predominantly rocky planets?
Less than 1.6 earth radii
Why are larger planets usually less dense?
Possibly due to:
- Ice mantles?
- Primordial hydrogen-helium atmospheres?
How do luminosities usually scale for stars?
Fourth power of their mass
What does stellar lifetime depend on?
Fuel consumption depends on its luminosity, and only 10% of the stars mass is suitable fuel
Therefore lifetime = fuel supply/fuel consumption or inverse cube of mass
What are the inner and outer edges of the habitable zone defined by?
inner: H2O dissociated by sunlight and the atmosphere escapes in the form of Hydrogen
outer: CO2 clouds form and sunlight is reflected, cooling the planet down
What is the worldwide average Earth temperature?
287K
