Extrasolar planets Detection and habitability October 23rd 2014
Detecting exoplanets Primary methods : Direct imaging Transit Radial velocity
Direct imaging Planets are much fainter than their host star since they do not emit their own light By blocking the light from the star, it can be possible to reveal planets
Transit Looking at the planetary system from the side The passage of the planet create a very small dip in the luminosity of the star
Transit Looking at the planetary system from the side The passage of the planet create a very small dip in the luminosity of the star
Transit Looking at the planetary system from the side The passage of the planet create a very small dip in the luminosity of the star
Transit Looking at the planetary system from the side The passage of the planet create a very small dip in the luminosity of the star
Transit What other factor could influence the shape of the light curve? The size and period of the transiting planet
Radial velocity Gravity means that the star is pulling on the planet, but the planet is also pulling on the star This results in both going back and forth around their mutual center of gravity This change in speed means the spectral lines from the star are going to vary due to Doppler shift if there s a planet The more massive the planet, the larger the effect
In the lab Using real transit and radial velocity data taken at UVic, you re going to estimate the parameters for HD209458b Figure 9: The modeling program.
Habitable zone Suppose that all life needs liquid water There is only a certain zone not to close and not to far from the host star where liquid water is possible This is the habitable zone
Habitable zone The temperature of the star is a factor that influence how far this zone is going to be Which is going to have a closer habitable zone, a red or a blue star? The other important factor is the presence of an atmosphere to store heat and warm the surface through greenhouse effect
Thermal equilibrium On medium timescale, Earth s average temperature is not changing (longer than day to day, but shorter than global warming) The Earth is in thermal equilibrium with its environment Energyabsorbed = Energyradiated
Blackbody temperature A blackbody absorbs all incoming light and reemits the energy as a continuum spectrum The blackbody spectrum varies depending of its thermal equilibrium temperature (think of red vs. blue stars)
Albedo Surface Typical albedo Real objects or planets like the Earth are not perfect blackbody, they reflect some of the incoming light The fraction of reflected light is called albedo. It is 0.4 (or 40%) for the Earth. In other words, the Earth absorbs 60% of the incoming light Fresh asphalt 0.04 Worn asphalt 0.12 Conifer forest 0.10 Bare soil 0.17 Green grass 0.25 Desert sand 0.40 Ocean ice 0.6 Fresh snow 0.85
Blackbody temperature A planet twice the distance from the Sun receives 4 times less light (4πr 2 ) A fraction of the light is reflected The energy absorbed is going to bring the planet to its thermal equilibrium temperature or blackbody temperature FL 1/4 T BB = AD 2
Greenhouse effect Ein = Eout Ein (surface) = Eout (surface) Atmosphere absorb IR but let visible light through Eatm = Eout (surface) Ein (surface) = Eout (surface) = Esun + 0.5 x Eatm Ein (surface) = 2 x Esun
Greenhouse effect Ein = Eout Simply by adding an atmosphere that absorbs the IR emitted by the surface, we double the energy the surface actually absorbs T w/ atm = (2) 1/4 T BB 1.19 T BB
In the lab One bottle filled with air, one filled with CO2 100% CO2 (most thermal radiation captured by CO2) AIR (most thermal radiation escapes) The black cardboard serves as our blackbody surface, absorbing visible light and emitting IR thermometer thermal radiation visible light visible light thermal radiation thermometer Should we see a difference in temperature? What do you predict? Light source Light absorbers (black paper)