1. Direct Methods for Finding Exoplanets
21 October 2016

2. What is a planet? Does not shine by its own light
Too small to burn hydrogen (or even deuterium) by nuclear fusion
Forms from a disk around a star, not a multiple star

3. How to detect a planet Directly Indirectly
Reflected light from the star
Emitted light from the planet
Indirectly
Absorbs or blocks light
Refracts (bends) light
Changes the motion of nearby objects by gravity

4. Reflected light
Like Moon, Venus, Jupiter: even visible in daylight on Earth, if you know where to look
Necessary
Enough reflected light: decreases as square of distance
Separation of star and planet: angular separation of a distant object
Telescope resolution: capability to see two nearby objects: increases with telescope size
Sensitivity to see dim object near bright star: biggest problem

5. Emitted vs reflected light
Brightness increases with temperature
But wavelength of brightest emission decreases with temperature: hotter stars are more blue, cooler objects are redder
Go long! (look for planets at longer wavelengths)

9. 4 planets

13. Sunshade idea is under development at CU

14. Summary: Direct Methods
In principle, it is possible to see exoplanets by the light they reflect, but the brightness difference is too large: like a moth in a searchlight. Only a few cases found…
Infra-red light (IR) is more promising, because the planets are only a million times dimmer
Shades, coronagraphs, adaptive optics, interferometry improve this
Next time: indirect methods