Extra-Solar Planets Astronomy 311 Professor Lee Carkner Lecture 24

How is energy transported from the core of the sun to the Earth? a)By radiation b)By convection c)By convection then radiation d)By radiation, then convection, then radiation again e)By conduction

What causes the 11 year sunspot cycle? a)The 11 year convection cycle b)The 11 year orbit of Jupiter c)The 11 year winding of the magnetic field d)The 11 year proton-proton cycle e)The 11 year coronal mass ejection cycle

End of Semester  Observing project due Friday  Should be neat, legible and organized  Answer questions on a separate sheet of paper  Final exam Monday, 3 pm

Finding Exoplanets  How do you find a planet around another star?  Planets are much too faint to be seen with a telescope   As the planet orbits the star, the star also orbits the planet   The motion of the star is quite small, but can be detected as a slight shift in the spectral lines of the star

Finding Exoplanets

The Doppler Effect  When you observe a moving object, the wavelengths of light you observe change   Moving towards -- wavelength decreases -- blue shift  Example:  The faster the motion the larger the change  By measuring the shift of lines in a spectrum, you can determine how fast the object is moving

Doppler Effect

Searching For Exoplanets   Measurements are made over a long period of time and plotted   As the star moves around in its orbit the velocity should go from positive to zero to negative and back to positive again   We find exoplanets by noticing changes in the spectral lines that indicate a planet tugging on the star

Inducing Stellar Motion

Orbits of a Star+Planet System Star Planet Center of Mass V star V planet

Light Curve of 51 Peg

Planetary Properties   Use Kepler’s 3rd Law (P 2 =a 3 )   Larger planets produce a larger velocity   Large velocities and short periods are easier to measure

What is a Planet?  Star --  Mass > 0.08 M Sun (84 M Jupiter )  Brown Dwarf --  Mass > 10 M Jupiter  Planet --  Mass < 10 M Jupiter  Planets and brown dwarfs can be hard to tell apart

Known Exoplanets  About 250 exoplanets are known   Masses range from  Orbits range from  Searches are biased towards large planets in tight orbits

Sample Exoplanets Data

Exoplanet Orbits   Most systems have only one known planet but we are starting to find more   Long term observations are needed to see the longer periods   Are the mostly circular orbits of our solar system atypical?

Velocity Plots for Upsilon And System

Orbits in Upsilon And System

A Multiple Exoplanet System

Orbit Evolution  How do you get a large planet in a close orbit?   Not enough material to form a large core   The magnetic field of the star may produce a “hole” in the inner disk, stopping the motion before the planet hits the star

Exoplanets and Habitability  Are any of the new planets habitable?  No,   They are almost all gas giants with no surface  However,   Example: 47 UMa, R orbit =2.1 AU   The velocities they produce are too small to measured via Doppler shift

Transits   For orbits seen edge on, the planet passes in front of the star once per orbit   We can measure and time this slight dimming with CCD cameras  By measuring the degree and length of the dimming the size and orbit of the planet can be found

Transit Light Curve

Space Interferometry  One idea to find low mass planets is with an interferometer   A two telescope, Space Interferometry mission (SIM) may be launched in 2015 (?)   Would be able to detect the movement of a star in the sky as it is being pulled by its planets (astrometry)   Very large interferometers could take spectra of planets to look for signs of life

Planetary Spectra

Next Time  Read Chapter 28

Summary  Recently many planets around other stars have been found  The planets are detected by measuring the motions they induce in the central star  The period and velocity of the motions allows the determination of the mass and orbit of the planet  New missions in the next 20 years will allow for the detection of many new planets, including Earth-like, habitable ones

Summary: Exoplanet Properties  Most known exoplanets are large (~M Jupiter ) and in close orbits  They may form further out and then move in  A few are near the habitable zone  We are starting to find additional planets in the systems