Pulsar Timing Score = 33 How it works Pulsar sends out very regular signal Pulsar is slightly nearer/farther from us Pulses come slightly late/early Advantages Very sensitive Cheap See low mass planets Disadvantages Works only on pulsars (weird stars) Score = 33

Other Timing Score = 25? How it works There are other very regular signals from stars Orbiting eclipsing binary stars Pulsating subdwarf stars Signals come slightly late/early Advantages Can see planets with large orbits Disadvantages Works only in very special circumstances (rare) Score = 25?

Radial Velocity / Doppler Method How it works Star moves towards and away from us Alternating red-shift / blue shift Disadvantages Massive planets Small fast orbits No observation of planet Advantages Sensitive method Q. 60: Radial Velocity Method Score = 814

Transit Method Score = 2911 How it works Planet blocks light from star, making it dim Star blocks light from planet Disadvantages Requires Luck False Positives (requires confirmation) Advantages Works well from space Measure spectrum of planet Measure atmosphere of planet Score = 2911

Spacecraft for the Transit Method TESS Operating ’18–’30? Expect 20,000+ planets COROT Operated from ’08–’13 Kepler Operated ’09–’18 Has seen sub-Earth sized planets

Sub-Earth-Sized Planets from Kepler

Earth-Sized Planets Are Not Uncommon

Earth-Sized Planets in Habitable Zone

What Have We Learned? Many large planets – Jupiter size and greater Planets as small as Earth and smaller Observational bias favors finding large planets Often find planets very close to star Observational bias Gas giants can live very near their stars Orbits often highly eccentric

Lessons from Extrasolar Planets? We probably need to rethink our understanding of how stellar systems form Planetary migration is often an important factor? Giant planets form far away Later move inwards Eccentric and even retrograde planets are not rare Planets are not uncommon Including Earth-sized planets Stay tuned

End of Material for Test 2 Questions?

Magnetic Fields and Charged Particles The Sun Magnetic Fields and Charged Particles Charged particles are affected by magnetic fields They are forced to follow magnetic field lines Magnetic fields

Plasmas At ordinary temperatures, atomic nuclei attract electrons to make them neutral At extreme temperatures, the electrons pop loose, and the electrons can run off freely This is a plasma Plasmas are excellent conductors They can generate magnetic fields

Atomic Spectra Suppose you take an atom and bump the electrons up (by heating it, for example). What type of light comes out? Spectrum consists of emission lines Exactly which lines tells you the kind of atom, like a fingerprint

Atomic Spectra Suppose you take an atom and shine a bright white light on it. What does the spectrum of the light look like when it comes out? Initial spectrum is continuous Atom absorbs certain very specific frequencies The same frequencies you saw before.

Kirchoff’s Laws Hot thick solid, liquid, or gas – Continuous spectrum Thin gas – bright line spectrum Thin gas with hotter thick gas behind it – dark line spectrum

Kirchoff’s Laws Continuous Spectrum: Hot, thick solid, liquid, or gas Bright Line Spectrum: Hot, thin gas Dark Line Spectrum: Cooler gas in front of hot, thick solid, liquid, or gas

Stellar Spectra Q. 61 Simple Stellar Spectrum Q. 62: Complicated Stellar Spectrum

The Sun’s Spectrum Hundreds of lines Scores of Elements

Composition of a Typical Star (Sun) Hydrogen Helium Oxygen Carbon Iron Neon Sulfur Nitrogen Silicon Etc. Know These!

The Sun: Basic Facts March 1, 2019 from SDO 109  Earth diameter 333,000  Earth mass Density: a bit higher than water Rotates once every 25 days Differential rotation

The Sun: How We Know What We Know Exterior Spectra Temperature Motion Chemical Composition Magnetic Fields Ground-based telescopes Eclipses Space telescopes Solar Wind Interior Gravity Magnetic Fields Neutrinos Helioseismology

Solar Dedicated Spacecraft Solar Dynamics Observatory STEREO SOHO IRIS

More Solar Dedicated Spacecraft Advanced Composition Explorer Hinode Parker Solar Probe DSCOVR