1. Planets Elsewhere? Protoplanetary Disks and universality suggest many stars have planets First discovery in 1988. Now 853 around 672 stars Finding planets is tough: dim, small, near bright star. 32 planets in 28 systems detected by imaging 1

2. Who Orbits Whom? Planet and Star orbit common center of mass One detection by Astrometry 2

3. How Fast? 3 498 planet in 386 systems detected by radial velocity measurements

4. Transiting Planets If planet eclipses star can observe light curve Shape of curve helps find size, mass, even properties of atmosphere of planet 290 planets in 235 systems detected via transit Kepler has 2321 candidate planets in 1290 systems 4

5. Other Methods Gravitational lensing of starlight by planet. 16 planets in 15 systems Transit Timing Variation uses discrepancies in transit times of eclipsing planet to predict others in same system 5

6. What Have We Found? 1-40% of (Sunlike) stars have planets. Planets are ubiquitous! Our methods are most sensitive to hot Jupiters so these are mostly what we find Migration is common as are strongly interacting orbits 6

7. What Are They Like? Taking selection bias into account, super Earths outnumber Jupiters Some SuperJupiters Kepler-16b orbits two stars 7

8. The Sun Shines – but How? Sun is big and hot so luminous How does it stay hot? Chemical (rearrange electrons - electromagnetic) burning produces per atom, or per kg. Need to burn so run out in Kelvin-Helmholtz (gravitational) energy would last 8

9. Nuclear Physics Why don’t nuclei break up under electric repulsion? A strong attractive force binds nucleons Short-range since atoms do not collapse 9

10. Nuclear Energy Rearranging nucleons recover nuclear energy In large nuclei distant nucleons barely attract Breaking up – fission – or emission recover electromagnetic energy Heats planets powers reactors 10

11. Fusion? In small nuclei, less attractive interactions Liberate nuclear energy by fusion to Helium Problem: Hydrogen is all protons Strong interactions cannot change a proton to a neutron 11

12. Weak Interactions Something can do this! And the inverse A free neutron decays in 15min Weak nuclear force mediates this decay 12

13. Some Questions and Answers Can a force change one particle into another? Is a neutron just a tiny Hydrogen atom? What is ? Are there any rules? Conservation Laws – Mass-Energy – Momentum – Angular Momentum – Electric Charge – Electron Number Weak interaction: rare 13 Yes No

14. Particle Physics ParticleQNeNe 10 00 1 01 0 00 1 0 00 Antiparticle: same mass opposite charges Neutrinos almost massless, weakly interacting Discovered as missing energy in decay 14

15. Solar Energy p-p chain is source of Solar Energy Sun could last 15

16. What it Takes To initiate fusion, protons must overcome electric repulsion One proton must inverse decay before highly unstable breaks up Requires temperatures of - only in core Inefficient because weak process required 16

17. How Do We Know? Theory (Eddington, Bethe 1932) first Davis, Bahcall (1968): Detect the Pro: Penetrate Sun Con: Penetrate detector Flux at Earth: Put a tank with of Chlorine in Homestake Gold Mine Requires high-energy produced in other processes Expect one atom per six days 17

18. Where Are the Neutrinos? Flux Found is less than predictions Is Solar Model wrong? Is detector model wrong? Decided in 2001 by SNO: particle physics 18

19. More Particles, More Charges ParticleQNeNe NμNμ NτNτ Mass 1000935 0000938 1000.511 0100? 010106 0010? 0011777 0001? 19

20. So What? Neutrinos change spontaneously en route pp process produces When they arrive, 1/3 are This implies, in particular, that neutrinos are not massless although light. 20