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

2

Who Orbits Whom?• Planet and Star orbit common center of mass

• One detection by Astrometry

3

How Fast?

• 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

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

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

7

What Are They Like?• Taking selection bias

into account, super Earths outnumber Jupiters

• Some SuperJupiters• Kepler-16b orbits two

stars

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

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

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

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

12

Weak Interactions• Something can do this!• And the inverse• A free neutron decays in

15min • Weak nuclear force

mediates this decay

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

Yes

No

14

Particle PhysicsParticle Q Ne

1 0

0 0

-1 1

0 1

-1 0

0 0

1 -1

0 -1

0 0

• Antiparticle: same mass opposite charges

• Neutrinos almost massless, weakly interacting

• Discovered as missing energy in decay

15

Solar Energy• p-p chain is source of Solar

Energy

• Sun could last

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

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

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

19

More Particles, More ChargesParticle Q Ne Nμ Nτ Mass

1 0 0 0 935

0 0 0 0 938

-1 1 0 0 0.511

0 1 0 0 ?

-1 0 1 0 106

0 0 1 0 ?

-1 0 0 1 1777

0 0 0 1 ?

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.