EXAM II COMING UP Monday Oct 19 th (a week from this coming Monday!) HW5 due a week from today

Other solar systems (Exoplanets)

How are they found? Most straightforward: Direct imaging (in infrared) This method works best for Big, young planets that emit infrared light and are Far from the glare of the star. Systems must be fairly near to Earth

(Keck) DISTANCE: 128 light-years HR8799 ~5 M J 68 AU ~7 M J 24 AU Recall Jupiter’s orbit is 5.2 AU

170 light-years ~4 M J 41 AU

DISTANCE: ~500 light-years ~ 35(?) M J ~ 114 AU GQ Lupi b

How are they found? Less straightforward: Indirect methods Astrometric measurements Velocity curves Transits

The wobbly-star method: Astrometric measurements Velocity curves

Recall the mutual orbits of two masses of similar size

center of mass MSMS MPMP a Circular orbit example

center of mass MSMS MPMP a

If we can “see” the star’s wobble i.e. measure P and R S Then we can infer a and M P

Astrometric method – measure the star’s wobble directly The claim: Jupiter-sized planet Discredited ! only 6 ly away GAIA up and running – no exoplanet results yet (primary mission is parallax measurements)

Slightly bluer light Slightly redder light HH Doppler shift method (radial velocity method)

To Earth Radial velocity 0 Doppler shift only measures the radial velocity (i.e. velocity component along the line-of-sight to earth)

To Earth Radial velocity Doppler shift only measures the radial velocity (i.e. velocity component along the line-of-sight to earth)

To Earth Radial velocity = V max Doppler shift only measures the radial velocity (i.e. velocity component along the line-of-sight to earth)

To Earth Radial velocity = 0 Doppler shift only measures the radial velocity (i.e. velocity component along the line-of-sight to earth)

To Earth Radial velocity Doppler shift only measures the radial velocity (i.e. velocity component along the line-of-sight to earth)

To Earth Radial velocity = - V max Doppler shift only measures the radial velocity (i.e. velocity component along the line-of-sight to earth)

Some data

P You can measure the orbital period directly

P The height of the curve tells you the maximum radial velocity 2V max

so

Transit method (light curves)

Transit method (light curves) Light meter

Transit method (light curves) Light meter

Transit method (light curves) Light meter

Transit method (light curves) Light meter

Transit method (light curves) Light meter

Transit method (light curves) Light meter

Transit method (light curves) Light meter

Transit method (light curves) Light meter

Transit method (light curves) Light meter

Transit method (light curves) Light meter

Transit method (light curves) Light meter

677 in 2013 EXO-PLANET DATABASE

Kepler mission ( ) and K2 (2014-) Monitors over 145,000 stars Uses the transit method 4,696 candidates (as of 10/2015) 1,030 confirmed 12 Small habitable zones confirmed 24 confirmed from K2

M = ?

Imaginative picture of the day Kepler-452b: What It Would Be Like to Live On Earth's 'Cousin'

What have we learned from all these planets? They’re out there There’s a far wider variety of planet types than we see in our own solar system! To explain these types, our basic model for solar-system formation will need some tweaking!

Jupiter mass Saturn mass Neptune mass Earth mass Earth orbitMerc’s orbit1/10 AU 10 x Jupiter mass HOT JUPITERS

Planetary migration Hot jupiters form in the usual way Interaction with the nebular disk makes them spiral in Inward migration continues until star ignites and clears the disk (in our system, the clearing began earlier)

Earth mass 10 x Earth mass Planet radius (Earth radii) WATER WORLDS & SUPER EARTHS

WATER WORLDS Low density (like that of water) Perhaps versions of Neptune or Uranus that were interrupted during their formation due to an ‘early’ solar scouring.

SUPER EARTHS Density like that of earth. How can they acquire so much mass from the nebula ??? Our book speculates, but doesn’t say much.

Conclusions Our model for solar system development needs some tweaking to account for all the new planet types we’re finding Most notably – the idea of planetary migration

One wonders Our present methods for exoplanet detection favor larger planets with short periods Are we biased towards detecting the freaks??? Jupiter period 12 y Earth mass