EXAM II COMING UP Monday Oct 19th

(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 MJ

68 AU

~7 MJ

24 AU

Recall Jupiter’s orbit is 5.2 AU

170 light-years

~4 MJ

41 AU

DISTANCE: ~500 light-years

~ 35(?) MJ

~ 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

MS MP

a

Circular orbit example

center of mass

MS MP

aPS

P

MM

Ma

32

2

)(

4a

MMGP

PS

PS

S

MM

Ma

If we can “see” the star’s wobblei.e. measure P and RS

Then we can infer a and MP

PS

PS MM

MaR

32

2

)(

4a

MMGP

PS

Astrometric method – measure the star’s wobble directly

The claim: Jupiter-sized planetDiscredited !

only 6 ly away

GAIA

up and running – no exoplanet results yet(primary mission is parallax measurements)

Slightly bluer light

Slightly redder light

cV0

v

V

Ha

Doppler shift method(radial velocity method)

S R

max V

To Earth

Radial velocity 0

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

S R

max V

To Earth

Radial velocity

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

S R

max V

To Earth

Radial velocity = Vmax

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

S R

max V

To Earth

Radial velocity = 0

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

S R

max V

To Earth

Radial velocity

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

S R

max V

To Earth

Radial velocity = -Vmax

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

2Vmax

S R

max V

PVRπ S max 2cirm.

2 max PV

RS

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

EXO-PLANET DATABASE

Kepler mission (2009-13) 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

Eart

h or

bit

Mer

c’s o

rbit

1/10

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

Plan

et ra

dius

(Ear

th ra

dii)

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 Eart

h m

ass