exam ii coming up monday oct 19 th (a week from this coming monday!) hw5 due a week from today
TRANSCRIPT
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