esp

Document Sample
esp Powered By Docstoc
					The Search for
Extra-Solar
Planets

Dr Martin Hendry
Dept of Physics and Astronomy                          P1Y*
                                                     Frontiers
                                                    of Physics
http://www.astro.gla.ac.uk/users/martin/teaching/
                                                     Feb 2007
Extra-Solar Planets

 One of the most active and
 exciting areas of astrophysics
 Well over 200 exoplanets discovered
  since 1995
Extra-Solar Planets

 One of the most active and
 exciting areas of astrophysics
 Well over 200 exoplanets discovered
  since 1995

Some important questions

  o How common are planets?
  o How did planets form?
  o Can we find Earth-like planets?
  o Do they harbour life?
Extra-Solar Planets

 One of the most active and
 exciting areas of astrophysics
 Well over 200 exoplanets discovered
  since 1995


What we are going to cover

 How can we detect extra-solar planets?
 What can we learn about them?
1. How can we detect extra-solar planets?

 Planets don’t shine by themselves; they just
  reflect light from their parent star

     Exoplanets are very faint
1. How can we detect extra-solar planets?

 Planets don’t shine by themselves; they just
  reflect light from their parent star

     Exoplanets are very faint

 We measure the intrinsic brightness of a
  planet or star by its luminosity


         Luminosity,    L   (watts)
Luminosity varies with
                          Betelgeuse
wavelength (see later)

e.g. consider Rigel and
Betelgeuse in Orion




                           Rigel
Luminosity varies with
                          Betelgeuse
wavelength (see later)

e.g. consider Rigel and
Betelgeuse in Orion

Adding up (integrating)
L at all wavelengths
 Bolometric luminosity
 e.g. for the Sun

   Lbol  4 10 W 26

                           Rigel
Stars radiate isotropically
(equally in all directions)

     at distance r, luminosity spread over
      surface area 4 r 2




 (this gives rise to the Inverse-Square Law )
Planet, of radius R, at distance r from
star
                             R
                                              2
                                     R
                                  2
Intercepts a fraction    f          
of LS                        4 r 2
                                      2r 
Planet, of radius R, at distance r from
star
                              R
                                               2
                                      R
                                   2
Intercepts a fraction     f          
of LS                         4 r 2
                                       2r 

Assume planet reflects all of this light

                              2
                  LP  R 
                    
                  LS  2r 
Examples

Sun – Earth:
   R  6.4  10 6 m     LP            10
                           4.6  10
   r  1.5 1011 m      LS
Examples

Sun – Earth:
   R  6.4  10 6 m     LP            10
                           4.6  10
    r  1.5 1011 m     LS

Sun – Jupiter:
   R  7.2  10 m7
                           LP          9
                              2.110
   r  7.8  10 m11
                           LS
2nd problem:
Angular separation of star and exoplanet is tiny

Distance units

Astronomical Unit = mean Earth-Sun distance


            1 A.U.  1.496 10 m   11
2nd problem:
Angular separation of star and exoplanet is tiny

Distance units

Astronomical Unit = mean Earth-Sun distance


            1 A.U.  1.496 10 m   11



   For interstellar distances: Light year

         1 light year  9.461 10 m     15
                                           r
e.g. ‘Jupiter’ at 30 l.y.        Star          Planet


  d  30 l.y.  2.8 10 m   17


  r  5 A.U.  7.5 10 m    11


                                  d
                 r
     tan    
                 d

   2.7 10 radians
               6

               4
                                                
     1.5  10 deg                 Earth
e.g. ‘Jupiter’ at 30 l.y.

  d  30 l.y.  2.8 10 m   17


  r  5 A.U.  7.5 10 m    11




                 r
     tan    
                 d

   2.7 10 radians
               6

               4
     1.5  10 deg
Exoplanets are ‘drowned out’ by their parent
star. Impossible to image directly with current
telescopes (~10m mirrors)

      Keck telescopes
      on Mauna Kea,
      Hawaii
Exoplanets are ‘drowned out’ by their parent
star. Impossible to image directly with current
telescopes (~10m mirrors)

Need OWL telescope:
100m mirror,
planned for next
decade?
                                   100m



                             ‘Jupiter’ at 30 l.y.
1. How can we detect extra-solar planets?

 They cause their parent star to ‘wobble’, as
  they orbit their common centre of gravity
1. How can we detect extra-solar planets?

 They cause their parent star to ‘wobble’, as
  they orbit their common centre of gravity




       Johannes Kepler           Isaac Newton
Kepler’s Laws of Planetary Motion
1) Planets orbit the Sun in an
   ellipse with the Sun at one
   focus
Kepler’s Laws of Planetary Motion
1) Planets orbit the Sun in an
   ellipse with the Sun at one
   focus
2) During a planet’s orbit
   around the Sun, equal areas
   are swept out in equal times
Kepler’s Laws of Planetary Motion
1) Planets orbit the Sun in an
   ellipse with the Sun at one
   focus
2) During a planet’s orbit
   around the Sun, equal areas
   are swept out in equal times
Kepler’s Laws of Planetary Motion
1) Planets orbit the Sun in an
   ellipse with the Sun at one
   focus
2) During a planet’s orbit
   around the Sun, equal areas
   are swept out in equal times
3) The square of a planet’s
   orbital period is
   proportional to the cube of
   its mean distance from the
   Sun
                       Kepler’s Laws, published 1609, 1619
                                          Newton’s gravitational
                                          force provided a physical
                                          explanation for Kepler’s
                                          laws

                                                   G m1 m2
                                              FG      2
                                                     r


Newton’s law of Universal Gravitation,
Published in the Principia: 1684 - 1686
Star + planet in circular
orbit about centre of
mass,  to line of sight
Star + planet in circular
orbit about centre of
mass,  to line of sight
Star + planet in circular
orbit about centre of
mass,  to line of sight

Can see star ‘wobble’,
even when planet is
unseen.

But how large is the
wobble?…
Star + planet in circular   Centre of mass condition
orbit about centre of            m1r1  m2 r2
mass,  to line of sight
                                              mS 
                                              m 
                            r  rS  rP  rS 1    
Can see star ‘wobble’,
                                                 P 
even when planet is
unseen.

But how large is the
wobble?…
Star + planet in circular       Centre of mass condition
orbit about centre of                m1r1  m2 r2
mass,  to line of sight
                                                  mS 
                                                  m 
                                r  rS  rP  rS 1    
Can see star ‘wobble’,
                                                     P 
even when planet is
unseen.                     e.g. ‘Jupiter’ at 30 l.y.

But how large is the          mS  2.0 1030 kg
wobble?…                      mP  1.9 1027 kg
                                   rS
                               S  radians
                                   d
                                  1.5  10 7 deg
                                  Detectable routinely with
                                     SIM Planet Quest
                                    (launch date 2010?)
                                     but not currently
                               See www.planetquest.jpl.nasa.gov/SIM/



The Sun’s “wobble”, mainly due to Jupiter, seen from 30
light years away    = width of a 5p piece in Baghdad!
Suppose line of sight is in
orbital plane




                          Direction
                          to Earth
Suppose line of sight is in
orbital plane

Star has a periodic motion
towards and away from
Earth – radial velocity
varies sinusoidally




                          Direction
                          to Earth
Suppose line of sight is in   Detectable via the
orbital plane                 Doppler Effect
Star has a periodic motion
towards and away from
Earth – radial velocity
varies sinusoidally




 Can detect motion from shifts in spectral lines
Spectral lines arise when
electrons change energy
level inside atoms.

This occurs when atoms
absorb or emit light
energy.

Since electron energies
are quantised , spectral
lines occur at precisely
defined wavelengths


                             hc
                  E  h 
    Planck’s constant
                             
      Absorption
     Electron absorbs
     photon of the precise
     energy required to
     jump to higher level.
e-   Light of this energy
     (wavelength) is         e-
     missing from the
     continuous spectrum
     from a cool gas
        Emission
     Electron jumps down
     to lower energy level,
     and emits photon of
     energy equal to the
     difference between
     the energy levels.
                              e-
     Light of this energy
e-   (wavelength) appears
     in the spectrum from
     a hot gas
                                                  Hydrogen Spectral Line Series
                         15                                                                       Brackett
                                       Ionised above 13.6 eV                                  m = 5,6,7,…      n=4

                                                                                                                  n=4
                                                                                                                  n=3
                                                                            Paschen
Energy difference (eV)




                                                                        m = 4,5,6,…   n=3
                                                                                                                  n=2
                         10                           Balmer
                                                  m = 3,4,5,…    n=2



                                                                Shown here are downward transitions, from higher
                                                                to lower energy levels, which produce emission
                         5                                      lines. The corresponding upward transition of the
                                                                same difference in energy would produce an
                                                                absorption line with the same wavelength.




                                                                                                                n=1
                                    Lyman                                                                   (ground state)
                              m = 2,3,4,…   n=1
     Star


Laboratory
How large is the Doppler motion?

Equating gravitational and circular accleration

For the planet:-                      Angular velocity

   FC  mP  rP 2G mP mS                         2
                     r 2                       
                                                  T
For the star:-                               Period of ‘wobble’
                  G mP mS
   FC  mS  rS 2

                     r2
How large is the Doppler motion?

Equating gravitational and circular accleration

For the planet:-                      Angular velocity

   FC  mP  rP 2G mP mS                         2
                     r 2                       
                                                  T
For the star:-                               Period of ‘wobble’
                  G mP mS
   FC  mS  rS 2

                     r2
How large is the Doppler motion?

Equating gravitational and circular accleration

For the planet:-                      Angular velocity

   FC  mP  rP 2G mP mS                         2
                     r 2                       
                                                  T
For the star:-                               Period of ‘wobble’
                  G mP mS
   FC  mS  rS 2

                     r2
Adding:-
                          GmS  mP 
            rP  rS  
             2
                               2
                             r
         4 2 r 3
 2r 3      2
                   G mS  mP   Gm S
          T
         4 2 r 3                             Kepler’s
 2r 3      2
                   G mS  mP   Gm S      Third Law
          T

The square of a planet’s orbital period is proportional
    to the cube of its mean distance from the Sun
         4 2 r 3                                   Kepler’s
 2r 3      2
                   G mS  mP   Gm S            Third Law
          T

The square of a planet’s orbital period is proportional
    to the cube of its mean distance from the Sun

e.g.   Earth:
  r  1 A.U.      T  1 year

       Jupiter:
                      3        3

                                   
                   rE    rJ
  r  5.2 A.U.        2
                         2            TJ  5.23  11.86 years
                   TE    TJ
Amplitude of star’s radial velocity:-
                          (mS  mP ) rS
       v S   rS      r                 From centre of
                              mP          mass condition
Amplitude of star’s radial velocity:-
                          (mS  mP ) rS
       v S   rS      r                         From centre of
                              mP                  mass condition



                           (mS  mP ) rS
                            2             3   3

         GmS  mP                 3
                                 mP
Amplitude of star’s radial velocity:-
                            (mS  mP ) rS
       v S   rS        r                               From centre of
                                mP                        mass condition



                             (mS  mP ) rS
                             2                3   3

         GmS  mP                     3
                                     mP

                       (mS  mP ) v S T
                                 2   3                2   3

         G mP
                 3
                                       
                                          mS v S T
                             2             2
Amplitude of star’s radial velocity:-
                            (mS  mP ) rS
       v S   rS        r                                  From centre of
                                mP                           mass condition



                             (mS  mP ) rS
                             2                   3   3

         GmS  mP                        3
                                        mP

                       (mS  mP ) v S T
                                    2   3                2   3

         G mP
                 3
                                       
                                          mS v S T
                             2             2

                    2 G 
                             1/ 3

             vS         mS
                               2 / 3
                                      mP
                    T 
       2 G                              G  6.673 10 11 m 3 kg -1s -2
                1/ 3
                  2 / 3
 vS         mS        mP
       T                                 mSun  2.0  10 30 kg


Examples

     Jupiter:      mJup  1.9 1027 kg            T  11.86 years
                       v S  12 .4 ms -1
       2 G                              G  6.673 10 11 m 3 kg -1s -2
                1/ 3
                  2 / 3
 vS         mS        mP
       T                                 mSun  2.0  10 30 kg


Examples

     Jupiter:      mJup  1.9 1027 kg            T  11.86 years
                       v S  12 .4 ms -1

     Earth:
                   mEarth  6.0  10 24 kg        T  1 year

                   v S  0.09 ms -1

           Are these Doppler shifts measurable?…
Stellar spectra are
observed using prisms
or diffraction gratings,
which disperse starlight
into its constituent
colours
 Stellar spectra are
 observed using prisms
 or diffraction gratings,
 which disperse starlight
 into its constituent
 colours

          Doppler formula
Change in                                Radial
wavelength                               velocity


                    v
                    
                  0 c
 Wavelength of light as       Speed
 measured in the laboratory   of light
 Stellar spectra are
 observed using prisms
 or diffraction gratings,
 which disperse starlight
 into its constituent
 colours

          Doppler formula
Change in                                Radial
wavelength                               velocity


                    v                             Limits of current technology:
                    
                  0 c                                 
                                                              300 millionth
                                                        0
 Wavelength of light as       Speed

                                                                v  1 ms -1
 measured in the laboratory   of light
The Search for
Extra-Solar
Planets

Dr Martin Hendry
Dept of Physics and Astronomy                          P1Y*
                                                     Frontiers
                                                    of Physics
http://www.astro.gla.ac.uk/users/martin/teaching/
                                                     Feb 2007
51 Peg – the first new planet
                           Discovered in 1995

                           Doppler amplitude

                                v  55 ms   -1
51 Peg – the first new planet
                           Discovered in 1995

                           Doppler amplitude

                                   v  55 ms           -1



                           How do we deduce planet’s
                           data from this curve?



                                  2 G 
                                              1/ 3
                                             2 / 3
                            vS         mS        mP
                                  T 

                            We can observe     We can infer this
                             these directly     from spectrum
Stars are good approximations
       to black body radiators

Wien’s Law
The hotter the temperature, the
shorter the wavelength at which
the black body curve peaks


           Stars of different colours
           have different surface
           temperatures


             We can determine a star’s
                 temperature from its
                            spectrum
                                         Surface temperature (K)                                       When we plot the
                            25000   10000    8000 6000     5000 4000 3000
                                                                                                       temperature and
                                                                                                       luminosity of stars
                     106                                                    -10



                                                       Supergiants                                     on a diagram most
                     104                                                    -5
                                                                                                       are found on the
                                                                                                       Main Sequence
                     102                                  Giants            0
Luminosity (Sun=1)




                                                                                  Absolute Magnitude
                      1                                                     +5




                10-2                                                        +10




                10-4                                                        +15




                           O5 B0    A0      F0    G0      K0   M0    M8

                                          Spectral Type
                                                   Surface temperature (K)                                                      When we plot the
                                25000         10000       8000 6000
                                                             .
                                                                            5000 4000 3000
                                                                                                                                temperature and
                                                                      . .
                                                                                                                                luminosity of stars
                     106                                                                             -10
                                                  Deneb              .
                           .. .
                             Rigel      . .
                            . ..               ..                . ..
                                                                       Betelgeuse
                                                                                                                                on a diagram most
                                                                                                                                are found on the
                                                                        Antares
                     104
                              ..                          .
                                                                                                     -5

                                 .
                               ...                            .. ....
                                                                 Arcturus                                                       Main Sequence
                           Regulus .. .          . .. ...... ... .
                                                                                        Aldebaran


                     102         Vega
                                      ... .. . ........ .                                            0
Luminosity (Sun=1)




                                Sirius A                                                 Mira




                                                                                                           Absolute Magnitude
                                         . .. .                                     Pollux
                                                                                                                                Stars on the
                                               .. ... .            Procyon A


                      1
                                                  . .. .
                                              Altair                         Sun
                                                                                                     +5                         Main Sequence
                                                        . ....
                                                          . .
                                                               ....                                                             turn hydrogen
                10-2
                                                                . ...
                                                                    ..                                                          into helium.
                               . ..                                 ..                               +10

                               . ....                                ....
                                         .. ..                         ..        Barnard’s
                                                                                                                                Stars like the
                           Sirius B                                    ..        Star

                10-4                             . .                                                                            Sun can do this
                                                              . .. .
                                                                                                     +15

                                                                        ...
                                           Procyon B

                                                                          .
                                                                           .                                                    for about ten
                              O5 B0          A0         F0       G0         K0       M0         M8                              billion years
                                                       Spectral Type
Main sequence stars obey
an approximate mass–
                                        5
luminosity relation
                                                      3.5
                                                L~m
                                        4
   We can, in turn,
    estimate the mass                   3
    of a star from our




                                  Sun
                                  L
    estimate of its



                           log10 L
    luminosity                          2

                                        1

                                        0

                                    -1
                                            0       0.5       1.0
                                                        m
                                                 log10 m
                                                        Sun
        Summary: Doppler ‘Wobble’ method

                          Stellar
                         spectrum


                          Stellar
                        temperature



                         Luminosity



  Velocity of
stellar ‘wobble’   +      Stellar
                           mass         +     Orbital period


                                            From Kepler’s
                                            Third Law
                       Orbital radius
                        Planet mass
 Complications
 Elliptical orbits
       Complicates maths a bit, but
       otherwise straightforward
       radius      semi-major axis

 Orbital plane inclined to line of sight
       We measure only       v S sin i obs
       If i is unknown, then we obtain a
       lower limit to mP
       ( v S  v S sin i obs as sin i  1 )

 Multiple planet systems
       Again, complicated, but exciting
       opportunity (e.g. Upsilon Andromedae)

   Stellar pulsations
       Can confuse signal from planetary ‘wobble’
In recent years a growing number of exoplanets have been detected via
transits = temporary drop in brightness of parent star as the planet
crosses the star’s disk along our line of sight.




             Transit of Mercury: May 7th 2003
             Change in brightness from a planetary transit

Brightness
                                             Star

               Planet




                                                             Time
Ignoring light from planet, and assuming star is uniformly bright:

   Total brightness during transit
                                           
                                                   
                                               B*  R  R
                                                        2
                                                        *
                                                             2
                                                             P            RP 
                                                                      1  
                                                                                   2


  Total brightness outside transit                B*  R*2                R 
                                                                           S


e.g.     Sun:        RSun  7.0  10 8 m
         Jupiter:    RJup  7.2 107 m                Brightness change of ~1%

         Earth:     REarth  6.4  10 6 m             Brightness change of ~0.008%
Ignoring light from planet, and assuming star is uniformly bright:

   Total brightness during transit
                                           
                                                   
                                               B*  R  R
                                                        2
                                                        *
                                                             2
                                                             P            RP 
                                                                      1  
                                                                                   2


  Total brightness outside transit                B*  R*2                R 
                                                                           S


e.g.     Sun:        RSun  7.0  10 8 m
         Jupiter:    RJup  7.2 107 m                Brightness change of ~1%

         Earth:     REarth  6.4  10 6 m             Brightness change of ~0.008%


 If we know the period of the planet’s orbit, we can use the width of
 brightness dip to relate RP , via Kepler’s laws, to the mass of the star.

 So, if we observe both a transit and a Doppler wobble for the same
 planet, we can constrain the mass and radius of both the planet and its
 parent star.
Another method for finding planets is gravitational lensing

The physics behind this method is based on Einstein’s General Theory of
Relativity, which predicts that gravity bends light, because gravity causes
spacetime to be curved.
                                              This was one of the first
                                              experiments to test GR:
                                              Arthur Eddington’s 1919
                                              observations of a total
                                              solar eclipse.
 Another method for finding planets is gravitational lensing

 The physics behind this method is based on Einstein’s General Theory of
 Relativity, which predicts that gravity bends light, because gravity causes
 spacetime to be curved.
                                                                      This was one of the first
                                                                      experiments to test GR:
                                                                      Arthur Eddington’s 1919
                                                                      observations of a total
                                                                      solar eclipse.




                                                                     GR passed
                                                                      the test!


“He was one of the finest people I have ever known…but he
didn’t really understand physics because, during the eclipse of
1919 he stayed up all night to see if it would confirm the bending
of light by the gravitational field. If he had really understood
general relativity he would have gone to bed the way I did”
                                         Einstein, on Max Planck
Another method for finding planets is gravitational lensing

If some massive object passes between us and a background light source, it can
bend and focus the light from the source, producing multiple, distorted images.
Another method for finding planets is gravitational lensing

If some massive object passes between us and a background light source, it can
bend and focus the light from the source, producing multiple, distorted images.
Another method for finding planets is gravitational lensing

If some massive object passes between us and a background light source, it can
bend and focus the light from the source, producing multiple, distorted images.
Another method for finding planets is gravitational lensing

If some massive object passes between us and a background light source, it can
bend and focus the light from the source, producing multiple, distorted images.




    Multiple images of the same background quasar, lensed by a foreground spiral galaxy
Even if the multiple images are too close together to be resolved separately,
they will still make the background source appear (temporarily) brighter.
                               Background stars

Lens’ gravity focuses the
light of the background star
on the Earth




                                   Gravitational lens

                               So the background star
                               briefly appears brighter
Even if the multiple images are too close together to be resolved separately,
they will still make the background source appear (temporarily) brighter.

We call this case gravitational microlensing. We can plot a light curve showing
how the brightness of the background source changes with time.




                             The shape of the
                             curve tells about
                             the mass and
                             position of the
                             object which
                             does the lensing




                                                 Time
Even if the multiple images are too close together to be resolved separately,
they will still make the background source appear (temporarily) brighter.

We call this case gravitational microlensing. We can plot a light curve showing
how the brightness of the background source changes with time.

If the lensing star
has a planet which also
passes exactly between
us and the background
source, then the light
curve will show a second
peak.

Even low mass planets can
produce a high peak (but for
a short time, and we only
observe it once…)

Could in principle detect Earth mass planets!
What have we learned about exoplanets?
   Highly active, and rapidly changing, field




     Aug 2000: 29 exoplanets
What have we learned about exoplanets?
   Highly active, and rapidly changing, field




     Aug 2000: 29 exoplanets




                                   Sep 2005: 156 exoplanets
What have we learned about exoplanets?
    Highly active, and rapidly changing, field




       Aug 2000: 29 exoplanets

 Up-to-date summary at
 http://www.exoplanets.org


 Now finding planets at larger
 orbital semimajor axis             Sep 2005: 156 exoplanets
What have we learned about exoplanets?
Why larger semi-major axes now?
                                        2 G 
                                               1/ 3
                                                   2 / 3
 Kepler’s third law implies      vS         mS        mP
  longer period, so requires            T 
  monitoring for many years to
  determine ‘wobble’ precisely
What have we learned about exoplanets?
Why larger semi-major axes now?
                                          2 G 
                                                 1/ 3
                                                     2 / 3
 Kepler’s third law implies        vS         mS        mP
  longer period, so requires              T 
  monitoring for many years to
  determine ‘wobble’ precisely

 Amplitude of wobble smaller (at
  fixed mP ); benefit of improved
  spectroscopic precision
What have we learned about exoplanets?
Why larger semi-major axes now?
                                           2 G 
                                                   1/ 3
                                                      2 / 3
 Kepler’s third law implies         vS         mS        mP
  longer period, so requires               T 
  monitoring for many years to
  determine ‘wobble’ precisely

 Amplitude of wobble smaller (at
  fixed mP ); benefit of improved
  spectroscopic precision

Improving precision also now
finding lower mass planets
(and getting quite close to
Earth mass planets)
      For example:                                5.9 mEarth
                                             mP 
      Third planet of GJ876 system                  sin i
What have we learned about exoplanets?
Discovery of many ‘Hot Jupiters’:
Massive planets with orbits closer to
their star than Mercury is to the Sun
Very likely to be gas giants, but with
surface temperatures of several
thousand degrees.




                                         Mercury
What have we learned about exoplanets?
Discovery of many ‘Hot Jupiters’:
Massive planets with orbits closer to
their star than Mercury is to the Sun
Very likely to be gas giants, but with
surface temperatures of several
thousand degrees.




                                                             Mercury




                                         ‘Hot Jupiters’ produce Doppler
                                         wobbles of very large amplitude
    Artist’s impression of ‘Hot
    Jupiter’ orbiting HD195019           e.g. Tau Boo:   v S sin i  474 ms -1
Existence of Hot Jupiters is a
challenge for theories of star
and planet formation:-

Star forms from gravitational
collapse of gas cloud. Angular
momentum conservation 
proto-planetary disk


Orion Nebula
Existence of Hot Jupiters is a
challenge for theories of star
and planet formation:-

Star forms from gravitational
collapse of gas cloud. Angular
momentum conservation 
proto-planetary disk


Orion Nebula
Existence of Hot Jupiters is a
challenge for theories of star
and planet formation:-

Star forms from gravitational
collapse of gas cloud. Angular
momentum conservation 
proto-planetary disk


Orion Nebula
Forming stars
and planets….

     versus


   The nebula spins
   more rapidly as it
   collapses
Forming stars
and planets….             versus

As the nebula collapses
a disk forms
Forming stars
and planets….            versus

Lumps in the disk form
planets
What have we learned about exoplanets?

  Computer modelling indicates that a Hot Jupiter could not form
   so close to its star and maintain a stable orbit

  Current theory is that Hot Jupiters formed further out in the
   protoplanetary disk, and ‘migrated’ inwards due to tidal
   interactions with the disk material during its early evolution.
What have we learned about exoplanets?

  Computer modelling indicates that a Hot Jupiter could not form
   so close to its star and maintain a stable orbit

  Current theory is that Hot Jupiters formed further out in the
   protoplanetary disk, and ‘migrated’ inwards due to tidal
   interactions with the disk material during its early evolution.

 How common are ‘Hot Jupiters’?
  We need to observe more planetary systems before we can
   answer this. Their common initial detection was partly because
   they give such a large Doppler wobble.
    As sensitivity increases, and lower mass planets are found, the
    statistics on planetary systems will improve.
Looking to the Future

 1.   The Doppler wobble technique will not be sensitive enough to
      detect Earth-type planets (i.e. Earth mass at 1 A.U.), but will
      continue to detect more massive planets
Looking to the Future

 1.   The Doppler wobble technique will not be sensitive enough to
      detect Earth-type planets (i.e. Earth mass at 1 A.U.), but will
      continue to detect more massive planets
 2.   The ‘position wobble’ (astrometry) technique will detect
      Earth-type planets – Space Interferometry Mission after 2010
       (done with HST in Dec 2002 for a 2 x Jupiter-mass planet)
Looking to the Future

 1.   The Doppler wobble technique will not be sensitive enough to
      detect Earth-type planets (i.e. Earth mass at 1 A.U.), but will
      continue to detect more massive planets
 2.   The ‘position wobble’ (astrometry) technique will detect
      Earth-type planets – Space Interferometry Mission after 2010
       (done with HST in Dec 2002 for a 2 x Jupiter-mass planet)

 3.   The Kepler mission (launch
      2008?) will detect transits
      of Earth-type planets, by
      observing the brightness
      dip of stars
Looking to the Future

 1.   The Doppler wobble technique will not be sensitive enough to
      detect Earth-type planets (i.e. Earth mass at 1 A.U.), but will
      continue to detect more massive planets
 2.   The ‘position wobble’ (astrometry) technique will detect
      Earth-type planets – Space Interferometry Mission after 2010
       (done with HST in Dec 2002 for a 2 x Jupiter-mass planet)

 3.   The Kepler mission (launch
      2008?) will detect transits
      of Earth-type planets, by
      observing the brightness
      dip of stars

      (already done in 2000 with
       Keck, and now becoming routine
       for Jupiter mass planets, e.g.
       from OGLE and SuperWASP)
Transit Detection by OGLE III program in 2003
www.superwasp.org
Transit detections by SuperWASP from 2006
Transit detections by SuperWASP from 2006
Looking to the Future

 1.   The Doppler wobble technique will not be sensitive enough to
      detect Earth-type planets (i.e. Earth mass at 1 A.U.), but will
      continue to detect more massive planets
 2.   The ‘position wobble’ (astrometry) technique will detect
      Earth-type planets – Space Interferometry Mission after 2010
       (done with HST in Dec 2002 for a 2 x Jupiter-mass planet)

 3.   The Kepler mission (launch
      2008?) will detect transits
      of Earth-type planets, by               Note that (2) and (3)
      observing the brightness                permit measurement of
      dip of stars                            the orbital inclination

      (already done in 2000 with
                                                  Can determine mP
       Keck, and now becoming routine              and not just mP sin i
       for Jupiter mass planets, e.g.
       from OGLE and SuperWASP)
Saturn mass planet in transit across HD149026
From Doppler wobble method   From transit method
                                                   From Sato et al 2006
Looking to the Future

 4.   Gravitational microlensing satellite?              Launch date ????
      Could detect mars-mass planets




                                       Jan 2006: ground-based detection of a 5 Earth-mass
                                                 planet via microlensing
Looking to the Future

 5.   NASA: Terrestrial Planet Finder
       ESA: Darwin                      }    ~ 2015 launch???

      These missions plan to use nulling interferometry to ‘blot out’
      the light of the parent star, revealing Earth-mass planets
Looking to the Future

 5.   NASA: Terrestrial Planet Finder
       ESA: Darwin                      }     ~ 2015 launch???

      These missions plan to use nulling interferometry to ‘blot out’
      the light of the parent star, revealing Earth-mass planets
      Follow-up spectroscopy would search for signatures of life:-

                                       Spectral lines of oxygen, water
                                       carbon dioxide in atmosphere




                                            Simulated ‘Earth’ from 30 light years
The Search for Extra-Solar Planets

o The field is still in its infancy, but there are exciting times ahead
o In about 10 years more than 200 planets already discovered
The Search for Extra-Solar Planets

o The field is still in its infancy, but there are exciting times ahead
o In about 10 years more than 200 planets already discovered
o The Doppler method ultimately will not discover Earth-like
  planets, but other techniques planned for the next 15 years will
o Search methods are solidly based on
  well-understood fundamental physics:-
    Newton’s laws of motion and gravity
    Atomic spectroscopy
    Black body radiation
The Search for Extra-Solar Planets

o The field is still in its infancy, but there are exciting times ahead
o In about 10 years more than 200 planets already discovered
o The Doppler method ultimately will not discover Earth-like
  planets, but other techniques planned for the next 15 years will
o Search methods are solidly based on
  well-understood fundamental physics:-
    Newton’s laws of motion and gravity
    Atomic spectroscopy
    Black body radiation

o By ~2020, there is a real prospect of
  finding not only Earth-like planets,
  but detecting signs of life on them.
The Search for Extra-Solar Planets

o The field is still in its infancy, but there are exciting times ahead
o In about 10 years more than 200 planets already discovered
o The Doppler method ultimately will not discover Earth-like
  planets, but other techniques planned for the next 15 years will
o Search methods are solidly based on
  well-understood fundamental physics:-
    Newton’s laws of motion and gravity
    Atomic spectroscopy
    Black body radiation

o By ~2020, there is a real prospect of
  finding not only Earth-like planets,
  but detecting signs of life on them.

    What (or who) will we find?…

				
DOCUMENT INFO
Shared By:
Categories:
Tags:
Stats:
views:0
posted:11/17/2012
language:English
pages:119