Extrasolar Planets

1
Extrasolar Planets
Our solar system includes all that orbits our
sun 9 planets, asteroids, comets,
meteoroids, dust, gas. In 1995 we found the
first planet orbiting another star the
first extrasolar planet, or exoplanet.
2
How we Find Extrasolar Planets
Indirect Methods 1) Doppler shift of the stars
orbit nearly all detections so
far 2) Astrometric wobble of the stars
orbit no planets found so far Semi-direct
Methods 1) Transits (light blocked by the
planet) a few 2) Microlensing (planets
gravity) none so far Direct Methods none so
far next major step 1) Planet imaged directly
(perhaps with coronograph) reflected or emitted
(IR or radio) light 2) Planet imaged by
interferometer
3
Astrometry changing position of star in sky
Best for large orbits (which take a long time),
nearby stars. Interferometry will allow very
small motions to be measured.
4
Changing Doppler (Radial) Velocity
Shift is 1 part in 100 million
5
Discovery of Extrasolar planets
Information from a graph of Doppler velocity
against time period, semimajor axis,
eccentricity, lower limit on the mass of the
planet (Mass lt some value)
6
Hot Close in Jupiters A Big Surprise
Discovered some stars with Jupiter mass planets
very near the stars hot Jupiters.
15 of known exoplanets, but a smaller fraction
of all planets, since hot Jupiters have short
periods and large velocities that are easiest to
find. The first discovery, 51 Peg, had a 4 day
orbit (0.05 AU!) and the mass of Jupiter.
7
Properties of the systems found
Another surprise was that many of the orbits are
eccentric (like binary stars). In a few cases,
there are several planets.
8
How did the close Jupiters get there?

• They could have been dragged there by the
  accretion disk.
• Corollary some planets fall into the star!
• They could have gotten there by interacting with
  another planet.
• They could have formed there (direct collapse
  mechanism?)

9
Transits
Dimming of the star if the planet crosses in
front. Amount from ratio of their areas 1 for
Jupiter and 0.008 for the Earth. Seen for one
planet, confirming earlier radial velocity
detection.
HST measurement of HD209458
10
NASAs Kepler Project
Transits will tell us the fraction of stars with
terrestrial mass planets (none known now).
A wide-view telescope monitors 100,000 stars in a
single field for gt4 years to detect Earth-size
planets

• May Find hundred terrestrial planets within 2 AU
  of stars
• For Earth-size and larger planets, determines
• Frequency
• Size distribution
• Orbital distribution
• Association with stellar characteristics

Sunshade
Launched 2007?
11
Microlensing Gravity of the planet as a lens
A second way to find Earth-mass planets. Measure
brightness of 107 stars with 1 accuracy every
hour for years.
The downside is that you will only detect the
planet once, as its star passes in front of a
background star.
12
Why Direct Imaging is Hard
The star is much brighter than its star. gt109 in
optical, 106 in infrared Young planets are
hotter, emit more infrared. The planet is close
in angle (lt arcsec) to the star. Need coronograph
and AO with extreme performance to remove light
from star that would hide planet.
109
Reflected light
Thermal emission
No coronograph
coronograph
13
Discovered 110 Exoplanets
The list of discoveries is http//www.ciw.edu/bos
s/IAU/div3/wgesp/planets.shtml Radial Velocity
Discoveries 108 Transit Discoveries
5 Microlensing Discoveries 1 Planets around a
pulsar 3 around one pulsar, 1 around a
second Other methods - Astrometry, Direct
Imaging -- all zero We have never seen the light
from an exoplanet. Radial Velocity Detections
are typically more massive than Jupiter. Only 3
are the mass of Neptune. 55 Cancri has 4 known
planets.
14
eXtreme Adaptive Optics Planet Imager XAOPI

• Goal Direct imaging of a scientifically
  significant sample of extrasolar planets
• First AO system optimized for high contrast and
  to sweep out a dark hole region
• Other science circumstellar debris disks,
  evolved stars, solar system targets
• CfAO study for a dedicated planet-detection AO
  system for an 8-10m telescope. Began in November
  2003
• PI Bruce Macintosh.
• Project Scientist James Graham
• Institutions LLNL, UCB, UCSC, JPL, STScI (UCLA)

Simulation of XAOPI image 4 M_Jupiter, 500 Myr
old planet 6 AU from star at 10 pc. Star makes
all the rest of the light here that is suppressed.
15
XAOPI (or Gemini ExAOC) can detect a significant
population of planets

• Every dot represents a planet
• Circled dots are discovered by radial-velocity
  survey
• Squares will be discovered by ExAO
• XAOPI will find 7 of planets around brighter
  stars near to sun.
• Detection rate gt50 for young-stars because young
  planets emit more infrared.
• ?H20 means planet is 108 times fainter that star
  in near Infrared

Angle from star to planet, 1.22diffraction limit
16

• pfound_keck_ecl_radv_xao.png

Exoplanets in 2010 circles are expected XAOPI
discoveries
17
Goals of Direct Imaging
First spectra of exoplanets molecules in
atmosphere water, ammonia.. atmosphere
pressure and temperature age of planet Number
of planets different distances from young stars
tell how planetary systems formed Looking for
10M to begin construction
18
Space Interferometric Missions
For 1B in coming decades will directly image
older exoplanets, including terrestrials
Darwin
Terrestrial Planet Finder
19
Eventually, imaging terrestrial planets?
Oxygen or Ozone in spectrum suggests plant life,
as on Earth