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Extrasolar Planets
Some prehistory
• Absence of evidence clearly was not
evidence of absence – planets dim and
situated next to brilliant stars
• Laplace and Kant ideas had vastly different
implications
• (Don’t fixate yet on possible habitats!)
History
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1952: Struve proposes radial-velocity search
1963-9: van de Kamp, Barnard’s Star astrometry
1990- HST FGS astrometry
1994 Wolszczan – first pulsar planets!
1995 Queloz/Meyor 51 Peg hot Jupiter
1995- Marcy/Butler/Fisher team
Now 155 planets from radial velocities
“Neptunes” and smaller
Otto Struve, The Observatory, Oct 1952:
40 years of devilish details
• Mechanical stability of spectrographs – need
measurement series of parts per billion
accuracy spanning years
• Software to unravel subtle atmospheric and
instrumental effects
• Who knew there would be planets a hundred
times easier to find than Jupiter?
155 worlds and counting
More heavy elements – more planets
What we know and don’t
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Metal-rich stars have more planets
Many orbits are very eccentric
Multiplanet systems exist
Some binary/triple stars keep close planets
Just now getting to Neptune-mass planets
Terrestrial extrasolar planets still only inferred
More techniques
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Transit photometry
Dynamics of dusty rings (“exo-Kuiper belts”)
Gravitational lensing
Interferometry – imaging and astrometry
Coronagraphy
Transit detections
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Edge-on orbits
Favors large and close-orbiting planets
Can survey large numbers of stars at once
Statistics if not targeted stars’ systems
Followup of Doppler planets – sizes, rings,
evaporating atmospheres, temperatures
Transit variations
Doppler shift
Brightness
Sizes of giant planets
(ESO)
Hubble and the evaporating
atmosphere of HD 209458b
Vidal-Madjar
et al. 2004
We see H,C,O,Na… on the way out (it’s hot)
Spitzer and planet temperatures
TrES-1, Charbonneau et al. AstrophysJ 2005
Do this at multiple wavelengths and
get a crude planetary spectrum
HD 209458, Deming et al. Nature 2004
Places we don’t see transits
More transits
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STARE/Sleuth/Sherlock
OGLE, other microelensing surveys
MOST? (CSA)
Kepler (NASA)
COROT (CNES)
Eddington (ESA)
Planets decenter and warp rings
b Pictoris
a PsA = Fomalhaut
Gravitational lensing
• General relativity: a distant mass can
concentrate light
• Star-star microlensing is seen if we watch
enough stars (millions)
• Planets at the right place have a distinct
signature, now seen
• Existing data precise enough to have shown
terrestrial-mass planets
Star-star microlensing
Now add a planet:
Lensing planet around OGLE-2005-BLG-71
Udalski et al.,
OGLE+MOA teams,
June 2005. Note need
for rapid response!
Enter Interferometry
• Classic problems: stellar glare, atmospheric blur
• Even HST doesn’t quite (yet?) separate planets’
reflected light from stars
• Combining separated telescopes can help, both in
resolution and by nulling out most of the starlight.
• Optical-wavelength interferometry is technically
challenging. For real.
Interferometers
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CHARA, COAST, NPOI (mostly stellar)
Palomar testbed
Keck
ESO VLT
Into space – SIM, TPF-I, Darwin
What Goldin had in mind “that would be
tears”
Palomar Testbed Interferometer
Terrestrial Planet Finder (TPF)
aka Planetquest
Just like the
name says
One element or
many? Yes…
ESA’s Darwin breaks the chains
Interferometer of
free-flying 3m
telescopes (2015?)
Identify and
characterize
nearby terrestrial
worlds.
TPF-I
• Look in IR, where contrast is best
• Need some spectral resolution anyway ; same
detectors would see atmospheric absorption
from free oxygen (O2 and O3), CO2
• Amount of exo-zodiacal dust is crucial
• May need to be at Jupiter’s distance, plus
cryogenically cool 4x1.5m telescopes
Looking far ahead: TPI
• Terrestrial Planet Imager
• Multiple free-flying telescopes, precisely
controlled for beam combination
• Example: five four-telescope
interferometers (8m each), hundreds of km
apart
• Goal: many resolution elements across disk
of planets found by TPF
Amateurs get into the game!
• t Bootis planet detected spectroscopically
with 16” telescope and fiber-optic
spectrograph (Tom Kaye et al.,
www.spectrashift.com)
• Key lensing observations of star/planet
system by two New Zealand amateurs
(Grant Christie, Jennie McCormick) with
10-14” telescopes
Even multiple-star systems
• 55 Cancri, 16 Cygni, g Cephei (hints from 1992
data!) have planets, are in wide binaries
(compared to planet orbits, anyway)
• Simulations: planets within 3 AU of a Centauri
components would still be stable
• Formation?!?
Multiple-planet systems
How many
ways can giant
planets form?
SuperJovians or brown dwarfs?
ESO VLT
HST
History of planetary systems
• Dynamics, TNOs imply early evolution of
orbits in solar system
• Disk interactions predicted hot Jupiters!
• Resonances imply ongoing interaction in
other systems
• Not particularly aligned with Milky Way
• Pulsar planets may be “reborn” systems
Implications for exobiology
bioastronomy astrobiology
life-bearing planets
• Many sunlike stars have giant planets; the
more metal-rich the better
• Many of these are in places hostile to
terrestrial planets
• Moons may offer rich pickings, opening up
faint, cool stars for habitable zones
• Interstellar probes can start with significant
knowledge of the target systems
p.s. we still apparently don’t
know all the solar planets…