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

• 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

• 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

• Transit photometry

• Dynamics of dusty rings (“exo-Kuiper belts”)

• Gravitational lensing

• Interferometry – imaging and astrometry

• Coronagraphy

Transit detections• 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

We see H,C,O,Na… on the way out (it’s hot)

Vidal-Madjar et al. 2004

Spitzer and planet temperatures

HD 209458, Deming et al. Nature 2004

TrES-1, Charbonneau et al. AstrophysJ 2005

Do this at multiple wavelengths and get a crude planetary spectrum

Places we don’t see transits

More transits

• STARE/Sleuth/Sherlock

• OGLE, other microelensing surveys

• MOST? (CSA)

• Kepler (NASA)

• COROT (CNES)

• Eddington (ESA)

Planets decenter and warp rings Pictoris

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

• 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!

• 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, Cephei (hints from 1992 data!) have planets, are in wide binaries (compared to planet orbits, anyway)

• Simulations: planets within 3 AU of 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…