Imaging and characterization of extrasolar planets

Bruce MacintoshJames Graham

Steve Strom

Travis Barman, Lisa Poyneer, Mitchell Troy, Mike Liu, Stan Metchev

2

Outline

• Science motivation and expected landscape in 2015• Four key science missions

– Robust statistical sample of giant extrasolar planets– Characterization of extrasolar planet atmospheres and abundances– Studies of circumstellar debris disks– Detection of young planets and protoplanetary disks

• Comparisons: 8 vs 30 vs 50 m• Brief discussion of space missions• Excessive generalizations and conclusions

• Missing: Mid-IR spectroscopy and imaging, Doppler, transit characterization…

3

Known Doppler planets

4

Predicting Exoplanet Research in 2016

Key question: how do solar systems form?

• What are the physical conditions in planet forming disks?– What are the heating & cooling processes in disks?– What is the origin of viscosity?– How do condensates grow & what is the particle size spectrum vs. time?– What is the nature of disk-planet interactions?

• What are the relative roles of global gravitational instability & core accretion?

– Can core-accretion form super-Jupiters?– Can Jovian planets form in inner disks (< 5 AU)?– What is the relation between Jovian & terrestrial planet formation?

• Early disk-planet evolution?– What is the accretion rate onto a protoplanet?– What role do density waves and gaps play in controlling planet growth?– What controls dissipation & dispersal of disks?– How and when does migration occur?

• What can the properties of exoplanets tell us about their formation history?

• With GSMT, these questions can be studied through studying planet populations as a function of age

5

Direct detection in the next decade

• Conventional AO– Detect hot very young (<20 Myr) planets in wide

(>50 AU) orbits• Extreme AO on 8-m telescopes (Gemini,

VLT + others): 2010– Direct detection of warm self-luminous planets

(selects for (<1 Gyr) and massive)– Probes outer parts of target systems– Low-res (40-100) spectroscopic characterization

• Interferometry – 5-micron emission (LBT)– Differential phase / astrometry (VLT, Keck)– Small number of target systems

• Space: – TPF no earlier than 2020– Possible 2-m-class Jovian planet imagers

20-sec. Gemini Planet Imager 5 MJ/200 Myr planet @ 0.6

arcseconds

VLT/NACO 5 MJ / 8 MYr

6

Cooling extrasolar planets

Current AO 0.5-2”

8-m Extreme AO 0.2-1”

30-m Extreme AO 0.06-1”

7

Monte Carlo planet population: GPI

8

Detected planets for I<8 mag Gemini Planet Imager field survey

Gemini Planet Imager field survey completeness contours

9

10

Four key science missions and requirements

1. Detect and characterize a large sample of extrasolar planets (Teff, R, g)• Overlap with Doppler is

desirable

2. High-SNR spectroscopy of planets (abundances)

3. Detection of planets in the process of formation and shortly after (1-30 Myr)

4. Studies of circumstellar dust on AU scales

10-8 @ 50 mas, I<8 magR~100 spectroscopyHundreds of planets and

thousands of targets

R~1000 spectroscopy

10-6 @ 30 mas, H<10 IR WFS, Polarimetry

Polarimetry 2”+ FOV

11

Modeling and assumptions

• Three simulation levels• “Full AO” simulations

– No assumptions other than Taylor frozen-flow/multilayer atmospheres

– AO, DM control loop dynamics– Primary mirror effects– Exposure times <5 seconds– Code limited to 30-m case– Various coronagraphs possible

• Monte Carlo simulations– “Generic” AO system– Statistical assumptions about atmosphere

speckle lifetimes derived from Full AO sims– Exposure time up to several minutes– Used for 30, 50, 99-m case– Nonphysical ideal apodizer coronagraph

• Analytic error budgets– Used to evaluate long-exposure static effects

• Contrast varies strongly with star brightness, instrument architecture, etc.

12

ExAO contrast noise sources

Inner working angle2-5 /D

Speckle contrast1/(D2 t1/2)

Photon contrast1/(D2 t1/2 )

Systematic/static contrastWeak D, t dependence

13

Comparison between 30 and 50 m

1 AU

5 AU

0.1 AU G5 star @ 10 pc

14

Equivalent to a factor of 8 exposure time + factor of 2 better control of static errors

15

Overlap with Doppler searches

3/D (30m)3/D (50m)

16

Planetary Spectroscopy

• Composition is destiny– The zero-temperature

equilibrium radius is determined by the chemical composition

• Composition is a primary window on the formation of the planets in the solar system

– Order of magnitude range in abundances from planet to planet, e.g., C ranges from x3 (Jupiter) – x30 (Uranus/ Neptune)

– Jovian abundances rule out formation by gravitational collapse

Zapolsky & S

alpeter 1965

17

Spectral characterization: R=100 for Teff and gravity/mass

• Differential exoplanet spectra indicate that R ≈ 100 is suitable for measuring atmospheric parameters

– [1.5] - [1.6] is a good effective temperature indicator

– [1.5] – [2.2] is a good gravity indicator

– Higher spectral resolution may address composition of hot Jupiters

Spectra are calculated using fully self-consistent models with the PHOENIX atmosphere code

18

Spectral characterization: R=100 for Teff and gravity/mass

• Differential exoplanet spectra indicate that R ≈ 100 is suitable for measuring atmospheric parameters

– [1.5] - [1.6] is a good effective temperature indicator

– [1.5] – [2.2] is a good gravity indicator

– Higher spectral resolution may address composition of hot Jupiters

Spectra are calculated using fully self-consistent models with the PHOENIX atmosphere code

19

Planets discovered by a ExAO field survey: 30 vs 8 m

T dwarfs

Jupiter

Mas

s

Age

30-m

8-m

20

Spectral characterization: R=1000 for composition

• High spectral resolution shows individual molecular features at R=1000

• Features are much stronger in cool planets

• This opens up the possibility of directly probing (atmospheric) composition

800 K

800 K

500 K

400 K

300 K

21

Spectroscopic sensitivity

G5 star @ 10 pc

22

Planet formation

• A survey of young stars will show when & where planets form– Detection of young Jovian planets in situ is evidence for core accretion– Planets in circular orbits in young systems (~ 10 Myr) at large semimajor axis

separation must have formed by gravitational instability– Co-existence of planets & disks will illuminate disk-planet interactions

• Planet formation & survival in multiple star systems and stellar clusters– Does disk disruption in binaries prevent planet formation?– When is photoevaporation of disks important?– Tidal stripping in dense clusters?

• Requires very small inner working distance• Complex systems with planets and disks - polarimetry?

T Tauri star, 150 pc with 3 MJ companion in optically thick disk

23

Accretion history of planets determines luminosity later in life

• In different formation scenarios, planets will have complex luminosity histories

1. Runaway dust accretion then exhaustion of solid material

2. Slow gas accretion3. Runaway gas accretion

until growth is shut off by opening of gap in disk or dissipation of nebula

• Each phase will have a distinct radiative signature

• Initial conditions influence future evolution

Hubickyj et al. 2005, Icarus, in press

24

Accretion history of planets determines luminosity later in life

• In different formation scenarios, planets will have complex luminosity histories

1. Runaway dust accretion then exhaustion of solid material

2. Slow gas accretion3. Runaway gas accretion

until growth is shut off by opening of gap in disk or dissipation of nebula

• Each phase will have a distinct radiative signature

• Initial conditions influence future evolution

Fortney et al. 2005, PPV

1

2

3

25

Key parameter is Inner Working Angle => /D

26

Comparison: 30 vs 50 m for young systems

• 3 /D on an obscured aperture requires advanced/complicated coronagraphs

– Shearing nulling interferometer (low throughput)

– Pupil remapping (unproven)– Phase / diffraction cancellation

(half field of view, chromatic)• 5 /D can be achieved with

conventional coronagraphs

• Very challenging for <30m• Reduced technological risk

on 50-m• Alternatively, 50-m can study

these scales at longer wavelengths

Stop

Starlight frompre- AO

Mach-ZenderNuller (DSS)

DeformableMirror

Modulator

DM Controller

WFS Camera

Processor

Science IFU

SpatialFilter

TMT shearing interferometer + 2 hour

sensitivity map

27

Circumstellar dust disks

• Dust disks in other solar systems are an important part of planetary systems

• Structure in dust can trace planets that are too low-mass to be detected

• GSMT may be able to access Zodiacal dust analogs

– Current debris disks are Kuiper belts

• More modeling is needed but also very challenging 100 Myr solar system model

(Metchev, Wolf) with ~10-3.5 at 130 pc from Keck NGAO

study

• Debris disks are primarily diffuse structures– Sensitivity does not necessarily improve with angular resolution– Sensitivity is limited by systematic errors / PSF subtraction artifacts– High Strehl well-known PSF is more important than aperture

AU Mic debris diskUH 2.2m: R-band (0.6 um)

100 AUKalas, Liu & Matthews (2004)

Keck 10-m AO: H-band (1.6 um)0.04” FWHM = 0.4 AU

Liu(2004)

29

TPF JPF

30

Conclusions

• This area is extremely speculative: we don’t yet know the limits of ExAO on 8-m

• Detection of Jovian planet population– Telescope aperture determines survey time and survey size– Larger telescopes have greater overlap with Doppler surveys

• Characterization of Jovian planets– R=100 spectroscopy can determine macroscopic properties– R=1000 can determine abundances but is photon-starved

• In situ observations of planet formation– Unique capability of extremely large ground-based telescopes– Requires inner working angles ~0.03 arcseconds at moderate

contrast– For a 30-m, requires an advanced (unproven) coronagraph– For a 50-m, more straightforward

• Debris disk science– Important; needs modeling; independent of aperture