Using New Techniques in the Search Using New Techniques in the Search for Extrasolar Planetary Systems: for Extrasolar Planetary Systems:

Are we unique?Are we unique?

Phil HinzUniversity of Arizona

Associate Professor

Director, Center for Astronomical Adaptive Optics

Jupiter at 5 μm wavelengthTaken with MIRAC at the 6.5 m MMT

Outline:•What we know about other planets•Technology to directly image them.•What we might find out.

What we know about other What we know about other planetary systemsplanetary systems

The Solar System (Simplified)The Solar System (Simplified)

Radius: 1 0.01 0.1Mass: 1 0.000005 0.001Distance: 1 5Ang. Separationat 10 pc 0.1” 0.5”

How do we detect extrasolar planetsHow do we detect extrasolar planets(What’s wrong with this picture?)(What’s wrong with this picture?)

Indirect detection techniquesIndirect detection techniques

•Doppler shift of the starlight•Light from the star will have a periodic motion to the Doppler shift of its spectrum (about 1 m/s for Jupiter). The ~500 planets detected have used this technique.

•Movement of star’s position on the skyA star with a planet orbiting it will appear to wobble back and forth by a small amount (1 milliarsecond if it is identical to Jupiter). This technique has not yet been successful.

•Transit of the planet in front of the sunIf the orbital plane is aligned with our line of sight we will see the starlight appear to dim once per orbit. Two planets have been detected with this technique.

Properties of Other Planetary Systems

•planets appear to be like Jupiter

• more massive planets than in

our system

•planets are close to their stars

•Less massive planets are more

common

Properties of extrasolar planets• many more highly eccentric orbits than in our Solar

System

•Planets are typically found around stars with a higher

fraction of heavy elements (higher metallicity in

astronomy jargon).

Planets discovered by Doppler shiftPlanets discovered by Doppler shift

The likelihood of detecting a planet appears to be dependent on how metal-rich it is.

A Transiting PlanetA Transiting Planet The Doppler technique yields only planet masses and orbits. Planet must eclipse or transit the star in order to measure its radius. Size of the planet is estimated from the amount of starlight it blocks.

• We must view along the plane of the planet’s orbit for a transit to occur.

– transits are relatively rare• They allow us to calculate

the density of the planet.– extrasolar planets we have

detected have Jovian-like densities.

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Measuring the Size of a Planet

When a planet passes in front of a star it blocks out a portion of its light.

The amount of light it blocks depends on how big the planet is.

Change in Intensity = Rplanet2 / Rstar

2

Transits we have seen, have decreased the star's flux by about 1%.

So, How common are planetary systems?

We can only see the most massive (Jupiter-like) planets in other systems,

and only out to about 4 Astronomical Units, yet we have found many

planetary systems.

The fraction of stars with planets could be quite high!

Roughly 10 out of every 100 stars have been detected to have planets

The actual fraction may be higher!

Planets might be in longer orbits.

Planets might have a low enough mass that they are undetectable currently.

Could any of these planets harbor life?

A star called Gl 581 has 6(!) low mass planets, b, c , d, e,f,g.

Gl 581 c is >5 Earth masses (ME) and at 0.07 AU

Gl 581 d is >7 ME and at 0.25 AU

Gl 581 g is >3 (ME) at 0.15 AU

Could these be habitable? Artist's Conception!(not actual

image)

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Goldilock’s planet

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What might we learn in the next decade?

Doppler velocity detections will find increasing numbers of planets that are

less massive and in larger orbits.

If other planetary systems are like our own, the massive planets are typically

at larger separations.

These take a long time to detect with Doppler velocity, but we may be able to

see them directly.

Large telescopes are needed to see the very faint planets.

We need to have telescopes which can form sharp images and get rid of the

glare from the star.

New Technology for Direct New Technology for Direct Imaging of PlanetsImaging of Planets

Why do we want to directly “see” planets?

l Light obtained directly from a planet could tell us quite a bit additional

information about it.

- Size

- Temperature

- Existence and composition of an atmosphere.

l Planets far from their parent star take a long time to complete an

orbit.

- Indirect methods such as Doppler velocity detection becomes difficult.

MMT and LBT

The 6.5 m MMT telescope is currently

being used to search for planets just

south of Tucson.

The Large Binocular Telescope (2x8.4 m)

is being completed and will begin searching

for planets soon!

Telescopes on the ground will likely

not be able to detect planets as small

as Earth.

What type of planets might we see directly?

From the ground:

Telescopes on the ground are

beginning by looking for Jovian

planets.

Larger (brighter)

More massive (bigger effect on

star)

Using a telescope in space:

Space missions will extend the search

to look for Terrestrial planets.

Fainter (smaller)

Less massive (smaller effect on star)

Concepts for NASA's

Terrestrial Planet Finder Mission

The Large Binocular Telescope

on Mt. Graham, AZ

The physics behind planet emission

The light peaks at a particular

wavelength which depends on an

object's temperature.

T (deg. Kelvin) = 2900 / λ (microns)

Any object at a temperature

above absolute zero (0 K= -273

C) emits light.

If we plot the amount of light

versus wavelength it has a

characteristics shape called a

blackbody curve

The advantage of looking for planets in the Infrared

l Planets in the habitable zone will mainly radiate infrared radiation.

Wavelength

Brightness

The difficulty of detection: Brightness differences

l Earth, seen from a distance, is ten

billion times fainter than the Sun.

- In the infrared it is only ten million

times fainter.

l Jupiter in the infrared is a million

times fainter than the Sun.

l Earth around a nearby star will be

0.1 arcsec away (this is about the

resolution limit of HST)

Trying to see a Planet around another

star is like trying to detect a firefly

circling a distant spotlight

Contrast DemonstrationContrast Demonstration

Motivation for Direct DetectionMotivation for Direct DetectionPlanets Verification, mass determination

– For known radial velocity planets we could verify existence and determine the mass

Look for long-period planets– Separations >5 AU require a long period of observations for detection (>10

years)

Learn about size, temperature, and composition of planets– Most information about a planet can be obtained from direct detection.

Zodiacal Dust Disks Disks are the “smoking gun” of a planetary system

– Material is cleared away on short timescales requiring large planetessimal bodies as reservoirs for transitory dust around mature stars.

Dust may prevent terrestrial planet detection– A dust disk brighter than the solar system’s would add background and force

longer integration times. If the dust is irregular it may mimic a planet signal.

Extrasolar Giant Planet SpectraExtrasolar Giant Planet Spectra

IR spectra by Adam Burrows and team predicting the flux of knownplanets around 55 Cnc

Nulling Interferometry: Concept

Cause starlight to interfere destructively in order to suppress the “glare” of the star.

Constructive DestructiveDetector

Telescope 1 Telescope 2

Light from star Light from star

First Telescope Demonstration of First Telescope Demonstration of NullingNulling

Nulling at the MMTNature 1998; 395, 251.

Ambient Temperature Optics

The Bracewell Infrared The Bracewell Infrared Nulling Cryostat (BLINC)Nulling Cryostat (BLINC)

BLINC has been in routine use for mid-IR observations with the MMT and Magellan since June 2000.

•Primary targets have been young, luminous (A-type) stars with significant IR excess.

•We are also starting to look at older (main sequence) stars for evidence of zodiacal dust emission.

BLINC at the MMT and BLINC at the MMT and Magellan TelescopesMagellan Telescopes

from N. Smith et al., 2002

HD 100546: A young Solar System?HD 100546: A young Solar System? Constructive Null

ε Mus

HD 100546

•Disk approximately 25 AU in diameter. •disk shape is consistent with Near-Infrared scattered light images.•Disk similar in size at 11 microns and 24.5 microns.•Consistent with an inner hole? (Bouwman et al.)

10.3 microns (~silicates)11.7 microns (~PAH)12.5 microns (continuum)

position angle

null

MMT Adaptive OpticsMMT Adaptive Optics Adaptive optics (AO) are needed to allow high-

precision suppression of the starlight. Deformable secondary system integrates the AO

system into the telescope, keeping the reflections to a minimum for good IR sensitivity.

Deformable secondary mirror of theMMT during engineering tests in June2002 (courtesy Francois Wildi).

IC 2149 at 2.1 microns. (courtesy Patrick A. Young, Donald W. McCarthy, and the ARIES-MMTAO team.)

The MMT AO System

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[7736-12]

Astronomical Telescopes and Instrumentation 2010, June 27-July2, San Diego, 2010

Paper 7736-12

Intensities between open and closed loop rescaled for displaying purposes.

LBT InfraRed Test Camera images: H band, 10mas/pixel scale

The object:HD 124085, K0, R=7.5 , I=6.9, H=5.8, Triple StarThe atmosphere:seeing 0.6arcsec V band Elevation 58..64FLAO parameters:1 KHz, 30x30 subaps, 400 corrected modesResults: SR H 65%..73%

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3.2 arcsec

From the MMT to the LBTFrom the MMT to the LBTThe MMT provides a testbed for developing nulling interferometry in preparation for the LBT. It will provide sensitive nulling observation of the very nearest stars

The Large Binocular Telescope will have both better sensitivity and resolution for exo-system searches

MMT

LBT

6.5 m

8.4 m22.8 m

Why combine the light?

LBT Deformable Secondary Mirror

LBTI installed on the telescope

LBTI uses both mirrors to create a 23 m telescope

The AO system increases the resolution by 20x.

Combining the telescopes increase the resolution by

another 3x

The Large Binocular TelescopeThe Large Binocular Telescope

The Large Binocular Telescope is currently being constructed on Mt. Graham in Arizona. It is a collaboration of Arizona, Germany, Italy, Ohio State University, and the Research Corporation.When completed it will be the world’s largest single-mount telescope.

LBT Structure in 2002LBT Structure in 2002

The telescope enclosure is complete on Mt. Graham in Arizona

LBT enclosure on Mt. Graham

LBT Structure ConstructionLBT Structure Construction

The structure is being assembled inside the enclosure

LBT under ConstructionLBT under Construction

The LBT Interferometer (LBTI)The LBT Interferometer (LBTI)

The Main Components of LBTIThe Main Components of LBTI

UBC= Universal Beam CombinerNIL= Nulling Interferometer for the LBTNOMIC= Nulling Optimized Mid-Infrared Camera

UBC=Universal Beam CombinerNIL=Nulling Interferometer for the LBTNOMIC=Nulling-Optimized Mid-Infrared Camera

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Larg

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nocu

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eles

cope

In

terf

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(UA)

The beginning of high resolution science

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What might we find out?What might we find out?

Earth: A pale blue dot• Voyager 1 mapped the outer

planets in the 1970-80s. On its

way out of the solar system in

1990 it turned around an image

of our Earth.

• At this point it was 27 AU

(0.0004 light years) from the

Earth.

• The Earth appears as a single

blue pixel in the image.

Other planets imaged by Voyager 1

• Even at this distance the

planets are almost

indistinguishable.

• Jupiter appears to be slightly

bigger than the Earth (it is

really 10 times bigger) but by

how much is difficult to tell.

A more recent view from the Cassini mission

• Even from 10 AU the Earth is

essentially a point of light,

bluish in color.

• We can barely see the Moon in

a blow-up of the image.

• A planet around a nearby star

is nearly a million times further

away.

• It will be even fainter.

• The angle between a planet

and its parent star will be very

small.

How can we learn more about other planets?Planets will appear as

points of light

We will not be able

to see things like clouds

or continents

We will see their brightness

vary for different wavelengths.

What could we see once we “null” the star?

5 micron image 15 micron image 25 micron image

We may soon be able to see planets around other stars as single points of light.

The information about these planets will come from their brightness at each wavelength.

Simulated Images of what we might see

Spectrum of 4 planets in the infrared

Deriving Planetary Information: Size

• The planets are unresolved points of light.

• The bigger they are the more light they will emit.

• If one planet is twice the size of another it would appear four times as

bright.

Which planet is the largest?

Deriving Temperature

The light peaks at a particular

wavelength which depends on

an object's temperature.

Hotter objects have a peak

brightness that is at shorter

wavelength

You might say it is “bluer”

Which planet is the hottest?

Deriving Atmospheric

Composition

• The gases in an atmosphere

will absorb the infrared light

being emitted by the planet's

surface.

• Absorption lines tell us what is

in the atmosphere around a

planet.

• The amount of transmission is

less for a more abundant gas.

• Levels in the drawing are marked

relative to the amount in Earth's

atmosphere.0.33

1.0

3.0

10.0

0.33

1.0

3.0

10.0

CO2

CH4

H2O

O3

Which planet has ozone?

How can we learn more about other planets?

CO2 -> planet

has atmosphere

H2O -> planet is

habitable

O3-> planet

has life!

We will see their brightness

vary for different wavelengths.

Recap: Spectra of Planets

• We can derive several parameters from the spectra of

these planets:

• Size of the planet

• Mass

• Temperature

• can compare to distance from star.

• Albedo

• Greenhouse effect?

• Atmosphere Constituents

• Surface conditions

• Habitability

• Life

Points to Take Away:

Other planetary systems exist! They appear to be relatively common (~10%

of stars have them).

We are just beginning to develop the capability to “see” other planetary

systems.

Earth-like planets are much more difficult to detect, but are the ultimate goal

of most of this research.

Jupiter-like planets are being pursued as a good signpost of other systems.

The systems we have found so far indicate we may have more diversity in

other systems than we expected.

Are we unique?

Interesting WebsitesInteresting Websites

LBT: http://www.lbto.org

LBTI: http://lbti.as.arizona.edu

MMT: http://www.mmto.org

NASA:http://planetquest.jpl.nasa.gov

BACK UP SLIDESBACK UP SLIDES

Original Bracewell nulling Original Bracewell nulling interferometer conceptinterferometer concept

Target: Jupiter in solar system twin at 10 pc, 0.5 arcsec

Method; two element interferometer in space, set for destructive interference for star, constructive for planet. Spin about line of sight to modulate planet signal

Wavelength: 40 um

req’d element separation 7 m (planet on 1st constructive peak)

planet / star @ 40 mm 1/5000

sin2 leak 1/400,000

planet / nulled star 80

Bracewell proposed space infrared nulling interferometer to detect thermal emission of giant exo-planets (Nature, 1978)

Planet ModulationPlanet Modulation from Bracewell and McPhie, Icarus, 1979 from Bracewell and McPhie, Icarus, 1979

1. The pitch of the sin2 fringes is chosen so the first constructive peak is at the expected planet location. The leak due to the finite star disc is then minimized

2. The interferometer is rotated at frequency w during an observation so the planet is alternately transmitted and blocked, appearing as a signal at 2w.