The Search for Exoplanets and Earths Outside our Solar System · The Doppler Effect The light of a moving source is blue/red shifted by Dl/l o = l-l o /l o = v r /c l o = actual wavelength

The Search for Exoplanets and Earths

Outside our Solar System

Dr. Damian J. Christian Cal State University Northridge

[email protected]

I. Quick notes on our Solar System & Planet

Formation

II. Methods for finding exoplanets

III. Transit Detection and SuperWASP (Wide Angle

Search for Planets)

IV. Characterizing Exoplanets

V. Habitable Zone & Search for Earths

VI. Summary

.

The Search for Planets around

Nearby Stars

Part I. Our Solar System &Planet Formation

Two leading theories:

Core Accretion vs Gravitational Instability

…But first review properties of our Solar System

.

Our Solar System

Rocky planets, Gas Giants & Ice Giants plus smaller objects

Planetary Orbits

Earth

Venus Mercury

All planets in

almost circular

(elliptical) orbits

around the sun,

in approx. the

same plane

(ecliptic).

Sense of

revolution:

counter-clockwise

Sense of rotation:

counter-

clockwise (with

exception of

Venus, Uranus,

and Pluto)

Orbits

generally

inclined by no

more than 3.4o

Exceptions:

Mercury (7o)

Pluto (17.2o)

(Distances and times reproduced to scale)

Solar System Facts • Observed:

Planets orbit Sun in the Same Plane

Generally rotation and revolution in same direction (except Venus,

Uranus and Pluto).

Differentiation: higher densities in inner solar system, lower density

planets in outer solar system

Debris (asteroids, comets, Kuiper Belt objects etc).,

Age measurements (Earth, Moon, Meteorites) all about 4.6 Gyr

Terrestrial Jovian

Small Large

High density Low Density

Low mass High Mass

Great moons not common Great & many moons common

Rings common

Formation and Growth of Planetesimals

Planet formation

starts with clumping

together of grains of

solid matter:

Planetesimals

Planetesimals (few

cm to km in size)

collide to form

planets.

Planetesimal growth through

condensation and accretion.

Gravitational instabilities may have helped in the growth of

planetesimals into protoplanets.

The Story of Planet Building

Planets formed from the same protostellar material

as the sun, still found in the Sun’s atmosphere.

Rocky planet material formed from clumping

together of dust grains in the protostellar cloud.

Mass of less than ~ 15

Earth masses:

Planets can not grow by

gravitational collapse

Mass of more than ~ 15

Earth masses:

Planets can grow by

gravitationally attracting

material from the

protostellar cloud

Earthlike planets Jovian planets (gas giants)

Define a Planet

Planets are defined to be less then 13 Jupiter Masses (MJ)

Above 80 Jupiter Masses an object can fuse

Hydrogen into Helium and become a star

(recall this is 8% the mass of the Sun!)

Objects below 80 MJ are called Brown Dwarfs

M < 13 MJ Planet

13 < M < 80 MJ Brown Dwarfs

M > 80 MJ Small Star

Part II. Methods for finding

Exoplanets

.

Pulsar Timing: Pulsars' signals are extremely regular (spinning neutron star)

Small anomalies in the timing of pulsars can betray the Planets with

masses on order of the Earth's or greater can be detected.

First earth-mass extra-solar planets were confirmed in 1992

Astrometry – wobble on the sky

Gravitational Lensing – enhance starlight

Direct Imaging

Radial Velocities

Photometric Transits

II . Methods for Finding Extra Solar Planets

Pulsar Timing: Pulsars' signals are extremely regular (spinning neutron star)






Direct Imaging

Radial Velocities


Pulsar Timing: Pulsars' signals are extremely regular






Direct Imaging

Radial Velocities


Methods for Finding Extra Solar Planets







Direct Imaging

Radial Velocities


General Relativity

New description of gravity as

curvature of space-time!

This bending of light by the gravitation of massive

bodies has indeed been observed:

During total solar

eclipses:

The positions of

stars apparently

close to the sun

are shifted away

from the position

of the sun.

Now add a planet:







Direct Imaging

Radial Velocities









Direct Imaging

Radial Velocities


Contrast between the Planets and the Sun

Direct Imaging

~109 ~106


Direct Imaging Examples

HR 8799 est 7 -10 Jupiter Masses

b - dist == 68 AU; P = 470 yrs

c - dist = 38 AU; P = 189 yrs

d - dist = 24 AU; P = 100 yrs







Direct Imaging

Radial Velocities



The Doppler Effect

The light of a

moving source is

blue/red shifted by

Dl/lo = l-lo/lo = vr/c

lo = actual

wavelength

emitted by the

source

Dl = Wavelength

change due to

Doppler effect

vr = radial

velocity

vr

Sound waves always travel at the

speed of sound – just like light

always travels at the speed of light,

independent of the speed of the

source of sound or light.

= c/l

Red Shift - longer wavelength

(lower frequencies)

Blue Shift - shorter wavelength

(higher frequencies)

Radial Velocities

Doppler Effect

We do NOT see the planet, only

the shift in the Star’s absorption

lines -- the amplitude of these

depends on the Planets MASS!

=> MpVp = M* V*

QuickTime™ and aSorenson Video 3 decompressorare needed to see this picture.

Radial Velocities

Doppler Effect







Direct Imaging

Radial Velocities



Photometric Transit Detection

QuickTime™ and aYUV420 codec decompressor

are needed to see this picture.

~1%

~ 2 - 3 hrs

First Transits of Extra-Solar Planets

First transit detected by Charbonneau et al (1999): HD209458b

P=3 days and distance 0.04 AU

“Hot-Jupiters”

Current ESP

• 861 planets around 677 stars

• About 20% of ESP are Hot-Jupiters

– (1/20th Earth-Sun distance, P< 4 days!)

• 128 multiple systems

• Only a few Solar System Analogs

Stop: Define Types of Stars

• O

• B

• A

• F

• G

• K

• M

Some Quick Facts:

* A - stars H lines the strongest

* Sun is a G star

* O Stars: H all ionized - no lines!

* B/A stars not enough absorption

lines to do Doppler Method!

Part III. More Details on the Transit Detection

and SuperWASP (Wide Angle Search for

Planets)

.

Photometric Transit Detection

(Why?) Primary Questions:

• What are their sizes and masses?

• What are Hot-Jupiters made of?

• How often do Hot-Jupiters form?

• How do they form?

• Are there habitable planets?

• Earth-sized planets detectable from space

– COROT and NASA’s Kepler

• Ground based astronomy only sensitive to Hot-Jupiters/Saturns

Technique: Need to Monitor 1000’s of stars!

Wide Field Observations of Comets

• Upgrade of detector to

2048x2048 SITe2 chip

• FOV 10x10 degrees, little

vignetting

• Comet Hyakutake 1996B2

• EEV1280x2220 thick detector read out within observatory infra-structure

• Usable FOV 30x40 degrees!

• Nightmare!

Don Pollacco - SuperWASP PI -

lets look for transiting planets by

Monitoring 1000’s of stars….

WASP0: Technology Demonstrator

• Wide Angle Search for Planets prototype camera, total cost about £15K – produced >1GB/night

• Everything commercially available, e.g. detector Apogee 2048x2048 14-bit.

• Operated for 3 months in La Palma and 6 months+ in Greece (2000)

Funded between Queen’s University Belfast / STFC

SuperWASP I La Palma

Use COTS - keep cost down

Enclosure w/ sliding roof

Weather station, GPS system, air-conditioning

Telescope control PC (Linux)

1 PC per camera

Data Storage (2 TB RAID/DLT)

8 camera set-up:

Telescope mount:

Rapid slewing (10o/sec)

Pointing to ~few arcsec

SuperWASP II South Africa

../../SuperWASP/May06/DSCN0885.MOV

Ultra-Wide Field: Sample Image

Surprisingly, wide field

astronomy is relatively new!

4 Camera Image of

Orion (M42)

(1 sec exposure).

15o

D. Christian (QUB)

SuperWASP 8 x 61deg2

WHT Wide-Field Survey: 0.09 deg2

4 deg2

Ultra-Wide Field: Sample Image

5 Camera Image of

Galactic Center

15o - - - - 30 full moons - - - -

ESP Survey fields

• Observations started 16th April 2004

• Overlapping fields at Dec=+28

– Avoid crowding of Galactic Plane

• 30sec exposure time+20 sec overhead

• 8 fields per scan ~8 minute cadence

• Image ~3000 sq. deg each night (~7% of sky)

• Imaged more than 50 million stars to date

X

X

X

Images to light curves

• Factors leading to detection

• Orbital inclination – ~10% should transit

• Depth of transit ~ (Rp/R*)2

• Deeper transits for later-type stars

• Early estimates: 1 to 10 planets per 25,000 stars

Sample ESP Light Curves

Folded light curve (P ~ 11 d)

Light curve First Planet; WASP-1

But wait: Nature is Tricky:

Many other stars can look like a

planet transit: False Positives

Grazing Eclipsing binaries

Foreground binary diluted by faint

background star

Secondary is really a brown dwarf!

False Positives


Foreground Binary diluted by faint

background star

Secondary is really brown dwarf

Background star

False Positives


Foreground Binary diluted by faint

background star


Eliminating False Positives


Foreground Binary diluted by

faint background star


-moderate resolution spectroscopy

-Deeper Imaging ~1m telescope

-Weigh System with Radial Velocities

Planet Confirmation

Weigh System with Radial Velocities

Measure Radial Velocities to ~ few m/s

Star towards us -- blue-shifted

Star away from us -- red shifted

Note: really measure Mpsini

Planet Confirmation: Transit profiles and

Radial Velocity orbits WASP-1 &

WASP-2 first planets discovered 2006!

• Collier Cameron et al 2007

SuperWASP Planets: WASP 1 to 15 !!!

There are >90 SuperWASP planets now (60+ published!)

Part IV. Characterizing Exoplanets

.

Spectra during primary

eclipse: Chemical composition,

scattering properties

Characterize an exoplanet‘s atmosphere: Transmission

Spectroscopy

The Planet‘s Atmosphere

Atmosphere

Star

Planet

What’s in their atmospheres? • Atmospheric composition may be similar to cool brown-

dwarf stars with Teff ~ 1000K

– Optical spectra dominated by alkali-metal absorption?

– Silicate cloud decks?

• Silhouette of planet during transit should appear larger in

strong absorption lines of alkali metals:

Opaque silicate cloud deck

Extended atmosphere

With gaseous Na, K, H2O, CH4, ...

Line photons blocked

high in atmosphere

Continuum photons

blocked by clouds

Extended Lyman a silhouette

• Vidal-Madjar et al (2003) Nature 422, 123

Are Hot-Jupiters disappearing!?

• Heating of the star on the Hot-Jupiter’s atmosphere

may cause it to evaporate.

Deadly Tides Mean Early Exit for Hot Jupiters http://www.sciencedaily.com/releases/2010/09/100912064227.htm

Spitzer IR imaging - secondary eclipse

Planet behind star - depth 7 times smaller!

We can measure the decrease in light when the planet is eclipsed

by the a star and build a temperature profile as a function of

orbital phase

IR Temperature of an Extra Solar Planet

Part V. Habitable Zone &

The Search for Earths

.

• Exoplanet detections limits

• Search for “super-Earths” a few to 10 x ME

Searching for life Searching for life as we know it: The 1st step is to find a rocky planet in the stellar

habitable zone (HZ) - can have liquid water, although it could also be a satellite of a gas giant.

The planet should be in the Galactic habitable zone, not in a globular cluster or close to the Galactic center.

The planet should not be tidally locked, ruling out most late-type stars.

The system should not be young, so that there are not too many catastrophic comet/asteroid impacts.

Find an atmosphere that shows out of equilibrium composition, containing known biomarkers.

Refernce: Dante Minniti (U. Católica)

Terrestrial planets – the Holy grail…

April 2007:

- Discovery of 5ME (minimum mass) planet around M3 dwarf star 20 light years

away: Gliese 581c

- Orbits star in 13 days

- Resides in warm edge of Habitable zone

- Computer models suggest rocky or ocean world

“continuously habitable zone (or CHZ)”

- liquid water for main sequence lifetime

• Press gets very excited about “Habitable”

exoplanets!

New!! Space Satellites to find Earth-sized

transiting planets: CoRot and Kepler

Kepler: launched March 2009:

3.5+ yr mission to find Earth-

like planets

Kepler MISSION

CONCEPT • Kepler Mission is optimized for finding

habitable planets ( 0.5 to 10 M )

in the HZ ( near 1 AU ) of solar-like stars

• Continuously and simultaneously

monitor 100,000 main-sequence stars

• Use a one-meter Schmidt telescope:

FOV >100 deg2 with an array of 42 CCD

• Photometric precision:

Noise < 20 ppm in 6.5 hours V = 12 solar-like star

=> 4s detection for Earth-size transit

• Mission:

Heliocentric orbit for continuous viewing

> 3.5 year duration

58

59

Kepler SPACECRAFT

Schmidt Corrector 0.95 m dia.

Spider with Focal Plane

and Local Detector Electronics

Focal Plane

95 Mega pixels, 42 CCDs

Primary Mirror

1.4 m dia., 85% lt. wt.

Sunshade

Upper Telescope Housing

Lower Telescope Housing

Spacecraft bus integration

Fully assembled Kepler photometer

Mounted on the spacecraft

60

FIELD OF VIEW IN

CYGNUS

The Kepler star field is a part of the extended solar neighborhood in

the Cygnus-Lyra regions along the Orion arm.

It is located on one side of the summer triangle (Deneb-Vega-Altair)

Sample Kepler ESP

• Kepler-11 - new 6 planet system!

• Kepler 10 = Earth-sized planet

• 4.5ME and 1.4 RE

http://kepler.nasa.gov/Mission/discoveries/kepler10b/

New Kepler ESP

• Kepler-22b - planet in HZ size 2.4 REarth

• P ~ 290 days 0.85 AU

Kepler-16 = orbits a binary star

• Kepler 37b - smallest yet (Feb 2013)

Kepler 37 - 215 LY distant

3 planets

13 days - b - 0.30 REarth

21 days - c - 0.74

39.8 days - d - 1.99

• Using Kepler data, researchers estimate

that six percent of red dwarf stars in the

galaxy have Earth-size planets in the

"habitable zone,"

Reference: Dante Minniti (U. Católica)

Searching for life

Infrared

Spectra:

The

Ozone

test

FUTURE MISSIONS

• TESS: Searching Closer to Home

• The Transiting Exoplanet Survey Satellite is being designed to search for the most promising exoplanet targets for next-generation studies.

Summary & The Future… • Over 670 planets systems known - Kepler with quadruple this

• Mostly discovered with indirect methods

• Improved imaging/RV promises smaller ESP detections

• Future space missions for discovery and characterization

• > 90 extra-solar planets from SuperWASP - from transits

» FUTURE:

• New ESP Candidates from 2013+ season

– Require spectroscopic follow-up

– Exciting prospect to measure planet's atmosphere with Hubble/Spitzer Space Telescopes

• Earth-size planets now!! CoRoT & Kepler

– Ton a public Kepler data to analyze!

• Further our understanding on how planets form

• Search for Life in the Galaxy

http://www.superwasp.org

Questions?

http://www.superwasp.org/

Planet Candidates as of June 2010

Orbital Period in days

Siz

e R

ela

tive

to

Ea

rth

Jun

2010

Planet Candidates as of Feb 2011


Siz

e R

ela

tive

to

Ea

rth

Jun

2010

Feb 2011

Planet Candidates as of Dec 2011


Siz

e R

ela

tive

to

Ea

rth

Jun

2010

Feb

2011

Dec

2011

Sizes of Planet Candidates

207

680

1181

203

27 (+204%)

(+136%)

(+78%)

(+23%)

(+42%)

Earth-size −

Super Earth-size −

− Neptune-size

− Jupiter-size

− Super

Jupiter-size

Exoplanet Materials on-line http://kepler.nasa.gov/education/EducationandPublicOutreachProjects/

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

http://www.scientificamerican.com/article.cfm?id=7-amazing-exoplanets-interactive

http://hubblesite.org/ & http://www.stsci.edu

EXTRASOLAR PLANETS ESO October 2005 Dante Minniti (U. Católica)

The Moon as seen from the Earth. The Earth as seen from the Moon

(only18% land).

Woolf et al. (2002), Arnold et al. (2002)

Eathshine + scattered moonlight before substraction

Earthshine spectrum

A Census of the Stars (2)

Faint, red dwarfs

(low mass) are

the most

common stars.

Giants and

supergiants

are extremely

rare.

Bright, hot, blue

main-sequence

stars (high-

mass) are very

rare.

Masses of Stars in the Hertzsprung-

Russell Diagram = Star’s Lifetime

The higher a star’s mass,

the brighter it is:

High-mass stars have

much shorter lives than

low-mass stars:

Sun: ~ 10 billion yr.

15 Msun: ~ 11 million yr.

0.1 Msun: ~ 3 trillion yr.

L ~ M3.5

tlife ~ M-2.5

40 Msun: ~ 1 million yr!!!

Only way to get masses of stars:

Weigh them in binaries!!

Documents

The Search for Exoplanets and Earths Outside our Solar System · The Doppler Effect The light of a moving source is blue/red shifted by Dl/l o = l-l o /l o = v r /c l o = actual wavelength