View
0
Download
0
Category
Preview:
Citation preview
The Search for Exoplanets and Earths
Outside our Solar System
Dr. Damian J. Christian Cal State University Northridge
damian.christian@csun.edu
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)
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
Pulsar Timing: Pulsars' signals are extremely regular
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
Methods for Finding Extra Solar Planets
Pulsar Timing: Pulsars' signals are extremely regular
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
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:
Pulsar Timing: Pulsars' signals are extremely regular
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
Methods for Finding Extra Solar Planets
Pulsar Timing: Pulsars' signals are extremely regular
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
Contrast between the Planets and the Sun
Direct Imaging
~109 ~106
Methods for Finding Extra Solar Planets
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
Pulsar Timing: Pulsars' signals are extremely regular
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
Methods for Finding Extra Solar Planets
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
Pulsar Timing: Pulsars' signals are extremely regular
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
Methods for Finding Extra Solar Planets
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
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
Grazing Eclipsing binaries
Foreground Binary diluted by faint
background star
Secondary is really brown dwarf
Background star
False Positives
Grazing Eclipsing binaries
Foreground Binary diluted by faint
background star
Secondary is really brown dwarf
Eliminating False Positives
Grazing Eclipsing binaries
Foreground Binary diluted by
faint background star
Secondary is really brown dwarf
-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
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
Orbital Period in days
Siz
e R
ela
tive
to
Ea
rth
Jun
2010
Feb 2011
Planet Candidates as of Dec 2011
Orbital Period in days
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!!
Recommended