JOHANNES KEPLER : JOHANNES KEPLER A guy who’s thought a lot about planets ( By permission Sternwarte Kremsmünster)
Kepler Mission A SEARCH FOR HABITABLE PLANETS : Kepler Mission A SEARCH FOR HABITABLE PLANETS David Koch
NASA Ames Research Center
Ames Internship Program
27 October 2004
OVERVIEW : 3 OVERVIEW What makes for a Habitable Planet
Different Methods for Finding Planets
Planets Discovered to date
Transit Photometry
Kepler Mission Concept
Expected Results
WHAT DOES HABITABLE MEAN TO YOU? : 4 WHAT DOES HABITABLE MEAN TO YOU?
WHAT DOES HABITABLE MEAN TO YOU? : 5 WHAT DOES HABITABLE MEAN TO YOU? Right temperature
Air
Liquid water
Light
Radiation shield
Asteroid protection “This land is your land, and this land is my land
From the California, to the New York island
From the Redwood Forest, to the Gulf Stream waters --
This land was made for you and me.
“As I went walking that ribbon of highway,
I saw above me that endless skyway,
I saw below me that golden valley --
This land was made for you and me.
“I roamed and rambled and I followed my footsteps
To the sparkling sands of her diamond deserts
All around me a voice was sounding --
This land was made for you and me.
“When the sun comes shining and I was strolling
And the wheat fields waving and the dust clouds rolling
The voice was chanting as the fog was lifting
This land was made for you and me.“
Words and music by Woody Guthrie (1940)
THINGS THAT AFFECT TEMPERATURE : 6 THINGS THAT AFFECT TEMPERATURE Want temperature so you can have liquid water on the surface of the planet
Temperature of star
Stellar mass determines temperature and size
type mass temp °K radius
O5 60 42,000 12
B5 5.9 15,200 3.9
A0 2.9 9,790 2.4
F0 1.6 7,300 1.5
G2 (Sun) 1.0 5,790 1.0
K0 0.79 5,150 0.85
M2 0.40 3,520 0.50
STELLAR SIZES AND MASSES : 7 STELLAR SIZES AND MASSES The mass (in solar masses) and radius (in AU) of dwarf stars, also known as main-sequence stars or luminosity class V, are shown in black.
The Sun has a radius of 0.00467 AU and a mass of 1 solar mass.
Giant stars, luminosity class III, of the same spectral type are shown in red.
THINGS THAT AFFECT TEMPERATURE : 8 THINGS THAT AFFECT TEMPERATURE 2. Distance from the star
3. Shape of planet’s orbit
circular or elliptical 4. Planet’s atmosphere
Greenhouse gases These define the Habitable Zone (HZ) for a star
THE HABITABLE ZONE FOR VARIOUS STELLAR TYPES : 9 THE HABITABLE ZONE FOR VARIOUS STELLAR TYPES The Habitable Zone (HZ) in green is the distance from a star where liquid water is expected to exist on the planets surface. (Kasting, Whitmire and Reynolds, 1993)
WHAT IS IMPORTANT ABOUT AN ATMOSPHERE? : 10 WHAT IS IMPORTANT ABOUT AN ATMOSPHERE? Composition (Earth)
free oxygen (about 23%)
mostly inert (about 75% nitrogen)
very little toxic gases
Composition affects temperature
Minimize day-night extremes
Greenhouse gases (water, CO2) hold in the heat
Acts as a shield
Cosmic rays (high energy gamma-rays, protons, electrons)
Solar wind and solar flares (charged particles)
UV - ultraviolet
Micrometeoroids (put a hole through Space Shuttle window)
Transports water
Rain
PLANET SIZE : 11 PLANET SIZE
Planets form by accretion from a disk of gas and dust
Too small (about <0.5 MÅ):
Can’t hold onto a life sustaining atmosphere (Mercury, Mars)
surface gravity g=0.8 G
Too big (about >10 MÅ):
Can hold onto the very abundant light gases (H2 and He) and turn into a gas giant (Jupiter, Saturn, Uranus, Neptune)
surface gravity g=2.2 G
(Surface gravity proportional to radius) Copyright Lynnette Cook Planet size affects habitability
PLANETS IN OUR SOLAR SYSTEM : 12 PLANETS IN OUR SOLAR SYSTEM Terrestrials Gas giants
Mercury Venus Earth Mars Jupiter Saturn Uranus Neptune Pluto mass 0.055 0.82 1.00 0.11 318 95 14 17 .0002
radius 0.38 0.95 1.00 0.53 11.2 9.4 4.0 3.9 0.18
area 0.15 0.90 1.00 0.28 126 89 16 15 0.03
volume 0.06 0.85 1.00 0.15 1408 844 64 59 0.006
density 0.98 0.95 1.00 0.71 0.24 0.12 0.24 0.32 0.20
(all values are relative to Earth)
BOTTOM LINE : 13 BOTTOM LINE Key features for habitable planets
Habitable zone (temperature)
Planet size (mass)
Reference: Rare Earth, Ward and Brownlee, Copernicus (Springer-Verlag) ISBN 0-387-98701
DETECTING EXTRA-SOLAR PLANTS : 14 DETECTING EXTRA-SOLAR PLANTS Meaning of extra-solar
Planets outside our solar system
Or
Planets orbiting other stars
TECHNIQUES FOR FINDING EXTRASOLAR PLANETS : 15 TECHNIQUES FOR FINDING EXTRASOLAR PLANETS Method Yield Mass Limit Status
Pulsar Timing m/M ; t Lunar Successful (3)
Radial Velocity m sini ; t Uranus Successful (~120)
Astrometry m ; t ; Ds ; a
Ground: Telescope Jupiter Ongoing
Ground: Interferometer sub-Jupiter In development
Space: Interferometer Uranus Being studied
Transit Photometry A ; t ; sini=1
Ground sub-Jupiter HD209458, OGLE TR-56
Space Venus Planned Kepler
Reflection Photometry: albedo*A ; t
Space Saturn Planned Kepler
Microlensing: f(m,M,r,Ds,DL )
Ground sub-Uranus On-going
Direct Imaging albedo*A ; t ; Ds ; a ; M
Ground Saturn Being studied
Space Earth Being studied
(Source: J. Lissauer)
SEARCH RESULTS : 16 SEARCH RESULTS The first 50 known extrasolar planets are shown along with the planets in our solar system.
The limit for planet detection using Doppler spectroscopy is shown.
The range of habitable planets (0.5 to 10 MÅ) in the HZ is shown in green.
WE NEED A DIFFERENT APPROACH : 17 WE NEED A DIFFERENT APPROACH Radial velocity (Doppler spectroscopy) method unable to detect Earth-size planets
Earth-like planets are about 300 times less massive and about 100 times smaller in area than Jupiter
Need a different approach that can detect smaller planets
No method exists for detecting habitable planets from ground-based observatories
The Kepler Mission uses photometry to detect transits and can detect Earth-size planets from space
The Kepler Mission is optimized to detect habitable planets in the habitable zone of solar-like stars
USING PHOTOMETRY TO DETECT PLANETS : 18 USING PHOTOMETRY TO DETECT PLANETS Transits
Planet crosses line of sight between
observer and star and blocks
a small amount of light from the star
Different from occultation or eclipse
Occult means to cover over or to hide
Photometry
Method of measuring the amount of light
A light meter on a camera is a simple photometer
USING PHOTOMETRY TO DETECT EARTH-SIZE PLANETS : 19 USING PHOTOMETRY TO DETECT EARTH-SIZE PLANETS The relative change in brightness (DL/L) is equal to the relative areas (Aplanet/Astar)
To measure 0.01% must get above the Earth’s atmosphere
Method is robust but you must be patience:
Require at least 3 transits preferably 4 with same brightness change, duration and temporal separation Jupiter:
1% area of the Sun (1/100) Earth or Venus
0.01% area of the Sun (1/10,000)
GEOMETRY FOR TRANSIT PROBABILITY : 20 GEOMETRY FOR TRANSIT PROBABILITY Not all planetary orbits are aligned along our line of sight to a star
Diameter of Sun d* is about 0.01 AU. Diameter of Earth orbit D is 2 AU
Random probability of detecting a Sun-Earth analog is about 0.5%
So one needs to look at thousands of stars IF all have an Earth
(Ref: Koch & Borucki, Circumstellar Habitable Zones, p229-237, R. Doyle ed., Travis House, 1996)
Kepler MISSION CONCEPT : 21 Kepler MISSION CONCEPT Kepler Mission is optimized for finding
habitable planets ( 0.5 to 10 MÅ )
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
> 4 year duration
Kepler PHOTOMETER : 22 Kepler PHOTOMETER Photometer = CCDs + (Telescope = optics + metering structure)
Kepler will be 9th largest Schmidt ever built
Proto Type CCDs : 23 Proto Type CCDs Views of a prototype module composed of
two CCDs mounted to a common carrier Each CCD is 2200 columns by 1024 rows, thinned, back-illuminated,
anti-reflection coated, 4-phase devices manufactured by e2v.
Each CCD has two outputs with the serial channel on the long edge.
The pixels are 27 m square, corresponding to 3.98 arcsec on the sky.
Kepler SPACECRAFT : 24 Kepler SPACECRAFT (Colors are only meant to represent different sub-systems)
EARTH-TRAILING HELIOCENTRIC ORBIT : 25 EARTH-TRAILING HELIOCENTRIC ORBIT Delta II 2925-10L
FIELD OF VIEW IN CYGNUS : 26 FIELD OF VIEW IN CYGNUS A region of the extended solar neighborhood in the Cygnus-Lyra regions along the Orion arm of our galaxy has been chosen.
DETECTABLE PLANETS FOR V=12 STAR : 27 DETECTABLE PLANETS FOR V=12 STAR The detectable planet size is shown for a nearly central transit as a function of the stellar size and orbit. For a solar-like star (G2V) and a 1 AU orbit a planet somewhat smaller than Earth can be detected. Detections are based on a total SNR >8s and >3 transits in 4 years.
EXPECTED RESULTS : 28 The minimum detectable planet size versus planetary orbital period for a 12th magnitude solar-like star (G2), a CDPP of 20 ppm and >4 grazing transits.
(Ref: Koch et al, , Overview and Status of the Kepler Mission, SPIE Conf 5487,p1491-1500 Optical, Infrared, and Millimeter Space Telescopes, J. Mather ed., Glasgow, Scotland, 2004) EXPECTED RESULTS
EXPECTED RESULTS : 29 EXPECTED RESULTS Hypothesis: all dwarf stars have planets and monitor 100,000 dwarf stars for 4 years
Transits of terrestrial planets:
About 50 planets if most have R~1.0 RÅ (M~1.0 MÅ )
About 185 planets if most have R~1.3 RÅ (M~2.2 MÅ )
About 640 planets if most have R ~2.2 RÅ (M~10 MÅ )
About 70 cases (12%) of 2 or more planets per system
Transits of thousands of terrestrial planets:
If most have orbits much less than 1 AU
Modulation of reflected light of giant inner planets:
About 870 planets with periods ≤1 week, 35 with transits
Albedos for 100 giants planets also seen in transit
Transits of giant planets:
About 135 inner-orbit planet detections
Densities for about 35 giants planets from radial velocity data
About 30 outer-orbit planet detections
Results expected will most likely be a mix of the above
SCHEDULE AND RESULTS : SCHEDULE AND RESULTS 30
SCIENCE TEAM : 31 SCIENCE TEAM William Borucki, Principal Investigator, NASA Ames Research Center
David Koch, Deputy Principal Investigator, NASA Ames Research Center Co-Investigator’s Working Group
G. Basri UC-Berkeley
T. Brown HAO/NCAR
W. Cochran McDonald Obs./U. Texas
E. DeVore SETI Institute
E. Dunham Lowell Observatory
J. Geary SAO
R. Gilliland STScI
A. Gould Lawrence Hall of Sci/UC-B
J. Jenkins SETI Institute
Y. Kondo NASA/GSFC
D. Latham SAO
J. Lissauer NASA/ARC Science Working Group
A. Boss Carnegie Institute of Washington
D. Brownlee University of Washington
J. Caldwell York University
A. Dupree SAO
S. Howell Planetary Science Institute
G. Marcy UC-Berkeley
D. Morrison NASA/ARC
T. Owen University of Hawaii
H. Reitsema Ball Aerospace
D. Sasselov SAO
J. Tarter SETI Institute MANAGEMENT TEAM
Chet Sasaki, Project Manager at Jet Propulsion Lab
Larry Webster, Deputy Project Manager at NASA Ames Research Center
Len Andreozzi, Program Manager Ball Aerospace, Boulder, CO
SUMMARY : SUMMARY The Kepler Mission will:
Observe more than 100,000 dwarf stars
continuously for 4 to 6+ years
with a precision capable of detecting Earth’s in the HZ
The Kepler Mission can discover:
Planet sizes from that of Mars to greater than Jupiter
Orbital periods from days up to two years
About 600 terrestrial planetary systems if most have 1 AU orbits
About 1000 inner-orbit giant planets based on
already known frequency
Can expect 100’s to 1000’s of ??? size planets
depending on frequency ??? and orbit ???
A NULL result would also be very significant ! ! !
Results begin 3 months after launch in Oct. 2007 and
continue for 4 to 6+ years 32
New Yorker Cartoon : New Yorker Cartoon “Well, this mission answers at least one big question: Are there
other planets like ours in the universe?” Drawing by H. Martin; © 1991 The New Yorker Magazine, Inc. 33
Backups : 34 Backups
THINGS THAT AFFECT TEMPERATURE : 35 THINGS THAT AFFECT TEMPERATURE 2. Distance from the star
3. Shape of planet’s orbit
circular or elliptical 4. Planet’s atmosphere
Greenhouse gases These define the Habitable Zone (HZ) for a star 1. Type of star (mass, temperature and size)
MOTIVATION : MOTIVATION • Fundamental human question:
Are we alone? (public)
• Deeper scientific question:
What is the frequency of Earth-size planets? (theory)
• Future space missions:
How to build or not to build TPF? (NASA managers)
• Many others…
• Kepler Mission goals are …
36
Kepler GOALS : Kepler GOALS Explore the structure and diversity of planetary systems.
This is achieved by observing a large sample of dwarf stars to:
1. Determine the frequency of terrestrial and larger planets in or near the habitable zone of a wide variety of spectral types of stars;
2. Determine the distributions of size and semi-major axis of these planets;
3. Estimate the frequency and orbital distribution of planets in multiple-star systems;
4. Determine the distributions of semi-major axis, albedo, size, mass and density of short-period giant planets;
5. Identify additional members of each photometrically discovered planetary system using complementary techniques; and
6. Determine the properties of those stars that harbor planetary systems. 37
ASTROPHYSICAL VALUE OF PHOTOMETRY WITH KEPLER MISSION : 38 ASTROPHYSICAL VALUE OF PHOTOMETRY WITH KEPLER MISSION Stellar Physics Value
Stellar rotation rates Extensive data set
p-mode oscillations Window to stellar interior:
Mass, age, He abundance
Characteristics of solar-type stars Define: What is a "normal" star?
Frequency of Maunder minimums Earth climatic implications, paleoclimatology
Stellar activity Star spot cycles, white light flaring
Astrophysics Value
Cataclysmic Variables Pre-outburst activity, mass transfer
Eclipsing binaries Frequency of high-mass-ratio systems
Active Galactic Nuclei variability "Engine" size in BL Lac, quasars, blazars
(Ref: NASA CP-10148, "Astrophysical Science with a Spaceborne Photometric Telescope")
COMPARISON : 39 COMPARISON My apologies if any number is incorrect or out-of-date
EXTENDED SOLAR NEIGHBORHOOD : 40 EXTENDED SOLAR NEIGHBORHOOD The stars sampled are similar to the immediate solar neighborhood.
Young stellar clusters, ionized HII regions and the neutral hydrogen,
HI, distribution define the arms of the Galaxy.
The view is from the north galactic pole looking down onto the galactic plane
SEARCH SPACE SENSITIVITY : 41 SEARCH SPACE SENSITIVITY The limit of Kepler for planet detection of planets around a solar-like star is shown by the yellow region
Ground based photometry is limited by the Earth’s atmosphere
The range of habitable planets (0.5 to 10 MÅ) in the HZ is shown in green.
BRIEF HISTORY : BRIEF HISTORY • 1952 Struve suggests advantages of photometric detection vs. radial velocity
• 1974 Rosenblatt paper suggesting looking for planetary transits
• 1984 Borucki and Summers paper on transit detection
• 1992 Present concept at Discovery workshop, San Juan Capistrano
• 1994 First Discovery proposal as FRESIP (cost not believable)
• 1996 Second Discovery proposal as Kepler (technically weak)
Conducted CCD testing for next go-round
• 1998 Third Discovery proposal (believed single CCD test, but questioned system performance)
Performed Tech Demo of end-to-end system with transit detection
• 2000 Fourth Discovery proposal (one of three selected for study phase)
• 2001 Dec 21 selected as Discovery mission #10 (DAWN selected as #9) 42
AFTER SELECTION : AFTER SELECTION Delayed phase B startup by one year, but…
Told by Ed Weiler to maintain schedule for CCDs and optics
Told to select either GSFC or JPL to manage the development
After a lot of … , JPL was named as the management center
Kick-off with new team member (JPL) in June 2002
Replanned/recosted program with one-year slip to Oct 2007 launch
System Requirements Review October 2003
Preliminary Design Review October 2003 43
ORGANIZATION CHART : ORGANIZATION CHART We are really organized
or
Really, we are organized 44
KEY PARAMETERS FOR PHOTOMETRIC DETECTION OF EXTRASOLAR PLANETS : 45 KEY PARAMETERS FOR PHOTOMETRIC DETECTION OF EXTRASOLAR PLANETS Duration of a transit:
tc =13 a1/2 M1/4 hrs ~ 13 a1/2 hrs (a in AU)
when crossing the center of the star
Relative brightness change caused by a transit:
DL/L = Ap/A*, area Earth/area Sun = 84 ppm
Probability of seeing a transit:
p = radius of star / radius of orbit = 0.5% r*/a (r* solar radii, a in AU)
Robust but must be patience:
Require at least 3 transits preferably 4
with same brightness change, duration and temporal separation
CONTINUOUSLY VIEWABLE HIGH DENSITY STAR FIELD : CONTINUOUSLY VIEWABLE HIGH DENSITY STAR FIELD One region of high star field density far (>55°) from the ecliptic plane where the galactic plane is continuously viewable is centered at RA=19h22m Dec=44°30’.
The 55° ecliptic plane avoidance limit is defined by the sunshade size for a large aperture wide field of view telescope in space. 46
NUMBER AND DISTANCE OF DWARF STARS FOR WHICH VARIOUS PLANETS CAN BE DETECTED : 47 NUMBER AND DISTANCE OF DWARF STARS FOR WHICH VARIOUS PLANETS CAN BE DETECTED Based on planets in a 1-yr orbit, detection SNR > 8s, transits lasting 80% of central transit duration and monitoring of 100,000 dwarf stars as faint as V=14 for 4 years.
Planets in shorter period orbits have a greater detectability.
PROGRAM PHASES : PROGRAM PHASES Phase A Concept Study (Aug ‘01)
(Mostly done in 4 proposals)
Phase B Engineering solution for all subsystems, cost to complete,
Start long lead procurements
Lock up requirements, System Requirements Rev (SRR) Oct ‘03
Ends with Preliminary Design Review (PDR) Oct ‘04
and Confirmation Review (CR) Dec ‘04
Phase C Detailed design and manufacturing drawings
Ends with Final Design Review (CDR) Oct ‘05
Phase D Fabricate, assemble, test, launch (Oct ‘07) and commission
Phase E Flight operations (4+ years) and scientific data analysis 48
STELLAR CLASSIFICATION PROGRAM : 49 STELLAR CLASSIFICATION PROGRAM Kepler Input Catalog:
Spectroscopic measurements and modeling to determine spectral type and
size for all stars in the FOV with V<15
Identify and eliminate magnetically active, young, unevolved stars
FOLLOW-UP OBSERVING PROGRAM : 50 FOLLOW-UP OBSERVING PROGRAM Eliminate grazing eclipsing binaries and white dwarfs:
Radial velocity measurements to eliminate stellar companions
Determine mass of transiting giant planets:
Radial velocity measurements for M>0.5 MJ
Determine density for transiting giant:
Use measured mass and size
Search for additional non-transiting giant planets in system:
Radial velocity measurements
Determine detailed stellar properties (all stars with planets and for a control set):
Mass, size, distance, metallicity, luminosity, multiplicity (binary, etc.)
Eliminate background objects:
Look in Kepler data for change in point spread function during “transit” due to
background transiting giant planet or eclipsing binary
High spatial resolution image: HST, WST or ground based adaptive optics
POWER SPECTRUM OF SUN FROM SMM DATA FOR 1985-1989 : 51 POWER SPECTRUM OF SUN FROM SMM DATA FOR 1985-1989 The intrinsic brightness fluctuations are expected to range from 10-3 at the rotation period of the star (~weeks) due to the presence of large star spot groups to <10-5 with a duration of hours due to turbulent motions and gravity waves in the stellar photosphere (Fröhlich, 1987).
Brightness changes with durations greater than 16 hours will have little affect on the detectability of transits.
INFORMATION OBTAINED FROM PLANETARY TRANSITS : 52 INFORMATION OBTAINED FROM PLANETARY TRANSITS Planet size:
From relative brightness change and stellar size
Orbital size:
From orbital period and stellar mass using Kepler’s Third Law
Characteristic planet temperature:
From orbit size and stellar luminosity
Frequency of planet formation for broad range of stellar types:
From ensemble of planetary systems
Distribution of planetary sizes, orbital sizes, coplanarity, effects of Jovian planets:
From ensemble of planetary systems
Frequency and orbits of planets in multiple stellar systems (binaries, etc.):
From ensemble of planetary systems
Additional science relating to planet habitability:
Stellar activity (star spot cycles, p-mode oscillations, white light flaring, etc.)
Frequency of Maunder minimums and the implications for the Earth’s climate
Stellar rotation rates and limb darkening
NUMBER OF DWARF STARS FOR WHICH PLANETS CAN BE DETECTED : 53 NUMBER OF DWARF STARS FOR WHICH PLANETS CAN BE DETECTED The solid lines show the number of dwarf stars of each spectral type for which a planet of a given radius can be detected at ≥8s. The conservative numbers are based on 4 near-grazing transits with a 1 yr period and stars with V≤14. The dashed lines show a significant increase in the number of stars when assuming 4 near-central transits with a 1-yr period. An even greater increase is realized for 8 near-grazing transits with a 0.5-yr period.
TRANSIT PROPERTIES FOR SOLAR SYSTEM OBJECTS : 54 TRANSIT PROPERTIES FOR SOLAR SYSTEM OBJECTS Orbital Semi- Transit Transit Geometric Inclination Prob
Period Major Axis Duration Depth Probability Invariant pl sec Det
Planet P (yrs) a (A.U .) (hours) (% ) (%) f (deg) (%)
Mercury 0.241 0.39 8.1 0.0012 1.19 6.33 15
Venus 0.615 0.72 11.0 0.0076 0.65 2.16 23
Earth 1.00 1.00 13. 0.0084 0.47 1.65 22
Mars 1.88 1.52 16 0.0024 0.31 1.71 14
Jupiter 11.86 5.2 30 1.01 0.089 0.39 18
Saturn 29.5 9.5 40 0.75 0.049 0.87 4
Uranus 84.0 19.2 57 0.135 0.024 1.09 2
Neptune 164.8 30.1 71 0.127 0.015 0.72 2
Dependency P2M* = a3 13d*( a/M*)1/2 ∆L/L=Ap/A* d*/D f 4 d*
πf D
Note: M* is in solar masses; Ap is the area of the planet.