Exoplanet Science
with
WFIRST-AFTA
Microlensing 18
Scott Gaudi
Matthew Penny
The Ohio State University
Kepler is revolutionizing our understanding of exoplanets here!
Ground-based Surveys.
• Ground-based surveys
only sensitive to masses
greater than ~Mearth.
• Narrow range near near
peak sensitivity, roughly
1-4 times the snow line.
• Only sensitive to giant
free-floating planets.
Earth Mass and Below?
• Monitor hundreds of millions of bulge stars
continuously on a time scale of ~10 minutes.
– Event rate ~10-5/year/star.
– Detection probability ~0.1-1%.
– Shortest features are ~30 minutes.
• Relative photometry of a few %.
– Deviations are few – 10%.
• Main sequence source stars for smallest planets.
• Masses: resolve background stars for primary mass
determinations.
Ground vs. Space.
• Infrared.
– More extincted fields.
– Smaller sources.
• Resolution.
Ground
Space
– Low-magnification events.
– Isolate light from the lens star.
• Visibility.
– Complete coverage.
• Smaller systematics.
– Better characterization.
– Robust quantification of
sensitivities.
The field of microlensing event
MACHO 96-BLG-5
(Bennett & Rhie 2002)
Science enabled from space: sub-Earth mass planets,
habitable zone planets, free-floating Earth-mass planets,
mass measurements.
History.
•
NASA Proposals (GEST/MPF) – PI David Bennett.
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–
•
Decadal Survey White Papers:
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–
•
–
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Top Decadal Survey recommendation for a large space mission (Dark Energy, Exoplanets,
Galactic Plane, GO Program)
Science Definition Team – DRM1 and DRM2
No funding until JWST is launched (~2017).
National Reconnaissance Office (NRO) telescopes.
–
–
–
•
Bennett et al. “A Census of Exoplanets in Orbits Beyond 0.5 AU via Space-based
Microlensing”
Gould, “Wide Field Imager in Space for Dark Energy and Planets”
Wide-Field Infrared Survey Telescope (WFIRST).
–
•
Submitted to Midex in 2001, Discovery in 2000, 2004, 2006
Not selected.
Two 2.4m space-qualified telescopes, donated to NASA.
Mirrors and spacecraft assemblies.
SDT formed to assess use for WFIRST, consider a coronagraph and serviceability.
Euclid.
–
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ESA M class Dark Energy Mission
Microlensing is not part of the core science.
WFIRST-2.4
AFTAWFIRST
Wide-Field Instrument
• Imaging & spectroscopy over 1000's sq
deg.
• Monitoring of SN and microlensing fields
Eff. Aperture
2.28m
FOV
0.281 deg2
Wavelengths
0.7-2 μm
• 4 filter imaging, grism + IFU
spectroscopy
FWHM@1μm
0.10”
Coronagraph (descopeable)
Pixel Size
0.11”
• Imaging of debris disks
• 0.7 – 2.0 micron bandpass
• 0.28 sq deg FoV (100X JWST FoV)
• 18 H4RG detectors (288 Mpixels)
• Imaging of ice & gas giant exoplanets
• 400 – 1000 nm bandpass
Lifetime
5 years +?
• 10-9 contrast
• 200 milli-arcsec inner working angle
Orbit
Geo (?)
Comparing Designs.
Euclid
(Opt/NIR)
WFIRST
DRM1
WFIRST
DRM2
AFTAWFIRST
Eff. Aperture
1.13m
1.3m
1.1m
2.28m
FOV
0.44 deg2
0.375 deg2
0.585 deg2
0.281 deg2
Wavelengths
RIZ/YJH
0.92-2.4 μm
0.92-2.4 μm
0.93-2 μm
FWHM@1μm
0.21”
0.19”
0.23”
0.10”
Pixel Size
0.1”/0.3”
0.18”
0.18”
0.11”
Time
0 (300d)
432d
266d
432d (?)
Lifetime
6 years
5 years
3 years
5+1 years +?
Orbit
L2
L2
L2
Geo ?
Hardware
Yields.
• Yields scale with:
– Yield ~propto total observing time
– Yield ~propto number of stars
– Yield ~propto (photon rate)α , with α~0.3 to 1.
• Primary hardware dependencies:
–
–
–
–
–
FOV.
Aperture.
Bandpass (total throughput + red cutoff).
Resolution (background).
Pointing constraints.
• Secondary hardware dependencies:
– Data downlink, slew and settle
Microlensing Simulations.
(Matthew Penny)
Mercury @ 2.2 AU
(~28 sigma)
Free floating Mars
(~23 sigma)
Bound
F.F. Earth
Predicted Planet Yields.
M/MEarth
Euclid
DRM1
DRM2
AFTAWFIRST
0.1
10
30
21
39
1
66
239
176
301
10
197
794
599
995
100
144
630
484
791
1000
88
367
272
460
10,000
41
160
121
201
Total
546
2221
1676
2787
Euclid
DRM1
DMR2
WFIRST-2.4
5
33
27
41
All yields by Matthew Penny.
Exoplanet Demographics with WIFRST.
Together, Kepler and WFIRST
complete the statistical census of
planetary systems in the Galaxy.
WFIRST will:
•
•
•
•
•
Detect 2800 planets, with
orbits from the habitable
zone outward, and masses
down to a few times the
mass of the Moon.
Have some sensitivity to
“outer” habitable zone
planets (Mars-like orbits).
Be sensitive to analogs of all
the solar systems planets
except Mercury.
Measure the abundance of
free-floating planets in the
Galaxy with masses down to
the mass of Mars
Characterize the majority of
host systems.
WFIRST/2.4
Search Area
Kepler
Search Area
Exoplanet Demographics with WIFRST.
Together, Kepler and WFIRST
complete the statistical census of
planetary systems in the Galaxy.
WFIRST will:
•
•
•
•
•
Detect 2800 planets, with
orbits from the habitable
zone outward, and masses
down to a few times the
mass of the Moon.
Have some sensitivity to
“outer” habitable zone
planets (Mars-like orbits).
Be sensitive to analogs of all
the solar systems planets
except Mercury.
Measure the abundance of
free-floating planets in the
Galaxy with masses down to
the mass of Mars
Characterize the majority of
host systems.
Synergy with JWST!!
WFIRST
+
Coronagraph
Exoplanet Direct Imaging
WFIRST-2.4 will:
Spectra at R=70
easily distinguishes
between a Jupiterlike and Neptune-like
planet at 2 AU about
stars of different
metalicity.
• Characterize the spectra of
roughly a dozen radial
velocity planets.
• Provide crucial information
on the physics of planetary
atmospheres and clues to
planet formation.
• Respond to decadal survey
to mature coronagraph
technologies, leading to
first images of a nearby
Earth.
Debris Disk Imaging
WFIRST/2.4 will:
•
•
•
Measure the amount and
distribution of circumstellar
dust,
Measure the large scale
structure of disks, revealing
the presence of asteroid
belts and gaps due to unseen
planets., Measure the size
and distribution of dust
grains,
Provide measurements of
the zodiacal cloud in other
systems.
Debris disk around the young (~100
Myr), nearby (28 pc) sun-like (G2
V0) star HD 107146
http://hubblesite.org/newscenter/archive/releases/2004/33/image/c/
Guest Investigator Science.
23.0
23.5
24.0
24.5
25.0
25.5
26.0
26.5
27.0
27.5
28.0
0.8
i
39
VIS
r 13
39
0.6
z
39
1.0 1.2
1.6
F106
F129 F158
12
12 14
y
39
LSST (10 yr, S Hemisphere, AM 1.2)
WFIRST (1.6k deg 2/yr, ref
zodi)
Euclid (15-20k deg 2, b=45o)
J
H
Y
31
30 30
Sensitivities of LSST, WFIRST, and Euclid
g
39
Labels indicate PSF
half light radius in
units of 0.01 arcsec
u
39
0.4
l (mm)
F184
14
2.0
High Latitude Survey ~2000 sq.
degrees in four filters + slitless
grism spectrscopy.
• HST aperture with
~200✕ the FOV.
• Archival science
in bulge, SNe and
HLS surveys.
• ~25% of time to
GO programs.
mag)
(AB
threshold
src
5s pt
To Do.
• HST imaging of target fields.
• Spitzer/Kepler monitoring of
microlensing events.
• HST follow-up of planet detections.
• H-band ground-based microlensing
survey.
• Manpower!
Summary.
• The demographics of planets beyond the snow line
provides crucial constraints on planet formation
theories and habitability.
• AFTA-WFIRST enables qualitatively new, exciting
science: sub-Earth-mass planets, free-floating
planets, outer habitable zone planets, mass
measurements.
• AFTA-WIFRST will complete the census begun by
Kepler, and will revolutionize our understanding of
cold planets.
• But, lots to do!
Exoplanet
Science with
WFIRST.
WFIRST+C Exoplanet Science
The combination of microlensing and direct imaging will dramatically expand our
knowledge of other solar systems and will provide a first glimpse at the planetary
families of our nearest neighbor stars.
Microlensing Survey
High Contrast Imaging
Monitor 200 million Galactic bulge stars every 15 minutes for
1.2 years
Survey up to 200 nearby stars for planets and debris disks at
contrast levels of 10-9 on angular scales > 0.2”
R=70 spectra and polarization between 400-900 nm
2800 cold exoplanets
300 Earth-mass planets
40 Mars-mass or smaller planets
40 free-floating Earth-mass planets
Complete the
Exoplanet Census
Detailed characterization of up to a dozen giant planets.
Discovery and characterization of several Neptunes
Detection of massive debris disks.
•
How do planetary systems form and
evolve?
•
What are the constituents and dominant
physical processes in planetary
atmospheres?
•
What kinds of unexpected systems
inhabit the outer regions of planetary
systems?
•
What are the masses, compositions, and
structure of nearby circumstellar disks?
•
Do small planets in the habitable zone
have heavy hydrogen/helium
Discover and
Characterize Nearby
Worlds
Toward the “Pale Blue Dot”
WIFRST will lay the foundation for a future flagship direct imaging mission
capable of detection and characterization of Earthlike planets.
Microlensing Survey
• Inventory the outer parts of planetary systems, potentially
the source of the water for habitable planets.
• Quantify the frequency of solar systems like our own.
• Confirm and improve Kepler’s estimate of the frequency of
potentially habitable planets.
• When combined with Kepler, provide statistical constraints
on the densities and heavy atmospheres of potentially
habitable planets.
High Contrast Imaging
• Provide the first direct images of planets around our
nearest neighbors similar to our own giant planets.
• Provide important insights about the physics of planetary
atmospheres through comparative planetology.
• Assay the population of massive debris disks that will
serve as sources of noise and confusion for a flagship
mission.
• Develop crucial technologies for a future mission, and
provide practical demonstration of these technologies in
flight.
Science and technology
foundation for the New
Worlds Mission.
Courtesy of Jim Kasting.