Completing the Census
of Exoplanetary
Systems
with WFIRST.
Microlensing 20
Institut d’Astrophysique de Paris
January 15, 2016
Scott Gaudi
Matthew Penny
The Ohio State University
(Penny et al. in prep)
(with the WFIRST SDTs and on behalf of the WFIRST Microlensing SIT)
Planet Formation.
Must understand the physical processes by which micronsized grains in protoplanetary disks grow by 10~13-14 in size
and 10~38-41 in mass.
Hard!
A Complete
Exoplanet
Census.
~1800 Confirmed Planets
~3800 Planet Candidates
Kepler’s
Search Area
M
V
E
M
JS U N
P
Why complete the census?
• A complete census is likely needed to
understand planet formation and evolution.
– Most giant planets likely formed beyond the
snow line.
– Place our solar system in context.
– Water for habitable planets likely delivered
from beyond the snow line.
• Mother nature is more imaginative that we
are.
Why Microlensing?
~1800 Confirmed Planets
~3800 Planet Candidates
Korean Microlensing
Telescope Network.
(Henderson et al. 2014)
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%.
• Resolve 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.
WFIRST.
What is the Wide Field
InfraRed Survey Telescope?
• #1 recommendation of the 2010 Decadal Survey for a
large space mission.
• Notional mission, based on several different inputs,
including:
– JDEM-Omega (Gehrels et al.)
– MPF (Bennett et al.)
– NISS (Stern et al.)
• Three equal science areas:
– Dark energy (SNe, Weak Lensing, BAO).
– Exoplanet microlensing survey.
– GO program including a Galactic plane survey.
WFIRST Designs.
• NASA put together two science definition teams to come
up with “Design Reference Missions”
• Original Science Definition Team (Green et al. arXiv:1208.4012,
arXiv:1108.1374)
- DRM1 (1.3m)
- DRM2 (1.1m)
- AFTA/WFIRST Science Definition Team (Dressler et al. arXiv:
1210.7809, Spergel et al. arXiv:1305.5425, arXiv:1503.03757)
- Studied the application of National Reconnaissance Office (NRO)
telescopes to WFIRST
• Two 2.4m space-qualified telescopes, donated to NASA.
• Mirrors and spacecraft assemblies.
– Also considered a coronagraph and serviceability.
WFIRST-AFTA.
WFIRSTAFTA
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
• 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
Pixel Size
0.11”
• Imaging of debris disks
• 400 – 1000 nm bandpass
Lifetime
5+1 years
• 10-9 contrast
contrast
• 200 milli-arcsec inner working angle
Orbit
L2
Microlensing Simulations.
(Matthew Penny)
(Penny et al. in prep)
(Penny et al., in prep.)
(Penny et al. in prep)
2 ✕ Mass of the Moon @ 5.2
AU
(~27 sigma)
Free floating Mars
(~23 sigma)
Kepler’s
Search Area
WFIRST’s
Search Area
M
V
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M
JS U N
P
(Penny et al. in prep)
Completing the Exoplanet Census.
Together, Kepler and WFIRST complete
the statistical census of planetary systems
in the Galaxy.
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~2600 detections.
Some sensitivity to “outer”
habitable zone planets.
Sensitive to analogs of all
the solar systems planets
except Mercury.
Hundreds of free-floating
planets.
Characterize the majority
of host systems.
Galactic distribution of
planets.
Sensitive to lunar-mass
satellites.
(Penny et al. in prep)
Habitable Planets.
(Penny et al., in prep.)
Free Floating* Planets.
(DiStefano & Scalzo 1999, Han & Kang 2003, Han et
al. 2005, Strigari et al. 2012)
• Solivagant or widelyseparated planetary-mass
objects can act as isolated
lenses.
• Short timescales, ultimately
limited by source size.
• Solivagant planets are a
generic prediction of
dynamical evolution of
planetary systems.
• May also be formed via direct
collapse or more exotic
mechanisms.
*Also known as “Rogue Planets”, “Solivagant Planets”, or “Nomads”.
Free Floating Planets.
• Excess of short time scale
events relative to expected
stellar/brown dwarf
contribution.
• Unbound or wide-separation
planets.
• Implies roughly 2 Jupitermass free-floating planets
per star.
• If free-floating and originally
formed in planetary systems,
hard to explain.
(Sumi et al. 2011; MOA + OGLE)
(Penny et al., in prep)
WFIRST-AFTA will measure the compact object mass function over at least 8
orders of magnitude in mass (from Mars to ~30 solar masses).
WFIRST
+
Coronagraph
Exoplanet Direct Imaging
WFIRST will:
Spectra at R=70
easily distinguishes
between a Jupiterlike and Neptune-like
planet at 2 AU about
stars of different
metallicity.
• 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.
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
2600 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”
WFIRST 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.
Potential of the WFIRST
Microlensing Survey.
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Mass and distance measurements of the host stars and planetary systems.
– Parallax (orbital, satellite), lens flux, finite source effects, relative lens-source proper
motion, astrometric microlensing, source parallax, lens parallax, …
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Characterization of a (subset) of the host stars
– JWST NIRSpec can estimate Teff and [M/H] with R~2700 for KAB<20 hosts.
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Constraints on orbital elements.
Multiple planet systems.
Planets in binaries, including circumbinary planets.
Free-floating planets.
Moons of planets.
Transiting planets.
Other astrophysics. (KBOs, astroseismology, etc.)
…. ??
• All of these potential applications need to be studied!
To Do.
• Improve our understanding of microlensing event rates:
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Refine Galactic models.
Event rates, near-IR microlensing survey.
Optical and Near-IR luminosity function.
Measure the Galactic distribution of planets (Spitzer, K2).
• Optimize the survey strategy
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Field location, number, and cadence.
Optimize number and choice of filters.
Contemporaneous ground and space-based observations.
Alerts on events (?)
• Determine the precision of the measured event parameters.
– Verify lens flux method of measuring masses (Spitzer, K2 + AO follow-up)
• Determine hardware, software, and calibration requirements.
• Identify and carry out needed precursor observations.
• Develop data reduction and analysis tools.
Is WFIRST Real?
• Yes!
• FY16 appropriation provides $90M for
WFIRST (+$76M more than OMB request)
and directs NASA to start formulation.
• New start (KDP-A) in February 2016.
• WFIRST Science Investigation Team
Proposals were due on October 15, selected
proposals announced on December 17.
Courtesy of Paul Hertz
WFIRST Microlensing
Science Investigation Team.
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Scott Gaudi (PI)
David Bennett (Deputy PI)
Jay Anderson
Chas Beichman
Geoff Bryden
Sebastiano Calchi Novati
Sean Carey
Dan Foreman-Mackey
Andy Gould
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Calen Henderson
David Nataf
Matthew Penny
Radek Poleski
Yossi Shvartzvald
Keivan Stassun
Rachel Street
Jennifer Yee
The Microlensing Watershed.
• Spitzer & K2C9.
– Masses and distances.
– Mass function and Galactic
distribution of planets.
– Free-floating planets
masses (K2C9).
• KMTNet
– ~50 detections/year.
• Euclid & WFIRST
– Detections en masse.
– Complete the census of
exoplanets started by Kepler.
(Udalski et al. 2014; Yee et al. 2014, 2015;
Calchi Novati et al. 2014, 2015; Zhu et al.
2015a,b,c; Shvartzvald et al. 2015; Street et al.
2015; Poleski et al. 2015; Henderson et al.
2015; Bozza et al. 2016)
Why Spitzer and K2C9 is
Important for WFIRST.
• Practical application of methods to infer masses and
distances.
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Range of Earth-satellite baselines.
Free-floating planets.
Ensemble statistical analyses.
Verify the primary method of measuring masses with WFIRST.
Continuous, uniform photometry.
Crowded field photometry reduction techniques.
First wide-field IR microlensing survey.
Event selection for follow-up.
Inform field selection for WFIRST.
NASA is investing heavily in these campaigns.
Range of Separations.
Spitzer
K2C9
(Gould’s Talk)
WFIRST-AFTA @ L2
Kepler vs. WFIRST-AFTA at L2
The Need for IR
Measurements.
Building the microlensing
community.
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The current microlensing community is simply too small to accomplish all of
the work needed for the upcoming missions (Spitzer/K2C9/Euclid/WFIRST).
Much of the work for these missions requires image reduction and analysis
techniques.
– K2C9, Spitzer, ground-based observations.
– “Introduce” newcomers with expertise in these areas, then induct them into the cult of
microlensing.
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Inducting and maintaining cult members:
– Open data policies.
– Open source modeling software.
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NASA is actively exploring international partnerships and participation.
• We are no longer a parochial cult: we must seize this
opportunity, and maintain and build on the momentum.