Exoplanet Science with WFIRST

(and why the success of K2C9 is essential for WFIRST)

K2SciConNovember 5, 2015

Scott GaudiThe Ohio State University

The Microlensing Watershed.

• Spitzer & K2C9.– Masses and distances.

– Mass function and Galactic

distribution of planets.

– Free-floating planets

masses (K2C9).

• KMTNet– 60 detections/year.

• Euclid & WFIRST– Detections en masse.

– Complete the census of

exoplanets started by Kepler.

(Udalski et al. 2014, Yee et al. 2014, Calchi Novati et al. 2014, Zhu et al. 2015)

Korean Microlensing Telescope Network.

(Henderson et al. 2014)

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 considers a coronagraph and serviceability.

WFIRST-AFTA.

WFIRST-AFTA

Eff. Aperture 2.28m

FOV 0.281 deg2

Wavelengths 0.7-2 μm

FWHM@1μm 0.10”

Pixel Size 0.11”

Lifetime 5+1 years

Orbit Geosynch.

Wide-Field Instrument

• Imaging & spectroscopy over 1000's sq deg.

• Monitoring of SN and microlensing fields

• 0.7 – 2.0 micron bandpass

• 0.28 sq deg FoV (100X JWST FoV)

• 18 H4RG detectors (288 Mpixels)

• 4 filter imaging, grism + IFU spectroscopy

Coronagraph

Imaging of ice & gas giant exoplanets

• Imaging of debris disks

• 400 – 1000 nm bandpass

• 10-9

contrast

• 200 milli-arcsec inner working angle

Wide-Field Instrument

• Imaging & spectroscopy over 1000's sq deg.

• Monitoring of SN and microlensing fields

• 0.7 – 2.0 micron bandpass

• 0.28 sq deg FoV (100X JWST FoV)

• 18 H4RG detectors (288 Mpixels)

• 4 filter imaging, grism + IFU spectroscopy

Coronagraph

Imaging of ice & gas giant exoplanets

• Imaging of debris disks

• 400 – 1000 nm bandpass

• 10-9

contrast

• 200 milli-arcsec inner working angle

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.– Low-magnification events.– Isolate light from the lens star.

• Visibility.– Complete coverage.

• Smaller systematics.– Better characterization.– Robust quantification of

sensitivities.

SpaceGround

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.

Microlensing Simulations.(Matthew Penny)

(Penny et al., in prep.)

Microlensing Simulations.(Matthew Penny)

(Penny et al., in prep.)

(Penny et al., in prep.)

Free floating Mars

(~23 sigma)

2 ✕ Mass of the Moon @ 5.2 AU

(~27 sigma)

(Penny et al., in prep.)

M

V

E

M

J S U N P

Kepler’s

Search Area

M

V

E

M

J S U N P

Kepler’s

Search Area WFIRST’s

Search Area

(Penny et al. in prep)

Exoplanet Demographics with WIFRST-AFTA.

• ~2600 detections.

• 370 Earths mass and below.

• 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.

Together, Kepler and WFIRST-AFTA complete the statistical census of

planetary systems in the Galaxy.

Habitable Planets.

(Penny et al., in prep.)

Free Floating* Planets.• Solivagant or widely-separated

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”.

(DiStefano & Scalzo 1999, Han & Kang 2003, Han et al. 2005, Strigari et al. 2012)

Free Floating Planets.

• Excess of short time scale

events relative to expected

stellar/brown dwarf

contribution.

• Unbound or wide-

separation planets.

• Implies roughly 2 Jupiter-

mass free-floating planets

per star.

• If free-floating, hard to

explain.

(Sumi et al. 2011; MOA + OGLE)

WFIRST-AFTA will measure the compact object mass function over at least 8 orders of magnitude in mass (from Mars to ~30 solar

masses).

(Pe

nn

y e

t al.,

in p

rep

)

WFIRST+

Coronagraph

Exoplanet Direct ImagingWFIRST will:• 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.

Spectra at R=70 easily distinguishes

between a Jupiter-like and Neptune-

like planet at 2 AU about stars of

different metallicity.

Exoplanet Science with

WFIRST.

WFIRST+C Exoplanet Science

Microlensing Survey High Contrast Imaging

Monitor 200 million Galactic bulge stars every 15 minutes for 1.2 years

2600 cold exoplanets

300 Earth-mass planets

40 Mars-mass or smaller planets

40 free-floating Earth-mass planets

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

Detailed characterization of up to a dozen giant planets.

Discovery and characterization of several Neptunes

Detection of massive debris disks.

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.

Complete the

Exoplanet Census

Discover and Characterize

Nearby Worlds

• 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 atmospheres?

Toward the “Pale Blue Dot”

Microlensing Survey High Contrast Imaging

• 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.

• 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.

WFIRST will lay the foundation for a future flagship direct imaging mission capable of detection and

characterization of Earthlike planets.

Science and technology foundation for the New

Worlds Mission.

Courtesy of Jim Kasting.

Guest Investigator Science.

• HST aperture with ~200✕ the FOV.

• Archival science in bulge, SNe and HLS surveys.

• ~25% of time to GO programs.

High Latitude Survey ~2000 sq. degrees in four filters +

slitless grism spectrscopy.

Why K2C9?

Science from K2C9.

• Bound planet and free-floating planets masses and distances.– Mass function and Galactic distribution of

planets.• Detections from both K2 and the ground.• Free-floating planet masses• Free-floating versus widely separated

masses (with follow-up).

Why is K2C9 Essential for WFIRST-AFTA?

Why K2C9 is Important for WFIRST.

• Practical application of methods to infer masses and distances.– Range of Earth-satellite baselines.

– Free-floating planets.

– Ensemble statistical analyses.

• Continuous photometry– K2 discovers planetary signals not found from the ground.

• Crowded field photometry reduction techniques.

• First wide-field IR microlensing survey.

• Event selection for follow-up.

• Inform field selection for WFIRST.

• Verify the primary method of measuring masses with WFIRST.

• Help!

Range of Separations.

Spitzer K2C9

(Gould’s Talk)

WFIRST-AFTA @ L2

Kepler vs. WFIRST-AFTA at L2

The Need for IR Measurements.

Building the US microlensing community.

• The current US microlensing community is simply

too small to accomplish all of the work needed for

the upcoming missions (Spitzer/K2C9/WFIRST).

• Much of the work for K2C9 requires image reduction

and analysis techniques.– K2C9, DECam, IR observations.

– “Introduce” newcomers with expertise in these areas,

induct them into the cult of microlensing.

• Completely “US-lead” microlensing project.– Open data policy will encourage “adventurers”.

Summary.• The demographics of planets beyond the snow line provides crucial

constraints on planet formation theories.

• Understanding habitability likely requires a broad picture of exoplanet

demographics.

• WFIRST will complete the census begun by Kepler, and will

revolutionize our understanding of cold planets.

• Will enable qualitatively new, exciting science: sub-Earth-mass planets,

free-floating planets, outer habitable zone planets, mass measurements.

• WFIRST will have a broad range of science applications beyond

exoplanets and dark energy, enabled by a large GO program.

• K2C9 is important for the building the microlensing community, and for

WFIRST.