Whipple: A Space-Based Occultation Survey of the Outer Solar System Matthew J. Lehner Harvard-Smithsonian Center for Astrophysics

Proposed Discovery Mission for Survey of Outer Solar System Smithsonian Astrophysical Observatory Ball Aerospace Jet Propulsion Laboratory

Collaborators Charles R. Alcock Len Andreozzi Roger J. Brissenden James L. Fanson Kathryn A. Flanagan Ronald L. Gilliland Matthew J. Holman Almus T. Kenter SAO Ball JPL MIT STScI Scott J. Kenyon Ralph P. Kraft Matthew J. Lehner Harold F. Levison Stephen S. Murray Irene L. Porro Paul R. Weissman Michael W. Werner SAO HCO SwRI MIT JPL

Survey Goals: Measure size distribution of KBOs down to 300 m Map out spatial distribution of Kuiper Belt Determine if a Sedna-like population exists Determine number and distribution of objects in Inner and Outer Oort Clouds Whipple will expand horizon of Solar System science from ~100 AU out to 20,000 AU!

KBO Size Distribution

Sedna Population? Perihelion at 70 AU Mass ~10-3 Earth mass How did it get there? Encounter with passing star Extra-solar planet exchanged with star in birth cluster? What else is out there? Brown et al. (2004) estimate 5 Earth masses! Population formed while Sun in birth cluster? (Morbidelli & Levison, 2006; Brasser et al. 2006) Credit: NASA/JPL-Caltech/R. Hurt (SSC-Caltech)

Occultations of stars 3 km KBO at 43 AU 10 km

10 km object at 10000 AU with a V=14 F0V star Occultations of stars 10 km object at 10000 AU with a V=14 F0V star Point source star 40 Hz sampling Finite source star Added noise

Occultations of stars 3 km at 42 AU, 40 Hz 10 km at 104 AU, 5 Hz

Spacecraft based on Kepler design 95 cm Schmidt optical system 100 square degree field of view Articulated solar arrays Hybrid CMOS focal plane array (Rockwell HyViSI/Hawaii-2RG) 140,000 stars, 40 Hz readout

Fields at all ecliptic longitudes and latitudes Whipple will go into an Earth-trailing orbit, similar to Kepler. Fields at all ecliptic longitudes and latitudes

Hawaii-2RG Hybrid CMOS 36 units of 2048×2048 pixels, 18µm bump-bond every other pixel, get 1024×1024 36µm pixels read out 3×3 aperture around each target star each CMOS device is capable of reading out 4096 sub-apertures devices packaged into 2×2 arrays

FPUs placed on curved focal plane Field flatteners added to surface of each FPU to provide uniform PSF across focal plane Readout controllers placed directly behind focal plane Low power devices, no thermal problems

Data Rate Raw data rate of ~1Gbps Downlink capability ~5Gb per day 5×1011 measurements per day Can only download 10,000 events per day Need significant on-board processing Use field programmable gate arrays (FPGAs)

FPGA Analysis Use “equivalent width” algorithm (Roques et al. 2003) Easily implemented in FPGA

Data Flow Focal plane Instrument Control Computer SIDECAR™ ASIC Solid state recorder Ring buffer Downlink FPGA Ground-based analysis

Expected Event Rates

Expected Event Rates Oort Cloud: 1012 objects (D>3 km) each in Inner and Outer Oort Clouds N(D) ~ D-1.8 randomized eccentricities Sednas: same assumptions as in Oort Cloud 100 AU < a < 1000 AU q > 30 AU