Spitzer Space Telescope Spitzer Meets K2 M.Werner, J.Livingston, V.Gorjian, JPL/Caltech; C.Beichman, D.Ciardi, J.Christiansen, R.Akeson, NExSci; J.Krick, SSC; I.Crossfield, U.Arizona; J.Schlieder, NASA-Ames; H.Knutson, B.Benneke, I.Wong, E.Petigura, K.Deck, Caltech

Spitzer Space Telescope Overview of Spitzer Meets K2 450 Hour Cycle 11 Spitzer GO Proposal –Main thrust is K2 candidate exoplanets around late stars –Our team screens and selects candidates for Spitzer study –4.5um is wavelength of choice Have scheduled/executed 20 observations through K2 field 2 –16 exoplanets, 13 stars –First results to be reported here [Beichman et al, Benneke et al] M ain science thrusts - Improved transit parameters based on better sampling, reduced limb brightening and higher S/N –Improved timing for JWST and other recovery followup –Search for TTVs

Spitzer Space Telescope Nominal Temperatures and Radii of Spitzer Meets K2 Exoplanet Targets

Spitzer Space Telescope Stellar Colors and Exoplanet Orbital Radii for K2 Sample

Spitzer Space Telescope Measured Transits for Two Planets Orbiting K2-3 an M0 Star with [4.5] = 8.4 K2-3b Radius = 2.04 Rearth Transit depth =.0012 T = 800K K2-3d Radius = 1.53 Rearth Transit depth = T = 300K

Spitzer Confirmation of the Transiting Habitable Zone Super-Earth K2-18b – Bjoern Benneke K2-18b is the first habitable zone exoplanet amenable to atmospheric characterization Only two transits observed by K2 Earth: 1370 W/m 2 K2-18b: 1300 W/m 2 K2-18

Spitzer Detection of Third Transit Transit occurs 7σ (1.8 hours) before predicted transit time! Spitzer transit will constrain eclipse/planet geometry much more effectively than did the K2 observations alone. Predicted mid-transit time based on K2 (Montet et al. 2015)

Global Analysis of K2 + Spitzer Photometry Previously unidentified outlier in K2 data led to inaccurate ephemeris No TTV K2 Spitzer

K2-18b would have been lost for future characterizations Long observation time possible from Spitzer facilitated recovery Ephemeris from K2 could have led to non-detections with HST and JWST

Spitzer Space Telescope Summary of Initial Results Spitzer at 4.5um confirms K2 measurements of transit depths for exoplanets K2-3 b,c,d; K2-18b; and b Further analysis of Spitzer data will provide improved constraints on transit geometry and exoplanet properties for these and other systems, including small HZ planets –TTV analysis of K2-3 system in process by Kat Deck, results to be included in Beichman et al paper First round of Spitzer measurements reduce uncertainty in transit times for JWST era. Most dramatically, the transits of K2-18b will occur ~six hours earlier at the time of the JWST launch than K2 ephemeris alone would predict

Spitzer Space Telescope K2-3b is a Promising Target for JWST Spectroscopy Simulations by Mike Line and Tom Greene of the JWST transmission spectrum of K2-3b for several atmosphere models

Spitzer Space Telescope Conclusions Spitzer followup of K2 promises to be very productive scientifically and to set the stage for JWST Observations of K2-3, K2-18b, & b have: Confirmed transit depths Provided better data for exoplanet characterization Improved ephemerides for JWST work Future plans 8 additional exoplanets already queued up for observation Several hundred hours still to be scheduled – we invite suggestions of targets we may overlook Program expanded to include FGK stars Extend Spitzer through Senior Review to go beyond K2 field 5

Spitzer Space Telescope K2 Exoplanets observed or currently planned for observation with Spitzer K2-22b