Revisiting and refining the model of TRAPPIST-1 with Spitzer

With the Spitzer Space Telescope, we have discovered a system of seven transiting planets about the star TRAPPIST-1, and for the first time measured the densities of three Earth-sized, temperate exoplanets using transit-timing variations (Gillon et al. 2017; Ducrot et al. 2018; Grimm et al. 2018). We propose to gather additional transits of the TRAPPIST-1 system, focusing on the outer planets in the system which have had fewer transits observed to date. The four-fold goals of this proposal are: i). to flag potential transits which might be affected by stellar variability; ii). to constrain the dynamical state of the planet system; iii). to better constrain the masses of the planets; iv). to tighten the ephemeris forecast for observations with JWST. In addition, we will search for any evidence an eighth planet, characterize the stellar variability, and forecast planet-planet overlaps during transits. The proposed observations contain measurements which are only possible in March-April 2019, and so we request a time critical review to the extent possible.