GJ9827: Mass constraints of a benchmark system from Spitzer transit timing measurements

Presenter: John LIVINGSTON
At 30 pc, the nearby planetary system GJ9827bcd is one of the most promising targets for the characterization of a system of multiple transiting super-Earths. An essential precursor to atmospheric studies is the measurement of the fundamental planet properties, mass, radius, and bulk composition. Ground-based radial velocity (RV) measurements have already yielded the mass of the inner planet, but the masses of the outer two planets in the system have so far eluded detection. We present new Spitzer space telescope observations with which we measure precise transit times, enabling dynamical constraints via transit timing variations (TTVs). In particular the outermost planet shows large amplitude TTVs, which enable the dynamical mass measurement of a small planet which has so far eluded RV detection. These new measurements greatly enhance the prospects for future atmospheric characterization of the system with JWST.