17094

Highly irradiated gas-giant exoplanets vigorously lose their atmospheres. This makes them excellent laboratories for extreme atmospheric physics - where we can study the effect of high levels of irradiation and stellar wind. Despite decades of observations with HST comma the scientific value of the Lyman-alpha detections remains surprisingly under-exploited. In particular comma the observations have not yet been able to precisely quantify planetary mass-loss rates. To address the gap between Lyman-alpha models and observations comma a new observational pathway has been proposed to untangle the web of parameter interdependency. Originally identified in the 3D radiative-hydrodynamic simulations comma this method requires measuring the second Lyman-alpha transits that are predicted to occur for hot Jupiters after the main transit. Second Lyman-alpha transits have never yet been probed or observed comma despite this theoretical prediction. By measuring the time-delay of the secondary transit comma the strength of the acceleration mechanism and the inertia of the outflowing gas can be measured comma which is set by the mass loss rate. Thus comma a measurement of a hot Jupiter.s secondary transit will allow us to break the degeneracies that have plagued interpretation of Lyman-alpha transits comma bringing firm physical constraints which will finally allow us to observationally comma qualitatively constrain the mass-loss rate of an exoplanet.