Results illustrated under varying assumptions of the initial hydrodynamic escape onset time, t₀, within the context of the slow rotator scenario. Each circle represents a ‘matched case’; namely, a scenario that satisfies the constraints from three isotopic ratios of Ne and Ar in Venus’ atmosphere. The colour bar indicates the timescale required for the complete loss of hydrogen. All cases shown correspond to scenarios with no residual H₂ in the secondary atmosphere. The variable t₀ represents the time, in million years (Myr), at which the EUV-driven hydrodynamic escape begins. The dashed line marks an initial H₂O inventory of 1.05×10⁴ moles/cm² and an initial CO₂ inventory of 2.3×10³ moles/cm² (approximately equivalent to 90 bars of CO₂ on present Venus). Matched cases above the dashed line assume an initial CO₂ inventory higher than the present value, while those below assume a lower initial CO₂ inventory.