The valley network channels on the heavily cratered ancient surface of Mars suggest the presence of liquid water ~3.8 Gyr ago. However, the implied warm climate is difficult to explain in the context of the standard solar model, even allowing for the maximum CO2 greenhouse heating. In this paper we investigate the astronomical and planetary implications of a nonstandard solar model in which the zero-ago, main-sequence Sun had a mass of 1.05¿0.02 M⊙. The excess mass was subsequently lost in a solar wind during the first 1.2-0.20.4 Gyr of the Sun's main sequence phase. The implied mass-loss rate of 4+3-2¿10-11 M⊙yr-1, or about 103¿ that of the current Sun, may be detectable in several nearby young solar type stars. ¿American Geophysical Union 1995