The Sun hangs low on the horizon above solidified pancake ice in the Arctic Ocean. (Photograph courtesy Andy Mahoney, NSIDC.) The moons of Jupiter and Saturn, such as Europa and

Reflected total normalized flux πFn (left panel) and signed degree of linear polarization Ps (right panel) as functions of the planetary phase angle α and wavelength λ for our Hadean:

Schematic illustration of our proposed carbon cycle on early Mars. Evaporation of water (pink shading) from subsurface pore spaces initially deposits siderite, which sequesters atmospheric CO2 (black downward arrow). Increasing

A: XRF maps of Ca, Fe, and Mn; RGB map of U, Mn, and Fe. Calcite and detrital minerals can be distinguished by areas of high and low abundance in