Abstract
IP WE have observed a significant anti-correlation between solar activity and the brightnesses of two Solar System objects. Both the planet Neptune and Saturn's satellite Titan increased in brightness by several per cent between 1972 and 19761 and subsequently became fainter by comparable amounts2. This period corresponds to the decline of solar activity at the end of solar cycle 20 (1972–76), followed by the rapid increase of activity at the beginning of cycle 21. Solar minimum and the maximum observed brightness of Titan and Neptune both occurred in 1976. (The maximum of cycle 21 is forecast for late 1979 or early 1980, with a sunspot number ∼1503.) We hypothesise that what we have observed are changes in planetary albedos induced by solar activity. Such changes may have an important bearing on the energy balances of the outer planets and their satellites.
Published Version
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