Sodium and potassium atmospheres of Mercury

Same-day images of the sodium and potassium atmospheres of Mercury were collected over a five-day period from December 6 to 10, 1990. Both sodium and potassium emissions were more intense at ''high latitudes and varied from day to day. The maximum emissions for sodium and potassium were strongly correlated with one another. These results support the view that sodium and potassium are both generated by the same process, namely sputtering of the surface at high latitudes by magnetospheric particles. The atmospheric abundance of potassium relative to sodium was less than previously observed. It is suggested that this resulted from more rapid removal of potassium from the atmosphere by photoionization during periods of high solar activity. Published by Elsevier Science Ltd.