Mapping sodium distribution on the surface of Mercury


The distribution of sodium emission over the surface of Mercury is non- uniform, and changes over time. These non-uniformities and time- dependent changes give clues to the processes that produce sodium. Photon-stimulated desorption may be the major sodium source process on Mercury, so the sodium density might be expected to maximize at the subsolar point. Another source process may be sputtering by solar particles that impact the surface at high latitudes in the polar cusps, producing sodium emissions at these locations. Variations in the geographic distribution of sodium-rich minerals might produce localized emissions that do not change position with time. Mapping the sodium emission is a difficult observational problem, since Mercury is seen either against the bright daytime sky, or against a dark sky at very high air masses. We have adapted an image stabilizer utilizing a piezoelectric driven tip-tilt correction mirror for daytime spectral imaging of Mercury. The image stabilizer was originally developed for solar observations at the McMath-Pierce solar telescope. Use of image stabilization results in a noticeable improvement in spatial resolution of our Mercury sodium images. A series of sodium images taken over an eight-day period show changes in which an emission peak in high southern latitudes disappears, and is replaced by an emission peak at high northern latitudes. Further systematic observations and improvements are planned for the image stabilizer system, as well as experimental observations with a low-order adaptive optics system incorporating a commercially available 37-actuator deformable mirror.

35th COSPAR Scientific Assembly