Velocity Structure in Mercury's Exosphere
R.M. Killen (Southwest Research Institute), A.E. Potter (Lunar and Planetary Institute), T.H. Morgan (Southwest Research Institute)
A high resolution line profile of the Na D2 emission from Mercury was
obtained on May 29, 1997, at the McDonald Observatory 107" telescope
with the echelle spectrograph in double pass (Potter and Morgan 1997,
BAAS, in press). This line profile indicates that the bulk of the
atmosphere is hot, in agreement with evidence from the image data which
indicates a gas at approximately 6000 K (Potter and Morgan 1997 Adv.
Space Res.in press). A line profile measured in 1986 (Potter and
Morgan 1987, Icarus 71, 472) indicated that the bulk of the sodium was
cooler, <1100 K, indicative of possible temporal or spatial variation.
Previous estimates if the gas temperature were based on a Chamberlain
exosphere model, assuming optically thin conditions. We have used a
Monte Carlo radiative transfer program to investigate the velocity
distribution in the exosphere. Models will be presented for line
profiles simulated for various source processes and will be compared
with the line profile and image data.