Cover Page/Proposal Summary

ROSS-00    NRA 00-OSS-01

Date Due: 4/28/2000

The planet Mercury is subject to the same space-weather related phenomena that occur at Earth - but on a much shorter timescale since the spatial scales involved are smaller, the magnetic field is weaker, and the solar wind flux is approximately an order of magnitude larger. While the analogy is imperfect, there is great advantage to study of a system which is far enough away that the entire atmosphere can be imaged at once, and which responds to changes in the interplanetary environment on timescales of a few minutes. We have already shown that the exosphere responds to changes in the magnetosphere in response to the changing solar wind pressure and the IMF. The details of this interaction are still relatively uncertain. However, in addition to the alkali species, we now have observations of an additional species, Ca, which appears to be promoted into the atmosphere by ion sputtering. This hypothesis is controversial, and rightly so, since our data set is limited. We will pose and answer the following specific questions 1) how does the solar cycle affect the exosphere of Mercury, 2) and what does this tell us about the relative roles of meteoritic vaporization, photon-stimulated desorption and ion sputtering as source processes? Can observations of Mercury's exosphere at eastern elongation be used statistically to predict space weather at Earth approximately six days later? We will reduce and publish 13 years of observations of the Hermean atmosphere, compute the column abundance, model the source rates for the three proposed source processes, and compare observations with predictions of the model. Our colleagues at UCSD will provide solar wind density and speed at Mercury. Our colleagues at Rice University will provide us with magnetosphere models required to accurately model the ion sputter source for the atmosphere of Mercury.

Certification of Compliance with Applicable Executive Orders and U.S. Code

By submitting the proposal identified in this Cover Sheet/Proposal Summary in response to this NRA or AO, the Authorizing Official of the proposing institution (or the individual proposer if there is no proposing institution) as identified below: