1. SWCX and the production of X-rays SWCX produces X-rays when heavy ions in the solar wind interact with neutrals in the Earth’s exosphere, cometary nebulae, planetary atmospheres, interstellar neutrals and at the heliospheric boundary by a process such as: O q+ + H → O q+* + H + If the ionisation state q is sufficiently large, the ion de-excites, emitting a soft X ray photon. The SWCX can tell us about the constituents and speed of the solar wind. The number of heavy ions in the solar wind is related to activity on the Sun, for example to the frequency of Coronal Mass Ejections. The spectrum below, taken from an observation with XMM-Newton of the Hubble Deep Field North, clearly shows ions from solar wind C, O, Fe, Ne and Mg [3]. The X-ray satellite ROSAT found a correlation between solar activity and enhancements in the soft X-ray background. o1 University of Leicester, email:jac48@star.le.ac.uk The Advantages of a Lunar Site A lunar observatory would provide an ideal location for viewing the SWCX emission from the magnetosheath. Situated as such it would provide an overall, dynamic picture of the Earth-solar wind boundary as it scans the region for a large fraction of each terrestrial month. The observing conditions and viewing angles from the Moon are unlike those of current X-ray telescopes, such as XMM-Newton, which spend a large fraction of their orbit within the magnetosphere. SWCX emission can also be studied from interactions occurring in the tenuous lunar atmosphere, which is formed by sputtering processes and out-gassing of trapped volatiles. The Moon is not protected by a magnetic field and so solar wind particles reach right up to the lunar surface References [1] Sembay S., Carter J. A., Collier M. R., Snowden S. & Fraser G. (2007) [2] Robertson I.P. and Cravens T.E., Journal of Geophys.l Res Letters, Vol 30., 8, 1439, 2003 [3] Snowden, S., Collier M.R. and Kuntz K., 2001, ApJ, 610, 1182-1190, 2004 [4] http://www.star.le.ac.uk/xra/facilities.shtml Telescope Design The telescope would consist a spherically slumped micro-channel plate optic, similar to the proposals for LOBSTER [4]. Microchannel plates are both lightweight and compact. The exact specifications have yet to be constrained, depending on the limits of the science goals, however, the field of view of this optic would be designed for viewing of the SWCX. The telescope’s grasp (field of view times effective area) depend on the focal length and diameter of optic (see the panel before right for an iridium coated optic). Preliminary plans for the total mass of the instrument would be under 40 kg and require 20-30 W in power, depending whether the instrument requires an independent power source, or is combined with that of another project. The telescope is envisaged as a low-cost, low-mass addition to some larger lunar science package. J. A. Carter 1, S. F. Sembay 1, G. Fraser 1, M. Lester 1, M. R. Collier 2, S. Snowden 2. There is a renewed international interest in the Moon as a focus for scientific and technical exploration over the next few decades. We present a proposal for low-mass X-ray telescope that could make an important scientific contribution to a lunar exploration programme at relatively low cost [1]. The primary science goal of the telescope would be to study soft X-ray emission from the Solar Wind Charge Exchange (SWCX) process that occurs between the solar wind and both the tenuous lunar atmosphere and geocoronal neutrals which are concentrated in the Earth magnetosheath. In particular, observations of the latter could provide a unique 3- dimensional view of the dynamic interaction of the solar wind and the Earth's magnetic field. An X-Ray Observatory for studying Solar Wind Charge Exchange X-ray emission Left – SWCX ions. Above, X rays with solar activity Primary Science Goal Although models describing the SWCX X-ray emission around the Earth have been produced, (Figure below; [2]), this theoretical work has yet to be backed up by dedicated observations which can constrain the details of the model and extend our knowledge of the solar wind. Particular areas of interest would include studying the ion concentrations through their spectral signature and mapping the dynamic boundary where energy and momentum are transferred from the solar wind to the terrestrial magnetic field. An X-ray telescope dedicated to studying the SWCX emission from this dynamical region can provide a unique wide area view in contrast to single point in-situ measurements of particle and magnetic densities common to current solar system “space weather” detectors. 2 NASA/GSFC, Maryland, US