Neutral solar wind generated by lunar exospheric dust at the terminator

Abstract

[1] We calculate the flux of neutral solar wind observed on the lunar surface at the terminator due to solar wind protons penetrating exospheric dust grains with (1) radii greater than 0.1 mm and (2) radii greater than 0.01 mm. For grains with radii larger than 0.1 mm, the ratio of the neutral solar wind flux produced by exospheric dust to the incident ionized solar wind flux is estimated to be $10 À4 -10 À3 for solar wind speeds in excess of 800 km s À1 but much lower (<10 À5 ) at average to slow solar wind speeds. However, when the smaller grain sizes are considered, this ratio is estimated to be !10 À5 at all speeds and at speeds in excess of 700 km s À1 reaches $10 À3 . These neutral solar wind fluxes are easily measurable with current low-energy neutral atom instrumentation. Observations of neutral solar wind from the surface of the Moon would provide independent information on the distribution of very small dust grains in the lunar exosphere that would complement and constrain optical measurements at ultraviolet and visible wavelengths.Citation: Collier, M. R., and T. J. Stubbs (2009), Neutral solar wind generated by lunar exospheric dust at the terminator, J. Geophys.

Lunar surface electric potential changes associated with traversals through the Earth's foreshock

“…1977;Criswell and De, 1977;Borisov and MaU, 2006;Wang et at. 2007) with observable and potentially observable consequences tad Criswell, 1974;McCoy, 1976;Collier and Stubbs, 2009;stubhs.t 01" 2010).…”

Exospheres and Energetic Neutral Atoms of Mars, Venus and Titan

“…While its density is extremely low, owing to the long flight distance over the lunar terminator region, a detectable ENA flux originating from the charge exchange with the solar wind is predicted (Futaana et al 2008a). Dust in the exosphere may also produce an ENA flux of the solar wind origin (Collier and Stubbs 2009). On the other hand, Mars, Venus, and some comets (particularly when they are close to the Sun) have sufficiently dense atmospheres to form strong ionospheres, while lacking an intrinsic magnetic field.…”

On lunar exospheric column densities and solar wind access beyond the terminator from ROSAT soft X-ray observations of solar wind charge exchange

“…With some assumptions, we can use the observed limb‐brightening soft X‐ray flux to estimate the associated lunar exospheric surface density. In an approach similar to that of Collier and Stubbs [], we assume we are viewing the Moon from the side and take a to be the radius of the Moon, 1738 km. We wish to evaluate the column density, C , where l is the distance along the line of sight measured from the tangent point.…”