EDITOR'S NOTE: Professor Theodore E. Madey, director of the Laboratoryfor Surface Modification (LSM), can be reached for interviews at (732)445-5185, or via email at firstname.lastname@example.org. Additionalinformation on LSM can be obtained at http://www.physics.rutgers.edu/lsm/.
NEW BRUNSWICK/PISCATAWAY, N.J. -- Two Rutgers physicists have performedthe first laboratory studies to identify processes that replenish theMoon's thin atmosphere.
Research Associate Boris Yakshinskiy of Highland Park and ProfessorTheodore E. Madey of Bound Brook, both of Rutgers' Laboratory forSurface Modification, the department of physics and astronomy of theFaculty of Arts and Sciences-New Brunswick, announce their findings inthe Aug. 12 issue of the journal Nature. They describe the creation oflaboratory simulations of the lunar surface and then demonstrate how theresupply of sodium to the lunar atmosphere from the surface occurs.
The relatively thin atmosphere of the Moon, as well as that of theplanet Mercury, has been shown to contain measurable amounts of atomicsodium and potassium vapor. Because these atoms remain in theatmosphere for only a few hours, they must constantly be resupplied. The Rutgers physicists undertook experiments to uncover the mechanismsrequired for the continuing presence of one of these elements (sodium)in the atmosphere, as observed over time by other scientists.
"Several mechanisms have been proposed to explain the resupply ofatmospheric components from the lunar surface," said Madey. "Otherscientists have considered the effects of the solar wind (a looselypacked stream of particle radiation from the sun), micrometeoriteimpacts, release of elements caused by surface heating, and releasestimulated by the effects of light, but there is little data to supportany one explanation and no general agreement about which processes arethe most important."
"We simply place a sample of the surface we intend to investigate in agood vacuum, we start throwing photons, electrons, and ions at it, andthen we look at what comes back from the surface and how," saidYakshinskiy, describing the use of highly sophisticatedultra-high vacuum apparatus, X-ray photoelectron spectroscopy,photon-stimulated desorption, temperature programmed desorption andlow-energy ion scattering in laboratory analysis.
As silicon-dioxide (SiO2) is the major component of the Moon's surface,SiO2 films were prepared in vacuum to simulate it and then sodium wasdeposited upon the films. The simulated lunar surfaces were bombardedwith the photons, electrons and ions to test the effects of light, heat,meteoritic and other radiation mechanisms. Measurements of theliberated sodium were taken and analyzed.
Based on their experimental results, Yakshinskiy and Madey conclude thatthe electron flux or flow from the solar wind is too small to expelsodium from the lunar surface, "...but the solar photon flux (the lightitself) is more than sufficient. These measurements provide strongscientific support and rationale for the arguments ... that aphoton-stimulated desorption (replenishment) process plays a major rolein production of the lunar sodium atmosphere."
Some observable short-term, local sodium concentrations may also beattributed, they believe, to associated meteor showers. With respect tothe planet Mercury, they believe that heat contributes to the surfacerelease of sodium, given the high daytime temperatures, but the photonflux is still likely to play a major role, as on the Moon.
"As we move out beyond the confines of our home planet, we must look tonew scientific approaches to deal with the questions posed in this newera of planetary exploration," said Madey. "The study of surfacemodification is one such approach, already providing some of the answerswe seek and helping us to understand the environments we will encounteron our solar system neighbors."
The Laboratory for Surface Modification provides a focus for researchinto atomic-level phenomena that occur on the surface of solids. Itinvolves the overlapping disciplines of physics, chemistry, materialsscience and engineering with applications to semiconductor devices andcatalysis, as well as surface processes in outer space.
Yakshinskiy and Madey's paper in Nature is titled "Photon-stimulatedDesorption as a Substantial Source of Sodium in the Lunar Atmosphere." Journalists can view the paper prior to publication at http://press.nature.com/.
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