A NASA-funded research team, led by Mihaly Horanyi at the University of Colorado-Boulder (CU-Bolder), has conducted laboratory experiments to bring closure to a long-standing issue of electrostatic dust transport, explaining a variety of unusual phenomena on the surfaces of airless planetary bodies, including observations from the Apollo era to the recent Rosetta comet mission. The research being done at the Institute for Modeling Plasma, Atmospheres and Cosmic Dust (IMPACT) was recently published in the journal of Geophysical Research Letters, and explains how dust may be transporting across vast regions above the lunar surface and rings of Saturn, without winds or flowing water.

High-altitude ray-pattern streamers above the lunar surface reported by the Apollo astronauts, the intermittently appearing radial spokes first seen by the Voyagers over the rings of Saturn, and the fine dust deposits, or “dust ponds” in craters on Eros are all the examples of dust transporting across vast regions without winds or flowing water. Electrostatic dust processes have been hypothesized to explain these space observations. However, no theories until now were able to support these explanations.

The team recorded micron-sized dust particles jumping several centimeters high under ultraviolet (UV) radiation or exposure to plasmas. On the Moon, these dust particles would have been lofted more than 10 cm above the lunar surface, leading researchers to conclude that the Moon’s “horizon glow,” seen in images taken by Surveyor 5, 6, and 7 five decades ago, may have been caused in part by sunlight scattering in a cloud of electrostatically lofted dust particles.

One of the key science findings is that the emission and re-absorption of photo/secondary electrons at the walls of micro-cavities formed between neighboring dust particles can generate unexpectedly large charges and intense particle-particle repulsive forces, which can mobilize and lift dust particles off the ground. “This new ‘patched charge model’ resolved the fundamental mechanisms of dust charging and transport, which have been puzzling scientists for decades,” said Dr. Xu Wang, the paper’s first author.

Top: lunar horizon glow seen in Surveyor 7 image may have been caused by sunlight scattering in a cloud of electrostatically lofted dust particles. Image Credit: NASA.
Middle: laboratory observations of electrostatically lofted dust particles and smoothened surface as a consequence of dust mobilization.
Bottom: micron-sized dust particles jump up to several centimeters high when exposed to plasmas in laboratory. Credit: Wang et al/ U.C. Boulder/LASP

“We expect dust particles to mobilize and transport electrostatically over the entire lunar surface, as well as the surface of any other airless planetary body,” said Dr. Xu Wang. “If so, electrostatic dust activity may be also responsible for the degradation of retroreflectors on the lunar surface.”

In addition to single-sized dust particles, lofted large aggregates showed that electrostatic processes may be responsible for the Rosetta detection of fluffy dust particles released from the surface of Comet 67P.

The laboratory observations also showed dusty surfaces becoming smooth as a consequence of dust mobilization. These electrostatic dust processes could help to explain the formation of the “dust ponds” on asteroid Eros and comet 67P, and the unexpectedly smooth surface on Saturn’s icy satellite Atlas.

To read more about the research being done at the Institute for Modeling Plasma, Atmospheres and Cosmic Dust (IMPACT) visit: http://impact.colorado.edu

Posted by: Soderman/SSERVI Staff
Source: SSERVI IMPACT team

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