FINE DUST IN THE LUNAR ENVIRONMENT

The Third Moscow Solar System Symposium

V.V. Shevchenko, A.A. Berezhnoy, E.A. KozlovaSternberg Astronomical Institute, Moscow State University

Space Research InstituteMoscow, RussiaOctober 8-12, 2012

Surveyor’s Images of Horizon Glow

Surveyors 5, 6, and 7 captured the first evidence of dust transport on airless bodies with their television cameras.View of horizon approximately 15 minutes after

local sunset (Courtesy NASA/JPL).

Surveyor’s Images of Horizon Glow

Just after sunset, a horizon glow was observed above the western horizon. This was interpreted to be forward scattered light from a cloud

of dust particles with radii ~5 μm, vertical dimension ~3-30 cm, and horizontal dimension ~14 m.

View of illumination along horizon approximately 90 minutes after local sunset (Courtesy NASA/JPL).

Image of Surveyor 6 casting an 18-meter-long shadow with the sun just 8 degrees above the horizon. LROC NAC image M117501284L.

Credit: NASA/Goddard/Arizona State University

western horizon

Surveyor’s Images of Horizon Glow

The image was taken by the Surveyor 6 on November 24, 1967, one hour after sunset.

Modeling Dust Clouds on the Moon

POSITION OF THE SOLAR DISK

western horizon

Surveyor’s images of horizon glow

These observations were interpreted to be forward scattered light from a cloud of dust particles with radii ~ 5 µm, vertical dimension ~ 3-30 cm, and horizontal dimension ~14 m, , and

about 50 grains on cm–2 (Szalay and Horanyi, 2012).

The very small size of particles is an important condition of existence of a horizontal levitation of a lunar dust.

In the morning, the storm raging on the Moon Apollo 17, 1972

This is evidenced by the results of the data obtained with the instrument LEAM (Lunar Ejecta and Meteorites).Credit: NASA

This is a sketch of the lunar sunrise seen from orbit by Apollo 17 astronaut Eugene Cernan. On the right, the sketch is highlighted to show the sources of the scattered light: red indicates Coronal

and Zodiacal Glow, blue is the Lunar Horizon Glow, perhaps caused by exospheric dust, and green indicates possible "streamers" of

light (crepuscular rays) formed by shadowing and scattered light. Credit: NASA

ORBITAL OBSERVATIONS

This is a picture of coronal and zodiacal light (CZL) taken with the Clementine spacecraft (1994), when the Sun was behind

the Moon. The white area on the edge of the Moon is the CZL, and the bright dot at the top is the planet Venus. Credit: NASA

ORBITAL OBSERVATIONS

Rocks not coated with dust.Laser reflectors continue to operate 35 years later.

So, it’s needed to find the origin of very fine (~ 5 m) dust particles

in lunar environment.

BUT:

POSSIBLE ORIGIN OF THE FINE DUST

IN LUNAR EXOSPHERE

The Third Moscow Solar System Symposium

V.V. Shevchenko Sternberg Astronomical Institute, Moscow State University

Space Research InstituteMoscow, RussiaOctober 8-12, 2012

. There is no official definition of what size fraction constitutes "dust", some place the cutoff at less than 50 - 70 micrometres in diameter.

Regolith Particle Size-Frequency Distribution

Reiner Carrel Daniell Maury A

M109569228L

M111422761L M106676014R M108964159R

SLOPE AVALANCHE DEPOSITS IN CRATERS

LRO/LROC IMAGES

SLOPE AVALANCHE DEPOSITS IN CRATER MAURY

Fine fraction (~ 5 m) seems to have played a major role in the creation of a high degree of fluidity of sloping

flows.

The area of “failure” in the northeastern wall of crater Diophantus is located at a depth of 290 to 640 m.

Area of “failure” is source of very fine (~ 5 m) dust particles in lunar environment

Electrically charged grains could be levitated into the cloud by intense electrostatic fields (> 500 V cm–1) extending across the sunlight/shadow boundaries.

Detailed analysis of the HG absolute luminance, temporal decay, and morphology confirm the cloud

model. The levitation mechanism must eject 107 more particles per unit time into the cloud than could micro

meteorites. Electrostatic transport is probably the dominant local transport mechanism of lunar surface

fines (Rennilson and Criswell, 1973) .

Levitation mechanism

One of unsolved problems of sloping movement of substance is to understand the causes for the existence of the fine faction

of regolith at a depth of hundreds of meters

KAGUYA SUBSURFACE DATA

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