The following is a condensation of remarks by J. Hedley Robinson in the
December 1986 issue of the British Astronomical Association. As publish in Sky
& Telescope March 1991, in Lunar Transient Phenomena by Winifred S.
Cameron.
1. Tidal: Tidal stress is greatest when the Moon is at perigee. The
tidal pull may release strains in the Lunar crust and permit the release of
trapped gases. The Earth's tidal effects on the Moon is 32.5 times greater that
the Moon's effect on the Earth.
2. Albedo Changes: Albedo changes due to dust movement. There is
essentially no atmosphere on the Moon to raise dust, so this does not seem
likely as an explanation. (This opinion has since change due to recent missions
such as Clementine and Lunar Prospector, see conclusion)
3. Thermal Shock: The Lunar surface varies from 125 degrees to -80
Celsius during a two hour period at both sunrise and sunset, and most L.T.P.'s
occur within three days of the local sunrise. L.T.P.'s could be related to the fact
that dissimilar materials expand and contract at different rates. Although the
Maria heat more rapidly than other parts of the Moon's surface, at a depth of
just 10 cm the rock temperature is constant. Thermal conditions may be regarded
as incidental to L.T.P.'s rather than the main cause.
4. Magnetic: Solar plasma bombards the Lunar surface, even when the
Moon is in the Earth magnetic tail, and the movement of the Moon in and out of
the magnetic tail changes the field strength. But charge particles penetrate the
Lunar surface to only one-third the depth reached by the Sun; thermal rays. If
thermal shock is considered to be insufficient to cause L.T.P phenomena, then much
weaker electromagnetic effect below the surface must also be discounted.
5. Ultraviolet: Ultraviolet radiation from the sun might cause
fluorescence at visible wavelengths, because there is virtually no atmosphere to
shield the Lunar surface. I doubt that the effects is strong enough to produce
visible reactions as bright, or large, as the usual L.T.P.'s.
6. Solar Wind: Solar-wind plasma impacting the surface could produce
an electric discharge, but I doubt that the energy involved is great enough to
cause an effect visible from Earth. L.T.P.'s could, however, be caused by the
explosion of chemically reactive molecules and free radicals in small hollows;
and the solar wind plasma may produce such reactive molecules in rocks. But
solar-wind plasma hardly looks like a prime cause.
7. Spectral Diffraction: Spectral diffraction from surface grains or
irregularities too small for telescopes resolution may cause color. The Lunar
surface present many angles to the observer, and these vary with liberation With
the varying Lunar surface slopes, many simultaneous diffraction angles should be
presented. But if this were the cause of the L.T.P.'s the effects should show all
over the disk from time to time, whereas they in fact show local preferences.
8. Meteor Strikes: These have been claimed frequently. One of the best
observed was reported by the Smithsonian Institution near the Apollo 14 site on
May 13, 1972, when a meteor impact release an energy equal to that of 1,000 tons
of TNT. But meteor strikes cover a small area of the Lunar surface when compared
to the size of the L.T.P.'s.
9. Moon Quakes: Moon quakes are often deep seated but very week, with
preference for times of perigee or apogee. There seems to be no obvious
connection between the frequency of moonquakes and sighting of L.T.P phenomena.
10. False Color: False color is a regular feature in larger telescopes
due to terrestrial atmospheric conditions. This can be guarded against by
comparing a suspected L.T.P event with the appearance of other formation on the
Lunar surface at the same time, and is well recognized by practiced observers.
11. Piezoelectric Effects: The piezoelectric effect is well known on
Earth, for example when rock strain generates a strong electric field that
ionizes the air above the rock, causing a glow. The field moves with the strain
source. There are soviet reports that the magnetic fields drops suddenly when
underground tension is released.
Conclusion: The foregoing indicates the many different ideas have been
proposed as possible mechanisms for L.T.P. As you can see the author J. Hedley
Robinson could not give any one cause any more weight than the other. This is a
great dilemma and why many scientist do not consider L.T.P to be a real phenomena,
since no satisfactory mechanism has been found that could account for the large
energy output of many L.T.P events. But with the conclusion of the Clementine and
Lunar Prospector mission and the in-depth examination of the Apollo and Surveyor
data new ideas have been presented that give fresh insight on a possible
mechanism for this phenomena.
The Lunar Sourcebook a user's guide to the Moon. That was published in
1991 states information about dust levitation that would account for the many
different kinds of L.T.P events documented over the years. This one phenomena
could explain seven classifications of L.T.P events such as darkening, bluish,
reddish, obscurations, false dawn, shadow effects, and contrast effects. This
information is presented in chapter 9.2.3 "Electrostatic Charging and Dust
Migration": "A large number of observations of lunar transient events,
especially unexplained glows and obscurations, have been noted over two
centuries of ground based observations, continuing up to the present (Cameron,
1974, 1978; see section 11.4.2)These changes in lunar brightness may rise times
of <1 sec to 5 sec and range in color from reddish to bluish."
"More recent reports of such phenomena include observations by the
Apollo astronauts (McCoy and Criswell, 1974a; McCoy, 1976a,b). Although these
observations have never been satisfactorily explained (for discussions, See
Cameron, 1974, 1978 and section 11.4.2), electrical phenomena in the lunar
surface layers are one possible mechanism."
"The large electrical conductivity change with visible and UV
irradiation (discussed above). combined with the very low electrical
conductivity and dielectric losses of lunar materials, can produce an extremely
efficient electrostatic charging mechanism between opposite sides of lunar
terminator. Across this moving boundary, charging of lunar soil particles could
be sufficient to levitate them above the surface, producing a "dust
storm" of particles that would follow the solar terminator around the Moon.
McDonnell and Flavill (1977) and McDonnell (1979)have calculated that such
electrostatic levitation would extend to 10 meters above the lunar surface.
However if dust could reach higher altitudes, such a phenomenon could explain
some observations of the Apollo astronauts, who reported and drew pictures of
"streamers" and bands of corona/zodiacal light (the results of light
scattering by dust?) extending several kilometers above the lunar surface while
approaching orbital sunrise (McCoy, 1976a,b)."
See Documented Moon Glows: Zodiacal
Lights & Solar Corona
"The Apollo 17 Lunar Ejecta and Meteorites (LEAM) experiment (Berg et
al., 1973) found increased particle counts during the passage of the terminator
over the instrument (Berg et al., 1974)and the experimenters noted that
"...all of the events recorded by the sensors during the terminator passage
are essentially surface micro particles carrying a high electrostatic
charge." Other experimenters observed that "the particles event rate
increases whenever the terminator passes over the instrument. This increase
starts some 40 hours before sunrise and ends 30 hours after it" (Rhee et
al., 1977). Such charged, levitating soil particles, moving across the lunar
surface, could create visibility problems during passage through the terminator,
and the particles would also readily adhere to surfaces, creating
coatings...Another hypothesis to explain lunar transient phenomena is that they
are associated with electrodynamics effects generated during rock
fracturing" (Zito, 1989).
More information about possible causes for L.T.P are presented in chapter
11.4.2 "Lunar Surface Processes and Evolutions" in the Lunar
Sourcebook a user's guide to the Moon. "What causes the lunar transient
events?" These "transient events include enigmatic brightening or
obscurations observed by Earth astronomers, mostly from the Aristarchus Plateau
but also associated with a large number of widely scattered impact craters
(Tycho, Gassendi, Humbolt, and many others; see Middlehurst, 1977). these events
are mentioned briefly in section 9.2.3, where electrostatic charging of lunar
surface dust is suggested as one possible cause of the optical effects. It is
also possible that these events are related to gas emissions from the lunar
interior, perhaps enhanced in area of high KREEP content (where gases may form
over long time spans by radioactive decay of nongaseous elements), at sites where
relatively large but young impact craters have fractured the outer crust, and at
sites associated with extensive fracturing and rilles formation along mare basin
rims (see Fig 4.29c)."
It been reported as well that the Surveyor spacecraft detected horizon glow
phenomena as reported in Sky and Telescope magazine in the September 1973
issue page 146. "A patchy glows has been discovered on the Moon's horizon at dusk that is believed to be caused by individual dust clouds being
continually formed above the hills, crater rims, and rocks which remain sunlit
while the shadow of night advances over the lower surroundings. J.J. Rennilson
(California Institute of Technology) and D.R. Criswell (Lunar Sciences
Institute, Houston) point out that glow was originally reported by Surveyors 5,
6, and 7, and possibly also Surveyor 1, between 1966 and 1968. The Russian lunar
rover Lunokhod 2 probably detected the glow in early 1973."
See Documented horizon glows by Surveyor: Horizon
Glows
The Clementine spacecraft also detected the glow on the horizon or limb of
the Moon as reported in Science News 1994, page 145:197, by R. Cowen.
"The spacecraft Clementine, now engaged in surveying the Moon from orbit,
has apparently recorded once again a perplexing sky glow that precedes lunar
sunrise and follows lunar sunset." Clementine Limb
Shots. The second page of Clementine shots shows the faint nebulous clouds
along the horizon. These shots are not washed out by the intense brightness of
the Solar Corona. See Nebulous Clouds.
I have personally observed a number of L.T.P over the last twenty years that
seem to indicate a gaseous medium or dust levitation taking place. This has been
observed by myself inside the crater Aristarchus on several occasions. I have
also observed an intense darkening event over the crater Reiner and inside the
crater Proclus. This may indicate that a significant dust levitation is taking
place on the crater floor or out gassing that disturbing the dust. The most
recent darkening event was observed by two other observers and myself over the
crater Picard during the Clementine observing program. I have also documented on
several occasions the nebulous appearance of the central peak of the crater
Tycho and possible dust levitation inside the shadowed filled region of Tycho.
The mountain peak Piton has also been observed to have strange appearance such
being shrouded in a cloud or gaseous medium.
The phenomena has been witness by many others and not just by myself, to
experience it first hand is much different than reading about it in a book. When
your turn comes to witness such an event, you will understand the force that
motivates me to continue to watch are nearest neighbor as often as I do.
David O. Darling