Winifred Sawtell Cameron

EVIDENCE FROM THE MOON'S SURFACE FEATURES FOR THE PRODUCTION OF LUNAR GRANITES

Abstract If tektites come from the moon, they indicate a granitic constitution for a considerable portion of the outer crust, especially if allowance is made for the chemical effects of volatilization (loss of alkalies). The evidence for granitic rocks from the morphology of the moons surface is considered in this paper. The displacement of the center of the moons visible face with respect to the center of mass is considered evidence of the existence of isostasy on the moon. It is shown that this displacement is not merely a limb phenomenon, amd that it is probably not explicable in terms of the kind of lumpy interior proposed by Urey to explain the differences of the moments of inertia. Evidence for characteristic granite landforms, including tholoids and laccoliths, is summarized. The possibility that the maria are produced by the fluidization of volcanic ash is considered. The transporting fluid is considered to be the contained gases as in a terrestrial ash flow. Ash flows on the earth are responsible for the emplacement of a large fraction of all volcanic ash. From a study of the physics of ash flows, it is concluded that the fluidization should be more effective on the moon. It should require only about 1 30 as much gas to transmit a given amount of rock, an amount which is well within reasonable expectations for the gas yield from the rocks. It is concluded that the morphology of the moons surface does not contradict the notion that large amounts of acid rock are present on its surface.

Lunar ring dikes from orbiter I.

Orbiter photographs of the wall of a large circular formation on the moon show that the wall is a convex body resembling a flow of viscous lava. The slopes are less than the angle of repose of dry rock; hence an explanation in terms of mass wastage is hard to support. The viscosity is approximately 1013 centimeter-gram- second units, indicating an acid lava.

Operation Moon Blink and report of observations of lunar transient phenomena.

Abstract A network of optical Moon Blink devices has demonstrated its ability to detect red or blue temporary lunar color phenomena. NASA has organized a supplementary network of observers to confirm the Moon Blink observations and to report all types of transient lunar phenomena to a data collection center at Goddard Space Flight Center. Observations covering 11 2 years of the program are analyzed and discussed in connection with various theories for the cause of these phenomena.

An analysis of the distribution of boulders in the vicinity of small lunar craters

Nine Orbiter 3 high-resolution photographs were examined at three sites for distributions of boulders around craters ⩾ 110 m in diameter; three kinds of distributions were noted. Some had boulders inside and far outside (designatedα), others had boulders only inside or on their ramparts (β), and some had no detectable boulders (γ). Additionally, shapes or morphologies of craters were classified according to their resemblance to one of three Jaffe models (1965); a third classification involved the depth of particulate overlay (Jaffe, 1965). Crater morphologies were classified (A) if they were relatively shallow with sharp, raised rims, (B) if they were rimless and shallow, and (C) if they were relatively deep and had low, broad rims. The data suggested that there were strong relationships between crater types and boulder distributions in which, generally, A-type was related to theα-distribution, B-type toγ-distribution, and C-type toβ-distribution. Plots of numbers of craters of each crater type and each kind of boulder distribution versus steps of overlay for each site and for the totality of craters considered indicated that neither boulder distribution nor crater type represented orderly progression of age or erosional evolution. The apparent overlays for the As and Cs and for theαs andβs were similar, implying similar ages or stages of erosion. It is suggested that they represent two kinds of primary craters and that the Aαs are of impact origin while the Cβs are of volcanic origin. The Bγs probably represent later stages of erosion of the Cs and possibly of some As.

Manifestations and possible sources of lunar transient phenomena /LTP/

Several different manifestations of lunar transient phenomena (LTP) have been reported. These include: (1) brightenings - both sudden and slow, (2) reddish - both bright and dull, (3) bluish -both bright and dull, (4) fairly abrupt dimmings or darkenings, and (5) obscurations, which may be accompanied by any of the other four manifestations. Approximately 200 lunar features exhibiting such anomalies have been reported at least once, but 80% of all observations are found in less than a dozen sites and 60% are found in about one-half dozen sites.An observing program is being conducted for the Association of Lunar and Planetary Observers which is designed to monitor the LTP sites, the seismic epicenter sites and non-LTP comparison sites. It addresses the ‘brightenings’ category of observations and is designed to establish normal brightness of each observed feature for all phases of a lunation. It also seeks to establish a quantified ‘seeing’ scale. About one-half dozen observers have reported albedo measures (estimated from an albedo scale set up by each observer).The most extensive new data on albedo versus age (phase of Moon) are for the crater Dawes. Several LTP effects have been discerned in Dawes.In addition, seeing estimates, based on the behavior of a stars diffraction disk, provided some unexpected results when disk behavior is compared with other subjective estimates of seeing.

Possible lunar ring dikes

Terrestrial ring dike structures are features consisting of one or more series of concentric fracture systems along which the central block often subsided and up through which lavas intruded and extruded and other volcanic features formed.Before the lunar probe satellites, a search for lunar features that showed characteristics of terrestrial ring dikes was conducted using the LAC charts andKuiper Atlas photographs. More recently the search was extended on the nearside features and to the farside features using the Lunar Orbiter series of photographs resulting in a catalog of 559 nearside candidates and 82 farside. Features exhibiting one or more of the following four criteria were included as lunar analogs to terrestrial ring dikes: (1) inner ridge(s) approximately concentric with the crater wall, (2) inner rill(s) approximately concentric with the crater wall, (3) outer ridge(s) and/or rill(s) approximately concentric with the crater wall, and (4) interior and exterior slopes of the crater wall approximately equal (implying extrusion of lava along a ring fracture). Equal slopes are in contradistinction to a central source eruptive feature or an impact feature both of which usually produce craters with walls whose inner slopes are about twice as steep as their outer flanks, which characterize the vast majority of lunar craters.Features exhibiting each of the four criteria were found and some had combinations of two or more including rills merging into ridges, e.g., in Taruntius and Posidonius. Gambart is an example of equal inner and outer slopes, while Hesiodus A and Marth are two of the best examples of complete inner rings concentric with the outer rings. Ten percent of the candidates were probable impact craters but had subsequent volvanic activity of a ring dike nature.The initial search showed a distribution of the possible lunar ring dikes that was non-random and strongly associated with the margins of the maria, further implying that they are volcanic features. This relation was upheld when extended by the recent survey. The anticipated dearth of farside ring dikes was corroborated in our study and their distribution is restricted to those few mare-like areas on the farside, further supporting the volcanic nature of these features

Lunar transient phenomena /LTP/ - Manifestations, site distribution, correlations and possible causes

Abstract The author has been compiling a catalog of LTP reports (temporary changes observed on the moon). More than 1,400 of these observations, of which 1,353 have ancillary data, were analyzed in an attempt to determine the possible causes of LTP. There were 201 sites reported at least once; about 1 2 had two or more reports. One dozen sites contain 70% of all observations, and one site, Aristarchus, provides 30%. Of the dozen most reported sites, 1 2 are rayed and 1 2 are dark flat-floored craters. The distribution of sites strongly favors the borders of both the terra and marial sides of the maria. Many are within the maria, and a very few are inland; yet most of these are associated with dark flat areas. The phenomena manifest themselves in five categories, viz., Brightenings, or Darkenings, or as Gaseous, Reddish and Bluish events. Among the hypotheses proposed for their causes are tidal, low-illumination/thermoluminescence, magnetic-tail and solar-flare effects. Analyses were conducted to see if different phenomena had different causes. There is some suggestion that they do. As concerns the tidal effects. the strongest peaks are at 0.5 (apogee) for Gaseous and Darkenings phenomena, 0.6 for Reddish events, and 0.7 for Brightenings. Reddish LTP have the strongest correlation with sunrise, while Aristarchus, Plato, Ross D area, and Bluish phenomena have the strongest correlations with solar-flare activity that produced magnetic storms on earth. “All” observations, the ones labeled “Best” (probable true anomalies), and Aristarchus, showed minima in the first half and maxima in the last half of the anomalistic (tidal) period. Histograms of several individual sites, including neighboring ones, behave differently, e.g. Aristarchus and Herodotus. When observed data are compared with expected observations (assumed to be evenly distributed) there were various correlations. For the Best data, 12 and 10% of the LTP fall close to perigee and apogee, respectively, and 10% would be expected for each. Seventeen percent occur within one day after sunrise when 3% would be expected; 20% occur while the moon is in the earths magnetopause where 14% would be expected, and 12% occurred the same day the earth had a magnetic storm where 3% would be expected. Charts of albedo vs. age of several points for ten features were constructed. From these the normal behavior of the features throughout a lunation period was obtained. Measures that depart 2 or more full steps in Elgers albedo scale, are considered to be anomalies. Several cases of anomalous measures show up; e.g., for points on the south wall of Eimmart an albedo of 3.5 was reported once at age 10 days while for age 9 days the average albedo was 8, as it was afterward at age 11 days. The 3.5 may have been an anomalous darkening but unnoticed by the observer. Most of the features remained stable. A few exceptions were found, with Dawes showing the most anomalies. These amounted to 12% by nights or 2% by individual measures. Thus, monitoring the moon may yield an LTP once in ten nights, or 50 observations. All hypotheses show correlations with some categories and some features. Sunrise correlation is the most frequent correlation. Few correlations involve as many as 50% of the observations. The distribution of all LTP sites is different from and unique compared with deep- and shallow-focus moonquake epicenters. Routine albedo measures reveal unobserved variations which amount to about 10% in nights of observation bu 2% of individual albedo measures.

Tektites - volcanic ejecta from the moon?

The problem of the origin of the enigmatic tektites is still unsolved. The two leading hypotheses - viz., ejecta from terrestrial impacts, and ejecta from lunar volcanoes or lunar impacts, each encounters serious difficulties. The former has ballistic and water content difficulties, while the latter has some compositional difficulties, especially in the trace elements, as determined from the returned samples. It is possible that the latter problem may be met through lunar volcanic ejecta from sites suggesting more differentiation than the majority of the Moon. That such features may exist is suggested from the identity of some granitic material in the returned rocks and soil samples implying fairly sizable source regions on the Moon.The rare terrestrial strewn tektite fields require restrictive ballistic trajectories from the Moon. Calculations reveal that ellipses of varying, decreasing sizes which depend on velocity of vertical ejection from which ejecta will intersect the earth at low-entrance angles occur on the nearside of the Moon. Reasonable velocities were chosen (2.55 to 3.0 km s−1) and these ellipses circumscribe areas with longitudes between 30 and 50° east and latitudes between 7° north and south of the Moons equator. These areas were searched for evidence of volcanism. As tektites have compositions ranging from acidic (major tektites) to basic (micro-tektites) contents of silica (SiO2) both acidic and basic volcanic features were sought.Since tektites range in age from about 30 million to 700000 yr old, they imply recent volcanism. Lunar Transient Phenomena (LTP) and data from various Apollo missions indicate that mild internal activity may still be occurring on the Moon. LTP sites are logical sources to investigate, of which four occur within the above delimited regions. These and their surroundings were examined and a number of possible explosive volcanism sites were found. These sites are identified and discussed after a review of the manifestations found from the various kinds of terrestrial volcanism for which lunar counterparts were sought.