Crater Aristarchus Research Articles

Clementine Observations of the Aristarchus Region of the Moon

Multispectral and topographic data acquired by the Clementine spacecraft provide information on the composition and geologic history of the Aristarchus region of the moon. Altimetry profiles show the Aristarchus plateau dipping about 1 degrees to the north-northwest and rising about 2 kilometers above the surrounding lavas of Oceanus Procellarum to the south. Dark, reddish pyroclastic glass covers the plateau to average depths of 10 to 30 meters, as determined from the estimated excavation depths of 100- to 1000-meter-diameter craters that have exposed materials below the pyroclastics. These craters and the walls of sinuous rilles also show that mare basalts underlie the pyroclastics across much of the plateau. Near-infrared images of Aristarchus crater reveal olivine-rich materials and two kilometer-sized outcrops of anorthosite in the central peaks. The anorthosite could be either a derivative of local magnesium-suite magmatism or a remnant of the ferroan anorthosite crust that formed over the primordial magma ocean.

A compositional study of the Aristarchus Region of the Moon using near‐infrared reflectance spectroscopy

Newly obtained near‐infrared reflectance spectra for features on or near the Aristarchus Plateau demonstrate the diversity of compositions in the region. Highland units are of three probable compositions: a feldspar and clinopyroxene assemblage; a probable clinopyroxene, olivine, and possibly feldspar assemblage; and an assemblage composed of olivine or olivine and feldspar. The feldspar‐clinopyroxene assemblage is tentatively correlated with the major Th anomaly centered on Aristarchus crater. The regional pyroclastic deposits on the plateau are composed of greater than 90% Fe2+‐bearing glass. The Aristarchus cratering event fully penetrated any mare or pyroclastics in the target. Evidence for mare‐related material is found in the ejecta on the mare side of the mare‐plateau contact.

The Aristarchus impact event and the effects of target material

AbstractThe relatively well preserved, 42 km diameter lunar impact crater Aristarchus was excavated across the boundary between the Aristarchus Plateau and the mare plains. Previous geological mapping of the different ejecta facies associated with Aristarchus has shown that there are distinct morphological differences between ejecta emplaced on either side of the fault scarp that separates the plateau from the mare. One explanation of this observation is that ejecta behaved in different ways on emplacement depending on the original lithology of the excavated material. To test this proposal, we examine the pre-Aristarchus regional stratigraphy and identify the spectral signatures of each of the material's units. By comparing these data with analysis of the geology and spectral characteristics of the ejecta units, we are able to show the provenance of each of the mappable ejecta facies. The conclusions are consistent with the concept of the crater ejecta asymmetry being related to bedrock characteristics. Using geological mapping, spectral interpretation and present understanding of the impact cratering process, we reconstruct the impact event and suggest how such techniques could be used further to interpret the Moon's composition and history.

Moon: Near‐infrared spectral reflectance, A first good look

A positive identification of the minerals olivine, plagioclase, and several types of pyroxenes were made at several locations on the lunar surface by using remote measurements. For example, the crater Aristarchus is found to have an average pyroxene composition of augite, and plagioclase is obviously present. A dark mantle deposit in the crater J. Herschel is at least partly composed of a mixture of 70% olivine and 30% pyroxene. These determinations were possible because the reflectance spectra for 10–20 km diameter lunar areas have been measured for the first time in the IR spectral region (0.65–2.5 μm) with sufficient spectral resolution and photometric precision to define mineral electronic absorption bands. The reflectance for all lunar regions observed (over 100 to present) continues to increase toward longer wavelengths to at least 2.5 μm, and several mineral absorption bands appear. The telescopic spectra are of similar quality and contain features similar to laboratory spectra of lunar samples. The absorption features in several spectra have been quantitatively analyzed using newly developed computer processing techniques, including thermal flux removal and absorption band fitting, to produce these mineral identifications. Detection and quantitative analysis of these absorptions provide a much improved basis for remotely determining and mapping surface mineralogy quantitatively from the ground or using airborne or spacecraft platforms.

Radon emanation as an indicator of current activity of the moon

An interpretation of previously reported measurements of the Apollo 15/16 alpha-particle spectrometer on the distribution of 222Rn and 210Po across the lunar surface suggests that continuation of these measurements is a method of monitoring current activity on the moon. Since the two isotopes are relatively short-lived with effective half-lives of 3 days and 21 years, respectively, the activity detected has had to have been released during this current epoch. Changes in the rate of lunar emanation can be measured on three different time scales: (1) of a few days or less by detecting 222Rn at discrete sites such as the crater Aristarchus; (2) of a month by measuring 222Rn activity at the sunrise terminator; (3) of a few years by measuring 210Po activity at various locations. These observations could be carried out very effectively from a lunar polar orbiting satellite.

Detection of Radon Emanation from the Crater Aristarchus by the Apollo 15 Alpha Particle Spectrometer

The alpha particle spectrometer aboard the Apollo 15 command/service module was designed to detect alpha particles from radon decay and to locate regions with unusual activity on the moon. A significant increase in radon-222 activity was detected from a region containing the crater Aristarchus. The result is interpreted as probably indicating internal activity at the site. By analogy with terrestrial processes, increased radon emanation may be associated with the emission of other volatiles.

Stratigraphy of Ejecta from the Lunar Crater Aristarchus

Ejecta from lunar crater Aristarchus consist of mappable units that have different surface characteristics, lithologies, and geneses. Photogeologic mapping demonstrates that these units can be ordered into a stratigraphic succession representing stages in the emplacement of ejecta during a single impact event. Four main ejecta units are recognized: (a) a highly fractured rim unit consisting of an overturned flap of country rock, (b) a continuous ejecta blanket, (c) a zone of bright discontinous ejecta outside the continuous ejecta blanket associated with numerous secondary impact craters, and (d) a group of ejecta deposits on the rim which are genetically related to each other and include hummocky material (the hummocky rim unit), blocky lobes, and smooth flows. Other units, such as the ridged and leveed flows and the dark “lakes” or “playas,” are relatively younger than the ejecta and are only briefly discussed. The continuous ejecta blanket lies stratigraphically above the rim unit. To the east and south, the ejecta blanket has been stripped off the overturned rim unit by outward flowage from the crater during ejecta production, leaving parts of the rim eroded bare. Fall of large missiles to form the secondary craters and bright ejecta preceded the emplacement of the continuous ejecta. The general asymmetry of the continuous ejecta-blanket distribution appears to be related to the Aristarchus Plateau boundary fault, which may have controlled the way material was excavated. The hummocky rim unit only occurs on the northern and western rim and may be an overturned flap of premare Aristarchus Plateau bedrock not present near the surface on the southern and eastern rim of the crater. Blocky lobes and smooth flows mainly associated with the hummocky rim unit are interbedded, arguing that the smooth flows are part of the sequence of ejected rocks and are not younger volcanic flows.

Geologic interpretation of lunar data

The application of geologic concepts such as uniformitarianism and erosion cycles to lunar problems is illustrated by comparing terrestrial features and experiments with lunar features. Such comparisons include boulder tracks, blocky craters, volcanoes, and an experimental simulation of meteor bombardment. Lunar rock-stratigraphic units, lateral continuity, and superposition are illustrated using the crater Aristarchus. Reflection-emission data collected from the earth prior to unmanned and manned lunar exploration were remarkably good and captured the essence of the lunar surface at the fine scale. These data showed that the roughness of the lunar surface increased at the finer scale and that the lunar surface materials were porous and probably fragmental. Unmanned explorations significantly refined our knowledge of the lunar surface and its materials. In particular, unmanned soft-landing spacecraft obtained information on lunar topography and the physical properties and the chemical composition of the near-surface materials.

Tidal influences at the lunar crater Aristarchus

Observed temporary changes in the appearance of the lunar crater Aristarchus correlate remarkably well with times of the largest and smallest local tidal forces. Since tides are apparently triggering agents, most of the lunar events observed are probably active lunar phenomena. Conclusions indicate that tidal conditions at Aristarchus will be particularly favorable for events to occur on January 6 and 16, and February 2 and 12, 1970.

The moon in color

Color glows on the moon have been observed and photographed by a group of amateur astronomers working under contract for the National Aeronautics and Space Administration. The color was seen in the crater Aristarchus during a 4‐hr period before dawn on Nov. 15. A 16‐in telescope located at Port Tobacco, Md., was used.

On possible observations of luminescence on the dark side of the Moon

Attention is drawn to the fact that some early observations of “volcanoes on the Moon”, in the neighborhood of the crater Aristarchus, by William Herschel in 1787 bear rather striking resemblance to anomalous “lunar color phenomena” in the same region, reported more recently by Greenacre, Barr, and Hall from the Lowell Observatory. As Herschel's observations coincided in time with a maximum of solar activity, a hypothesis is tentatively proposed that both these phenomena, observed during lunar nighttime (Herschel) as well as in daylight (Greenacre et al.) are due to luminescence of the respective spots of the lunar surface excited by solar corpuscular radiation, in the former case moving through space along trajectories whose radius of gyration is large in comparison with the diameter of the Moon.

Volcanic Phenomena on the Moon

THE ejection of gas from the central peak of the Al-phonsus crater on the Moon observed on November 3, 1958, as well as the subsequent observations of the activity of this crater on October 23, 1959, have indicated that there are volcanic processes taking place on the Moon. It was established that molecular carbon was among the gases ejected. In cases of developed volcanic activity, such sporadic processes should be accompanied by a relatively steady ejection of gases of the fumarole emis sion type: indeed, observations made in November and December, 1961, showed the presence of such a fumarole field inside the Moon's Aristarchus crater.

Monochromatic Photography of Jupiter and Saturn

Photographs of the moon, which I made several years ago by means of ultra-violet light, revealed the existence of an extensive dark area surrounding the crater Aristarchus, which did not appear on plates made by means of yellow light, and could not be detected visually. Control experiments, made in the laboratory, made it appear probable that this deposit consisted of sulphur or sulphur bearing rock. It appeared to me probable that even more interesting results would be obtained in the case of the planets, especially Mars, and preliminary experiments were carried on during the past summer at my East Hampton Laboratory with a horizontal telescope of 56 feet focal length and 16 inches aperture, figured by Mellish, and nickel plated by the method described in the Astrophysical Journal for October. A deposit of nickel is necessary for the reason that silver reflects only 4% of the light in the region of the spectrum utilized, which lies between wave-lengths 3000 and 3300. This mirror was utilized in conjunction with a large Gaertner coelostat, which was placed at my disposal by the Naval Observatory. The mirror of this instrument was replaced by a 16-inch flat, also nickel plated, and photographs were made of the moon and Jupiter by means of infra-red, yellow, violet and ultra-violet light. Notwithstanding the fact that a moving plate holder, provided with eye-pieces for accurate following, was used, it was found difficult to secure sufficiently sharp definition, owing to the rather rapid periodic drift of the image which was very difficult to follow. The seeing moreover was not very good, and on the few nights when it was fair the mosquitoes were bad. Much valuable experience was gained however in the use of the monochromatic ray filters. In the earlier experiments on the moon, I used, for the ultra-violet ray filter, a rather thick deposit of metallic silver on uviol glass. This was abandoned in the present work, owing to its great opacity even for the ultra-violet region transmitted, and a rectangular glass cell, closed with plates of uviol glass, and filled with dense bromine vapor, used in its place. Such a cell, when used with an ordinary (i.e., not isochromatic) plate, gives a photographic image formed by wave-lengths below 3500 exclusively. By combining it with a thin layer of a very dilute solution of chromate of potash, the transmission is practically

Monochromatic Photography of Jupiter and Saturn

Photographs of the moon, which I made several years ago by means of ultra-violet light, revealed the existence of an extensive dark area surrounding the crater Aristarchus, which did not appear on plates made by means of yellow light, and could not be detected visually. Control experiments, made in the laboratory, made it appear probable that this deposit consisted of sulphur or sulphur bearing rock. It appeared to me probable that even more interesting results would be obtained in the case of the planets, especially Mars, and preliminary experiments were carried on during the past summer at my East Hampton Laboratory with a horizontal telescope of 56 feet focal length and 16 inches aperture, figured by Mellish, and nickel plated by the method described in the Astrophysical Journal for October. A deposit of nickel is necessary for the reason that silver reflects only 4% of the light in the region of the spectrum utilized, which lies between wave-lengths 3000 and 3300. This mirror was utilized in conjunction with a large Gaertner coelostat, which was placed at my disposal by the Naval Observatory. The mirror of this instrument was replaced by a 16-inch flat, also nickel plated, and photographs were made of the moon and Jupiter by means of infra-red, yellow, violet and ultra-violet light. Notwithstanding the fact that a moving plate holder, provided with eye-pieces for accurate following, was used, it was found difficult to secure sufficiently sharp definition, owing to the rather rapid periodic drift of the image which was very difficult to follow. The seeing moreover was not very good, and on the few nights when it was fair the mosquitoes were bad. Much valuable experience was gained however in the use of the monochromatic ray filters. In the earlier experiments on the moon, I used, for the ultra-violet ray filter, a rather thick deposit of metallic silver on uviol glass. This was abandoned in the present work, owing to its great opacity even for the ultra-violet region transmitted, and a rectangular glass cell, closed with plates of uviol glass, and filled with dense bromine vapor, used in its place. Such a cell, when used with an ordinary (i.e., not isochromatic) plate, gives a photographic image formed by wave-lengths below 3500 exclusively. By combining it with a thin layer of a very dilute solution of chromate of potash, the transmission is practically

Monochromatic Photography of Jupiter and Saturn

Photographs of the moon, which I made several years ago by means of ultra-violet light, revealed the existence of an extensive dark area surrounding the crater Aristarchus, which did not appear on plates made by means of yellow light, and could not be detected visually. Control experiments, made in the laboratory, made it appear probable that this deposit consisted of sulphur or sulphur bearing rock. It appeared to me probable that even more interesting results would be obtained in the case of the planets, especially Mars, and preliminary experiments were carried on during the past summer at my East Hampton Laboratory with a horizontal telescope of 56 feet focal length and 16 inches aperture, figured by Mellish, and nickel plated by the method described in the Astrophysical Journal for October. A deposit of nickel is necessary for the reason that silver reflects only 4% of the light in the region of the spectrum utilized, which lies between wave-lengths 3000 and 3300. This mirror was utilized in conjunction with a large Gaertner coelostat, which was placed at my disposal by the Naval Observatory. The mirror of this instrument was replaced by a 16-inch flat, also nickel plated, and photographs were made of the moon and Jupiter by means of infra-red, yellow, violet and ultra-violet light. Notwithstanding the fact that a moving plate holder, provided with eye-pieces for accurate following, was used, it was found difficult to secure sufficiently sharp definition, owing to the rather rapid periodic drift of the image which was very difficult to follow. The seeing moreover was not very good, and on the few nights when it was fair the mosquitoes were bad. Much valuable experience was gained however in the use of the monochromatic ray filters. In the earlier experiments on the moon, I used, for the ultra-violet ray filter, a rather thick deposit of metallic silver on uviol glass. This was abandoned in the present work, owing to its great opacity even for the ultra-violet region transmitted, and a rectangular glass cell, closed with plates of uviol glass, and filled with dense bromine vapor, used in its place. Such a cell, when used with an ordinary (i.e., not isochromatic) plate, gives a photographic image formed by wave-lengths below 3500 exclusively. By combining it with a thin layer of a very dilute solution of chromate of potash, the transmission is practically