. The Aristarchus plateau, Rima BodeGruithuisen Domes & Moscoviense

Irregular Mare Patches/Ina Caldera

Credit: http://lroc.sese.asu.edu/images/videos

 
 

 
 

 
 
 
 
 
 

The Aristarchus plateau - 50°W, 25°N

The Aristarchus crater is located on the edge of the Aristarchus Plateau, one of the most geologically interesting regions of the Moon. This complex impact crater of 40 km wide and 3.5 km deep has been probably formed 175 million years ago.

The impact straddled the boundary of the plateau and the surrounding mare, thus excavating both very different rock types, as well as underlying crustal rocks.

 
 

TheAristarchus Central Peak show a diversity of features

The high albedo material is most likely a common lunar rock type, anorthosite, while the dark areas is basalticWhat is the dark material exposed in the Aristarchus central peak? Scientists are not sure, however we know the adjacent Aristarchus plateau is blanketed in dark pyroclastic deposits. 

A close up view of the Aristarchus Central Peak. Image is 700 m wide, NAC M122523410. Credit: NASA/GSFC/Arizona State University.

Aristarchus crater floor

Look closely at the early afternoon lighting WAC mosaic; you can clearly see that some of the Aristarchus ejecta has high reflectance, and some has low reflectance. This contrast reflects the compositional difference between the target rock. The northwest portion was mostly basalt and ash, while the south-southeast was predominantly crustal rocks (anorthosite and/or granite).

West wall of Aristarchus crater seen obliquely by the LROC NACs from an altitude of only 26 km. Scene is about 12 km wide at the base. Image NAC M175569775. Credit: NASA/GSFC/Arizona State University.

The floor of Aristarchus crater provides explorers a unique opportunity to study a wide variety of lunar rocks and geologic processes, possibly including how lunar granite forms. Diverse materials such as dark, multilayered mare basalts in the walls, bright crustal rocks in the central peak, impact melt, and even regional pyroclastic materials blanketing the crater are brought to the floor and accummulated through mass wasting. All these features creates a bountiful trove of geologic materials.

Field of striated boulders on the wall of Aristarchus crater. Uphill is towards top of image. (100 meters) LROC NAC image M120161915 [NASA/GSFC/Arizona State University].

The impact straddled the boundary of the plateau and the surrounding mare, thus excavating both very different rock types, as well as underlying crustal rocks.

 
 

Field of striated boulders

Future astronauts exploring Aristarchus crater could easily sample materials from the highest point of the Central Peak without having to climb to the summit. They will simply browse the samples delivered at the base!

Just above-left, an oblique (-67.03° off nadir) view of sunrise within the deep interior of the famous Cobra Head of Schröter Valley on the Aristarchus Plateau. Check at the right for a global view.

Credit: lroc.sese.asu.edu / The LROC NAC right-video has been taken the 2010-03-06 at 14:02:24.346 UTC. The video features high definition flyover of the central peak of Aristarchus crater, near a Constellation region of interest.

 

 

The right Image show a LROC WAC regional view of Aristarchus plateau and crater.

From LROC WAC color images you can see that the gray streaks show up as distinct color anomalies, color due to variations in rock type. The area has long been known to be among the reddest spots on the Moon - meaning its reflectance strongly increases from short to long wavelengths. In the WAC color image below, you can see the distinct red-hued region, which is largely blanketed by the glass-rich products of explosive volcanic eruptions. This area is surrounded by bluer terrain, which formed when titanium-rich (at least it is thought that titanium is in these rocks) lava flowed across the surface and flooded the area, forming a portion of Oceanus Procellarum. In both of the WAC context images, you can see Vallis Schröteri, a canyon-like feature known as a sinuous rille, through which the lava once flowed.

NAC Frame M111945148R. Part of the vast pyroclastic deposit near a Constellation Program Region of Interest located on the Aristarchus plateau is visible in this image. View is 537 m across [NASA/GSFC/Arizona State University].

A typical view of the lunar surface? Hardly! This NAC frame (537 m across) reveals a dark, fine-grained pyroclastic deposit that has mantled older units, including flat mare deposits (at left) and nearby knobs of highland materials (at right). This site (Aristarchus 2) is located in the northwest region of the Aristarchus Plateau, within the most extensive deposit of pyroclastic materials on the Moon. The Constellation objectives here (Aristarchus 2) are more focused on resource potential, whereas Aristarchus 1 was selected more on the basis of geologic diversity.

At Aristarchus 2, some areas of the mantling deposit are estimated to be 10 to 20 meters in thickness. In the small area shown in the above image, the deposit is much thinner (likely only a meter or two deep). The bright-rayed crater at right-center (15 m diameter) has penetrated the mantle and exposed fresh, light-colored rocks typical of the lunar highlands. Many of the craters at left, although similar in size to the bright-rayed crater, have uncovered only dark materials that are slightly lighter in color than the pyroclastic mantle. Such exposures of rock by fresh craters provide some of the best clues to the composition and distribution of covered units and help to reconstruct the history of events that created the deposits we see.

Lunar pyroclastic deposits are formed by explosive eruption of basaltic magma and are thought to be associated with early stages of eruption of the mare deposits that fill impact basins across the near side. The deposits appear fine-grained and often very dark, and they have been called "mantling deposits" because they drape over and obscure underlying terrain. This mantling effect is similar to what you see after a deep snow: normally sharp edges of tables, chairs, and cars are now smoothed and subdued. The same effect happens under a blanket of fine ash.

Pyroclastic mantling deposits were sampled by the Apollo astronauts at several sites on the Moon, and in particular a deposit of submillimeter-sized orange glass and crystallized beads was discovered near Shorty Crater by Astronaut Harrison "Jack" Schmitt in the Taurus-Littrow Valley during the Apollo 17 mission. The beads at Apollo 17 formed from magma that originated ~400 km deep within the Moon and erupted more than 3.6 billion years ago.

Pyroclastic deposits are fascinating to lunar scientists because of the possible economic and engineering value of the volatile and metallic elements identified on and within their component beads. The beads have trapped solar wind hydrogen and Helium-3, and enrichments of volatile elements such as sulfur, lead, fluorine and zinc have been measured on their surfaces. Pyroclastic deposits are typically rich in iron oxides and also have widely varying amounts of titanium oxide, commonly present as the mineral ilmenite. Areas with pyroclastic deposits are likely to feature prominently among future exploration sites on the Moon and are a key enabler for large-scale human lunar habitation. Thus, it is important that we learn as much as we can about them. Where are they, how thick are they, and do compositions vary within a deposit and from deposit to deposit?

Rima Bode - 3.5°W, 12°N

Rima Bode is a spatially extensive (~7000 km2) dark mantling deposit produced by fire fountaining, possibly composed of black glass, as indicated by its very low albedo. The deposit is embayed by ~3.5 Ga maria, indicating that these pyroclastics are potentially ancient. 

Rima Bode is an extensive, high-Ti pyroclastic deposit, which potentially contains volatiles both from the mantle and from solar wind implantation. A mission to Rima Bode could assess the pyroclastic concentrations in mature, high-Ti pyroclastic deposits.

The lunar environmental effects on human life, especially the radiation environment, could be mitigated by studying the radiation shielding effects of fine grained pyroclastic materials.

A mission to Rima Bode would provide the opportunity to study dust mitigation of mature, fine-grained pyroclastic deposits, and how to use these deposits to support and potentially enable long-term human presence on the lunar surface.

A key measurement will be the chemical composition of the pyroclastic deposit, Bulk H2 in upper meter of regolith, quantify its geo-mechanical properties. A potential sample return mission of the pyroclastic materials, once in-situ data have defined the variability in the deposit, will be a possibility.

It is recommended a short lived (less than 1 lunar day) landed mission on the dark mantle deposit to analyze chemical composition and volatile content of the pyroclastics.

N.B. About Image: Co-registered Lunar Orbiter mosaic (LO-IV 109H2) and Clementine color-ratio (R=750/415, G=750/950, B=415/750) mosaics of the Rima Bode region of the Moon.

Gruithuisen Domes - 36.5°N, 40.2°W

The Gruithuisen Domes are located on the western edge of the Mare Imbrium in the northwestern portion of the Procellarum KREEP terrane.

Their unique morphological surface suggests that the lava flows that produced the domes were highly viscous.

The Lunar Prospector GRS data and the spacecraft Clementine multi-spectral data show that, these domes are relatively low in Fe0 with 6-8 wt%, and high in Th contents with 43 +/-3 ppm for Gruithuisen Gamma and, 17 +/-6 for the Delta.

Photometric observations and the Diviner Spectral data confirm that, these domes are made of silicic . Learn more Here

 

. Exploration mission with a lander on the flat summit of the Gruithuisen Gamma, or the Delta dome could document the unique morphological, mineralogical, elemental, and petrological characteristics of the surface in order to resolve thepetrogenesis and the thermal evolution of the Moon.

... This mission could serve as a precursor to a sample return to Earth.

. Exploration mission with a rover will be regional.

 

Moscoviense - 147°E, 26°N

TheMoscoviense Basin. (Left) LROC WAC base map with LOLA shaded topography.(Right) LOLA-derived slopes.

Moscoviense basin on the far side of the Moon is a Nectarian-aged multi-ring impact basin that formed 3.85-2.92 Ga. The basin contains an elongated floor with non-concentric basin rings. The basin contains some of the thinnest crust on the Moon, although it is located in the relatively thicker crust of the lunar highlands. The basin contains a deposit of mare, a pyroclastic deposit, and several lunar swirls. The basin contains geologic diversity, including orthopyroxene, olivine, and Mg-Al Spinel in an anorthosite-rich peak ring which may have originated from differentiated magmatic intrusions into the lower crust, potentially near the crust/mantle boundary. The mare within the basin is also diverse, including low and high FeO, low and high TiO2, and possibly high alumina.

The diversity of crustal materials present in the basin will allow us to constrain the bulk composition of the Moon.

The secondary crust present in the form of mare and pyroclastic deposits provide a glimpse of the far side planetary interior and the process of thermal evolution. In addition, the thin crust in the region may provide unique access to lower crustal or mantle materials at the surface. The presence of impact craters, swirls, wrinkle ridges, and various volcanic units can be studied to better understand how planetary surfaces are modified by geologic processes. The presence of several lunar swirls and a pyroclastic deposit may help constrain the lunar water cycles and the form and concentration of volatiles on the lunar surface.

The Moscoviense pyroclastic deposit, diverse mare units containing high Fe and Ti, and the lunar swirls will allow for analyses of the lunar resource potential and potential useful resources to be extracted.

An example of a mission with traverse could include regional roving experiments that investigate the peak ring/western basin floor for lunar swirls and pyroclastic deposits. A sample return mission could include a diverse suite of samples such as basin impact melt, lower crust mafic minerals (including Mg-Al spinel), pure anorthosite, and/or farside mare basalts.