. Landing on the Schrödinger basin,  the second youngest basin on the Moon

A study of Kohout and al. – 40th Lunar and Planetary Science Conference (2009)
& Nördlingen Ries Crater Workshop (2010)

About the video: On 15 January 2012 the Lunar Reconnaissance Orbiter slewed 64.5 degrees to the east to capture this astonishing view of the floor and central peak of Tycho crater. In June of 2011, LRO captured a view looking to the west. Check it out: http://www.youtube.com/watch?v=361YcacQZjg More amazing LROC images can be found at http://lroc.sese.asu.edu.

 
 

 
 

 

The Schrödinger basin - 135°E, 75°S

The lunar farside — that mysterious face of the Moon hidden from Earth – contains a cache of clues about how the Earth formed, how planets evolved, and how volcanic and impact cratering processes reshaped the Solar System. The farside of the Moon holds the key to the earliest bombardment of the Earth and whether impact cratering processes were involved in the origin and earliest evolution of life on Earth.

The oldest and largest impact basin on the Moon is nearly 2,500 kilometers in diameter and stretches from the South Pole to a tiny crater called Aitken. This South Pole-Aitken basin (also called SPA basin) is one of the leading targets for human and human-assisted robotic exploration. A particularly rich scientific and exploration target within that basin is the Schrödinger basin, about 320 kilometers in diameter, and located towards the south polar end of the South Pole-Aitken basin.

Scientists and engineers are already designing the methods for a mission to Schrödinger that collects samples and brings their extraordinary secrets back to Earth for study. To give you a perspective of this mission, we have created a video and soundtrack that carries you to the Moon, around the South Pole-Aitken basin, and to a first landing site within the Schrödinger basin. We hope this is the first step in an exhilarating mission of discovery.

Credit: This flyover was conceptualized and produced by Dr. David A. Kring. The Lunar Reconnaissance Orbiter Camera data was assembled and rendered by Dr. Debra M. Hurwitz. Modeling and animation were implemented by John Blackwell. The music on the sound track is Darkest Night by Pond5 and used with permission. / Lunar and Planetary Institute

Second youngest large basin on the Moon, the Schrödinger impact basin include variety of geologic features available that could be interesting for future exploration. Often, boulders in Schrödinger come from regions that are not easily accessible by robotic equipment or humans. The above image highlights a distribution of boulders near the base of a part of the central peak ring, located at 77.196°S and 133.178°E.

Boulders >1 m across, and a few trails, surround the base of a mountain in the Schrödinger central peak ring. Boulder in lower left is ~55 m across. Image NAC M187340587LR is width of 732 m. [NASA/GSFC/Arizona State University].

Boulders rolled down an incline on a terrace near the Schrödinger basin rim. Boulders are ~20 to 30 m in size. The LROC NAC M159017963R image is width of ~1.2 km, and is showing in down slope direction to upper left. [NASA/GSFC/Arizona State University].

When scientists and engineers brainstorm landing site locations for future lunar missions - robotic or human - they must consider numerous factors as the technology and equipment that will land the mission on the Moon and the scientific and resource interest of a location.

LROC images, as well as the data from other instruments aboard LRO, provide scientists and engineers the means to study the lunar surface at high-resolution. Future missions can then take truly advantage of the rich geology of the Moon.

When Schrödinger has impacted into the South-Pole Aitken (SPA) rim material, it may have sampled some of the deep lunar crust excavated by its host impact. Schrödinger basin is located on the rim of the SPA basin at 79.13°S and 140.60°E. If it is true, the smooth deposits on the basin floor may be a combination of both impact melt and volcanic material. There are also several pyroclastic vents located within the basin, suggesting that at least some episodes of volcanic activity in the basin had high volatile contents.

On the left image, a portion of eroding basin wall terrace material is showing. Several boulders around 30 m in diameter rolled downhill from a boulder cluster. Their original locations may be derived using the prominent boulder trails left behind during their downhill descent. Sampling these boulders would be particularly useful during a future mission because they represent material from the basin rim and do not require an astronaut or rover to traverse to the higher elevations.

Schrödinger boulders

Schrödinger basin rim

Ejecta blancket features.

Scrödinger impact crater

Dozens of boulders, ranging from 10 m to more than 30 m in diameter, are distributed within an ejecta ray close to the crater rim (lower right). These boulders represent the deepest material excavated during crater formation. LROC NAC M159013302LR, image width is ~850 m [NASA/GSFC/Arizona State University].

Schroïdinger has a diameter of 315 km, a depth of 4,5 km, and a prominent inner peak ring that rises at 1-2,5 km above the basin floor. what that makes it an ideal location for a future landing site is that, it may have tapped deep chrustal lithologies associated with SPA-forming impact.

The opportunities for Human Exploration

Located near the South Pole on the lunar far side, it is the second youngest impact basin (after Orientale) and, thus, remains well exposed for scientific study. Schrödinger intersects the pre-Nectarian Amundsen-Gainswindt basin (AG), as well as the inner rings of the South Pole-Aitken (SPA) basin. Modeling suggests that Schrödinger’s inner ring originates from a depth of 1030 km and, therefore, might contain indigenous SPA materials. Additionally, at least three volcanic units, deep fractures, ghost craters, and secondary craters can be found within the basin. The floor contains two impact melt lithologies, a rough plains unit and a smooth plains unit, resulting of two types of lunar volcanism: mare balsalts and pyroclastic.

For the authors, major scientific goals can be accomplished within Schrödinger, specifically those from the National Research Council lunar science priorities. For this basin that will be to determine the ages of the impact event and the material from its inner ring. In the case that SPA material is uplifted there, the SPA event can be dated allowing to anchor the Earth-Moon impact flux curve. Also, studying the material produced by various basaltic volcanic events (Upper Imbrian and Eratosthenian in age), the deep seated explosive volcanism (Eratosthenian or Copernican in age), the potential products of crustal and mantle degassing along deep fractures, as well as the ghost craters flooded by a melt sheet, and the secondary craters on the basin floor.

To be able to reach those goals, they propose a landing site for human exploration on a relatively smooth terrain within the inner ring of Schrödinger – either on the exposed melt sheet or on one of the basaltic units. Such a location will provide access to the features outlined above and meet a planned ~20 km extra vehicular activity (EVA) limit . Based on geological mapping and Clementine images, they evaluated three landing sites where at least 4 of the scientific objectives can be accomplished.

In general, young basins have well exposed rims, inner rings, and proximate ejecta composed of melt breccia enabling relatively easy sampling. In contrast, rim structures and ejecta of old basins are eroded and covered by superposed ejecta of younger basins (forming a magaregolith layer). In these cases the central melt sheet may provide the most reliable source of sampling material. The central melt sheet is often buried under regolith as well and in most cases it is additionally covered by mare basaltic flows. However, as will be outlined below, young impact events of sufficient size may penetrate the regolith and mare basalt layers and expose the underlying melt sheet for sampling.

The first landing site is located on the northern part of the Schrödinger melt sheet where a basaltic unit is superimposed. This relatively smooth terrain should ensure safe landing conditions. The basaltic unit might be the first sample station. It is approx. 5 km across in its shorter dimension and, thus, can be completely traversed before proceeding farther south to one of two facies of Schrödinger’s melt sheet, providing a second point of interest within a single EVA. A second EVA to the southwest provides access to a second basaltic unit. A third EVA towards the west of the landing site will take crew to the second of the two melt facies and to one of the deep fractures on the basin floor. From those stations, crew can move north to Schrödinger’s inner ring. Additionally, an Orientale secondary crater is located east of one of the basaltic units in a rougher terrain that could be targeted by additional EVA’s .

A second landing site is located in the western part of the Schrödinger’s melt sheet, near two large ghost craters that appear to have been flooded by the melt sheet during the complex formation of the basin. This provides the first opportunity for crew to study the morphology of a ghost crater and the thickness of a basin melt sheet. Towards the east, a ridged terrain of unknown origin as well as Antoniadi secondary craters can be reached. Towards the west, Schrödinger’s inner ring is accessible for additional sampling of potential SPA material.

The Clementine Image of the Schrödinger basin with the geological map. the three landing sites and corresponding 10 km EVA radius ( of a 20 km return trip) are outlined in white. the yellow number correspond to the following scientific goals of interest: 1- the melt sheet, 2-the inner ring, 3-the basaltic units, 4-the explosive volcanic unit, 5-the deep crustal fracture, 6-the ghost craters, 7-the secondary craters and, 8-the ridged terrain.

A third landing site is proposed in the southeastern part of the basin to study an explosive volcanic unit. The central volcanic crater, as well as crustal fractures through which magma may have migrated towards the surface, occur within EVA limits. Additionally, Schrödinger’s inner ring is accessible to the southeast and Antoniadi secondary craters occur towards the west. One of the impact melt facies is located near the landing site and, if routes across basin fractures can be found, the other facies can also be reached. This option, however, must be evaluated with additional work. The use high-resolution imagery, spectroscopic data, and digital elevation models can be used within a Geographic information system (GIS) to identify locations of high interest for EVA. In addition, a GIS can be used to assess potential EVA routes and to maximize hazard avoidance by characterizing surface parameters (i.e., slope angle, slope aspect, roughness, composition, etc.) prior to surface operations [6].

Additionally, a precursor robotic rover can reduce the risk, requirements, and cost of a human exploration [7, 8] and provide site characterization to enhance the efficiency of human exploration by identifying the highest priority traverse stations. It could also collect and deliver samples from remote areas to the human mission landing site or conduct complementary research after the human mission departure [7, 8].

The lunar history with the Schrödinger's stratigraphic units*

*T. Kohout and al. - Nördlingen Ries Crater Workshop (2010)

This impact site is the second youngest basin-forming event and lies within the South Pole-Aitken Basin (SPA), which is the oldest and largest impact basin on the Moon. Thus, landing sites within Schrödinger should provide access to impact lithologies with ages of each event, providing a bracket of the entire basin-forming epoch and resolving both of the leading science priorities [2]. Additionally, the floor of Schrödinger Basin has been partially covered by younger mare and pyroclastic units. The volcanic materials, as well as impactexcavated and uplifted units, will provide chemical and lithologic samples of the lunar crust and potentially the upper mantle.

The authors proposes a landing site for manned or robotic exploration on a relatively smooth terrain within the inner ring of Schrödinger – either on the exposed melt sheet or on one of the basaltic units.

Based on geological mapping and Clementine images, they have evaluated three landing sites where most of the scientific objectives can be accomplished. The white circles, in the below picture, outline a 10 and 20 km radius of an EVA range activities.

Clementine image of the Schrödinger basin with superimposed geological map by [3]. White bar is 50 km long, white dots are landing sites, and white circles are 10 and 20 km radii. The main units are smooth plains material (sp), rough plains material (rp), basin wall material (bw), hummocky material (h), peak ring material (pr) mare material (m), dark explosive volcanic material (dm), and ridged terrain (r). The sp unit is interpreted to be Schrödinger impact melt, and the rp unit to be Schrödinger impact melt breccia.

The Schrödinger Basin provides a diverse suite of scientific opportunities because of the proximity of different geologic units and its relatively good preservation. Any one of three possible landing sites will provide the first samples of basin melts of undisputable basin origin and potentially melts of SPA origin. In addition, at least two types of younger volcanism (and magmatic source regions) can be studied in the area.

THE VERTICAL EXTENT AND STRUCTURE OF THE MEGAREGOLITH

The lunar megaregolith is thought to be the product of the relatively short-lived Late Heavy Bombardment (LHB), or lunar cataclysm, early on in the moon‘s geological history (Hartmann, 1973). The large impacts responsible for the formation of the lunar basins would have excavated, mixed and fractured the lunar surface to a potential depth of several kilometers. This layer of the crust has been defined by several researchers as the highly fragmented layer, composed of basin ejecta, that is directly above the fractured bedrock . 

Later, smaller meteoroid impacts (post-LHB) would have pulverized and mixed the very top layer of the crust (the regolith) but would have had a negligible effect on the overall structure of the megaregolith (Hartmann, 1973; Head, 1976).

Current estimates are 1-2 km for the near side mare region, 5-10 km for the highlands and 1-2 km for the South Pole-Aitken region. The thickest megaregolith should be found at the margins of the major basins, because this is where most ejecta was deposited (Mcgetchin, 1973). High-quality absolute thickness measurements at several locations on the lunar surface is essential to validate, previous estimates and to constrain geophysical models of the Moon‘s evolution. The next sections outline target sites requirements for such measurements and suggest landing sites based on those requirements and on the currently available lunar datasets.

By targeting deep craters for which the estimated structural uplift is greater than the estimated megaregolith thickness (1–2 km for maria, 5–10 km for highlands, 1–2 km for SPA), it should be possible to investigate and characterize the structure and composition of deeper levels of the megaregolith. This information could be used along with other measurements (e.g., seismic data) to obtain a more accurate megaregolith thickness.

Schrödinger provides access to nearly every layer of planetary differentiation models. The large basin lies within the thin crust of the SPAT, and its large size implies that it would most likely sample mantle material in the melt. In addition, this mantle material may also be exposed within the stratigraphic uplift of the peak rings.