Marius Hills Skylight hazard characterization as a possible landing site for lunar subsurface exploration

Marius Hills Skylight hazard characterization as a possible landing site for lunar subsurface exploration
R. Pozzobon1, A. P. Rossi2, S. Ferrari1, M. Massironi1, M. Pajola3, A. Nüchter4, D. Borrmann4, J. Zevering4, A.
Bredenbeck4, F. Arzberger4, C. A. Reyes Mantilla4, F. Maurelli2, V. Unnithan2, H. Dreger2, K. Mathewos2, N.
Pradhan2, C. Pernechele3, L. Paoletti3, E. Simioni3., T. Santagata5.
1University of Padova, Italy, 2Jacobs University Bremen, Germany, 3INAF Padova, Italy, 4University of Würzburg, Germany, 5Vigea Virtual
Geographic Agency, Italy
Introduction: The renewed interest in the crewed and
robotic exploration of the surface and subsurface of the
Moon has significantly increased over the past few
years among the scientific community and space
agencies. The NASA Artemis program and the ESA
EL3 (European Large Lunar Lander) represent new
steps in this direction. Such exploration requires further
technology developments in parallel with new landing
sites characterization. In particular, the exploration of
the lunar subsurface by accessing lava tubes from
skylights has been subject for ESA call for ideas in its
Open Space Innovation Platform in the SysNova Lunar
Caves system studies framework. In this light we
present some preliminary landing site assessments
performed as a support for the DAEDALUS (Descent
and Exploration in Deep Autonomy of Lava
Underground Structures) [1] mission design proposal, to
be deployed in the Marius Hills region where a lunar
skylight with underlying void has been discovered [2].
The exploration of the Marius Hills lava tube is tied to
the possibility to land, rove and safely approach the
skylight. Therefore, it is pivotal to characterize in high
detail the terrains surrounding the skylight both in terms
of science and hazard/safety. In terms of accessibility,
the skylight should be surrounded by obstacle-free
terrains presenting a relatively low number of boulders,
while the regolith should be able to sustain inertial
platforms with a relevant mass. In addition, the location
should guarantee an easy approach to the pit up to a
location where the DAEDALUS sphere will be
deployed. Therefore, in order to characterize the
feasibility of landing, approach and deployment of the
DAEDALUS sphere several aspects of the terrains
surrounding the pit must be investigated considering
several morphometric parameters:
- flat surface over steep overhanging pit margins,
with a slope safety margin of 15°;
- hazard-free or low-hazard trafficability from
landing ellipse to the pit;
- hazard free landing area (low crater density, low
slopes, boulder-free);
- closest access point to the skylight edge.
Geologic context: Marius Hills region is among the
largest volcanic complexes on the Moon and is located
in the Oceanus Procellarum. Beside the presence of
multiple monogenic cones set on a ~300 km shield, this
location is characterized by widespread mare basalt and
very large rilles at its flanks, namely “Rille A and
“Rille B [3]. The selected skylight is a nearly circular
hole of ~65 m in diameter, located at 303.3°E, 14.2°N
in the Marius Hills region in the middle section of the
Rille A. The first detection was achieved via SELENE-
Kaguya Terrain Camera images [1] whose first depth
estimate was of ~80 m, subsequently refined to be ~45
m [4].
Data and methods: The landing site has been
characterized on a bundle-adjusted LROC NAC [5]
stereo DEM (4 meters of resolution) refined with the
shape from shading technique. This allowed us to
retrieve the highest possible detail in the topography and
detect small features at high resolution.
We refined the DEM and focused our attention in an
area of 1 km2 centered on the pit.
Hazard characterization: We performed
morphometric analyses on the refined DEM using the
multi-scale TPI (Topographic Position Index), that
allows to extract raised and depressed areas with respect
to the surroundings. In this way, together with LROC
NAC orthoimage analysis, we were able to characterize
the following hazards:
- Crater density: Of all craters we identified,
some of them are not hazardous as they may be
very shallow (few decimeters per meter in
diameter, slopes being negligible);
- Slopes: slopes thresholds represent the major
trafficability constraint on the area. Based on
both HERACLES [6] and MSL Curiosity we
selected a maximum slope safety threshold to
be <15°. A safer buffer in slope threshold was
set at <10°
- Craters’ depths: craters shallower than 1 m
and with inner slopes <15° are considered safe.
- Boulder abundance: less than 50 boulders are
present in the area, none implying any hazard.
The final result is a hazard map (see fig. 1) with safe
areas for landing and trafficability, low hazard and no-
go areas.
Skylight characterization: Since the objective of the
SysNova system study call is the deployment of a
robotic device inside the lunar cave for horizontal
exploration, we attempted to characterize also the cave
1886.pdf52nd Lunar and Planetary Science Conference 2021 (LPI Contrib. No. 2548)
floor. In order to identify the sizes of the boulders
located on the floor of the sinkhole (remnants of the
collapsed ceiling) we made use of an LRO/LROC-NAC
image (M155607349RE) with a spatial scale of 0.42 m
and with a solar incidence angle of ~12°. We were
therefore able to map and evaluate the boulder
abundance and size [7] (up to ~1.5m also in elevation)
with the same methodology. Overall, our preliminary
results found the best sector to deploy a device in the
NW of the skylight floor (white square in fig. 2).
Results and Discussion: From our analysis of the
Marius Hill skylight surroundings it appears that
trafficability is not affected by whatsoever obstacles
such as boulders, and landing should be sufficiently safe
in terms of engineering constraints: the slopes are <10°
in most of the area and the no-go zones are limited to
few impact craters and depressions apart from the
skylight itself and secondarily by the rim of the Marius
Hills Rille A. By using low incidence and low phase
angle LROC NAC images we were able to observe and
characterize the bottom of the cave and retrieve the
boulder abundance and their size. Although most of the
floor is characterized by a pile of large boulders and
regolith, the northwestern portion should be sufficiently
safe to be approachable from above and to deploy a
robotic device with chances of navigation and mapping.
[1] D. Borrmann, A. Nüchter and the DAEDALUS team.
Lunar Caves Exploration with the Daedalus Spherical Robot.
In 52nd Lunar and Planetary Sci- ence Conference (LPSC
2021), 2021
[2] Haruyama et al., 2009, Possible lunar lava tube skylight
observed by SELENE cameras. Geo- physical Research
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[3] Besse, S. et al.. «Compositional Variability of the Marius
Hills Volcanic Complex from the Moon Mineralogy Mapper
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Figure 1: Hazard analysis preliminary map
characterized on shape from shading refined DEM. A
putative landing ellipse is placed in the safest possible
area and the low hazard are highlighted (in orange and
red respectively). The skylight is highlighted in white.
Figure 2: LROC NAC image (M155607349RE, 0.42
m/pixel) with visible boulders on the floor mapped with
circles (in red in image 2 and black in image 3). The
heatmap highlights the boulder density weighted on
their diameter. The yellow circles mark the boulder
presence on the surface. The white square marks the
area where it is possible to deploy a device with
acceptable hazard.
1886.pdf52nd Lunar and Planetary Science Conference 2021 (LPI Contrib. No. 2548)
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Full-text available
1] We discovered a vertical hole on the Moon, which is a possible lava tube skylight, using data from SELENE's two high-resolution cameras: the Terrain Camera and the Multi-band Imager. The hole is nearly circular, 65 m in diameter, and located in a sinuous rille at the Marius Hills region, a volcanic province on the lunar nearside. We observed the hole at various solar illumination conditions and estimated its depth to be 80 to 88 m. The depth/diameter ratio is much larger than for typical impact craters. There are neither conspicuous deposits indicating volcanic eruptions from the hole, nor are there pit craters adjacent to the hole that could be related to an underlying fault or dike. The area around the hole is covered by a thin (20 to 25 m) lava sheet, which may help protect the lava tube from collapse due to meteorite bombardment. Citation: Haruyama, J., et al. (2009), Possible lunar lava tube skylight observed by SELENE cameras, Geophys. Res. Lett., 36, L21206, doi:10.1029/2009GL040635.
Typical flow thicknesses of lunar mare basalts were not well constrained in the past, because as craters and rilles age, downslope movement of loose material tends to mix and bury stratigraphy, obscuring the three dimensional nature of the maria. New Lunar Reconnaissance Orbiter Camera high resolution images unambiguously reveal thicknesses of mare basalt layers exposed in impact craters, rilles, and steep-walled pits. Pits up to one hundred meters deep present relatively unmodified, near-vertical sections of mare in three cases, and many young impact craters also expose well preserved sections of mare. Oblique views of each pit and many of these craters reveal multiple layers, 3 to 14 m thick, indicating that eruptions typically produced a series of $ 10 m thick flows (or flow lobes) rather than flows many tens to hundreds of meters thick. Additionally, these images unambiguously show that the floors of two pits extend beneath the mare surfaces, thus revealing sublunarean voids of unknown lateral extent. We also document the occurrence of pits that may be expressions of collapse into subsurface voids in non-mare impact melt deposits. These voids are compelling targets for future human and robotic exploration, with potential as temporary shelters, habitations, or geologic museums.
The Lunar Reconnaissance Orbiter Camera (LROC) Wide Angle Camera (WAC) and Narrow Angle Cameras (NACs) are on the NASA Lunar Reconnaissance Orbiter (LRO). The WAC is a 7-color push-frame camera (100 and 400m/pixel visible and UV, respectively), while the two NACs are monochrome narrow-angle linescan imagers (0.5m/pixel). The primary mission of LRO is to obtain measurements of the Moon that will enable future lunar human exploration. The overarching goals of the LROC investigation include landing site identification and certification, mapping of permanently polar shadowed and sunlit regions, meter-scale mapping of polar regions, global multispectral imaging, a global morphology base map, characterization of regolith properties, and determination of current impact hazards. KeywordsLRO-LROC-Instrument-Camera-Moon-Lunar-Calibration
Lunar Caves Exploration with the Daedalus Spherical Robot
  • D Borrmann
D. Borrmann, A. Nüchter and the DAEDALUS team. Lunar Caves Exploration with the Daedalus Spherical Robot. In 52nd Lunar and Planetary Sci-ence Conference (LPSC 2021), 2021
«HERACLES -Exploring the Moon in an International Context», s.d
  • M Landgraf
  • William Carey
  • Hipkin
  • Carpenter
  • Hiesinger
Landgraf, M, William Carey, V Hipkin, J Carpenter, e H Hiesinger. «HERACLES -Exploring the Moon in an International Context», s.d., 4.
  • M Pajola
Pajola, M., et al.,. «Boulder Abundances and Size-Frequency Distributions on Oxia Planum-Mars: Scientific Implications for the 2020 ESA ExoMars Rover». Icarus 296 (1 novembre 2017): 73-90.