THE GEOLOGY OF THE LUNAR NORTH POLE:
MINERALOGY AND PREVIOUSLY UNIDENTIFIED MARE MATERIAL
Laura M. Corley
Department of Geology and Geophysics
University of Hawai‘i at Mānoa
Honolulu, HI 96822
ABSTRACT
Knowledge about the Moon’s geology has been acquired through NASA’s lunar satellites
and Apollo landings. However, the geology of the lunar poles is not well understood. The goal
of this research was to investigate the surface geology of the north pole of the Moon using new
remote sensing data sets. Data from Lunar Orbiter Laser Altimeter (LOLA) and Mini-RF
Technology Demonstration were used to search for previously unidentified mare material. One
mare deposit, about 23 km in length, was discovered based on its data characteristics in LOLA
reflectance, Mini-RF, and a LOLA Digital Elevation Model. KAGUYA Spectral Profiler data
were used to assess the mineralogical composition at the pole. Maps of the mineralogical
composition for olivine, plagioclase, clinopyroxene, and orthopyroxene were assembled from the
Spectral Profiler data. This research demonstrates the advantages of new remote sensing data
sets, including those that do not depend on light, to investigate the geology at the Moon’s poles.
The findings of this investigation and future studies may identify a future landing site and
resources at the poles that may be available to future astronauts landing on the Moon.
INTRODUCTION
We investigated the surface geology of the north pole of the Moon, assessing the
mineralogical composition for the four major lunar minerals and searching for previously
unidentified mare deposits using new remote sensing data from NASA and JAXA instruments.
The lunar poles are the last regions of the Moon without explicitly understood geology
and composition. Rock and soil samples brought back from the Apollo missions taught us about
the geology and composition of the lunar surface; however, samples from the lunar poles have
never been obtained because all of the Apollo and Luna sample return missions landed far from
the poles. Our knowledge of lunar geology depends upon interpretation of remote sensing data.
Until very recently, limitations of previous remote sensing data hindered our understanding of
the lunar poles. At the poles the Sun only rises a small angle above the horizon, resulting in very
low sun angles that make subtle surface features difficult to identify because differences in
brightness are difficult to detect. In addition, the ability to interpret images was limited because
of poor image resolution. We hypothesize that there are volcanic deposits at the Moon’s north
pole that have not been identified because of the limitations of previous remote sensing data sets.
Furthermore, because previous remote sensing data sets have not been successfully used to
characterize the mineralogy at the lunar poles, we aim to assess the mineralogical composition
for the four major lunar minerals at the lunar north pole.
New remote sensing data provide a means to investigate the surface geology at the
Moon’s poles. NASA’s Lunar Reconnaissance Orbiter (LRO) overcomes limitations of previous
34
remote sensing data sets and provides several useful means of analyzing lunar geology. We used
data from LRO’s Lunar Orbiter Laser Altimeter (LOLA) and the Mini-RF Technology
Demonstration, which do not depend on sunlight, solving the polar lighting problem. LOLA
measures surface reflectance and topography using lasers that illuminate the lunar surface. The
Mini-RF Technology Demonstration uses radar to measure surface roughness. Together the data
sets provide measurements of surface roughness, elevation, and reflectance, which can be used to
identify volcanic materials. At the University of Hawai‘i at Mānoa, Dr. Gillis-Davis has used
Mini-RF to investigate both pyroclastic deposits and TiO2 content (Carter et al., 2010; GillisDavis et al., 2010). LOLA reflectance measurements have been used to search for water at the
poles (Zuber et al., 2012). In our investigation, data from Mini-RF and LOLA were used to
search for previously unidentified mare material (Fig. 1).
Figure 1: New remote sensing data sets used to search for previously unidentified mare material. Maps
from 70°N to the north pole, from left to right: LOLA reflectance, Mini-RF, and LOLA Digital Elevation
Model. (Bussey et al., 2008; Smith et al., 2006).
In addition to the LRO data, we used data from the Japan Aerospace Exploration’s
Agency’s (JAXA) KAGUYA Spectral Profiler. The reflectance spectra in visible and near
infrared were used to characterize the mineralogy of the lit portion of the pole. We assessed the
mineralogical composition for the four major lunar minerals: olivine, plagioclase, clinopyroxene,
and orthopyroxene.
METHODS
For this investigation, the lunar north pole was examined from 70°N to the pole. Mini-RF
and LOLA data were obtained from NASA. A Mini-RF map and a LOLA Digital Elevation
Model (DEM) were provided as polar stereographic projections. My mentor, Dr. Paul Lucey,
obtained KAGUYA Spectral Profiler data from JAXA and processed the data to a polar
stereographic projection. My mentor and I processed LOLA reflectance data using Interactive
Data Language (IDL) in order to make a polar stereographic projection.
In order to search for previously unidentified mare material, volcanic terrains previously
mapped by NASA were examined (Fig. 2). The identified volcanic deposits were used as a
training tool to develop criteria to identify any new deposits that might be revealed by the new
data. I became familiar with LOLA and Mini-RF characteristics of known volcanic terrains on
the Moon. The study area was then examined in Mini-RF, LOLA reflectance, and LOLA DEM
maps for areas that matched the characteristics established of the known volcanic deposits.
35
Figure 2: Geologic map of the Moon’s north pole from 45°N to the pole, prepared by NASA. Our study
area from 70°N to the pole is shown in the black circle. The inset map shows two previously identified
maria (bright red inside the black circle). The maria were used as a training tool to become familiar with
their characteristics in each of the data sets. (Lucchitta, 1978).
Because the KAGUYA Spectral Profiler uses the Sun for its light source, the problem of
extreme lighting conditions affects this data set. Crater walls and topographic highs that face the
low polar Sun in principle have enough lighting to collect quality data. To make the maps of the
mineralogical composition, we first went through the Spectral Profiler polar data using IDL and
attempted to isolate the regions with highest signal, which are the brightest portions of the polar
data. We then applied Dr. Lucey’s mineral mapping program to those data.
RESULTS
I examined two maria in my study area that were previously mapped by the NASA
(Fig. 2). The maria are extremely dark in LOLA reflectance measurements (Fig. 3). Because
maria have relatively smooth surfaces, they are relatively dark in Mini-RF (Fig. 4). In addition,
the maria are characterized in the LOLA DEM as areas lower than the surroundings and uniform
in elevation, because lava fills in flat areas of low elevation forming a surface with uniform
elevation (Fig. 5).
36
Figure 3: Mare material appears extremely dark in LOLA reflectance measurements.
Figure 4: Mare material appears relatively dark in Mini-RF measurements.
Figure 5: Mare material is characterized in the LOLA DEM as an area lower than the surroundings and
uniform in elevation.
37
Based on the data characteristics of the two previously mapped maria, I was able to
identify one new mare deposit in the polar region (Fig. 6). The mare is approximately 23 km in
length and was previously mapped as lineated basin material by NASA. The newly discovered
mare meets all of the criteria established by looking at previously identified maria. It is
extremely dark in LOLA reflectance. In addition, the mare is relatively dark in Mini-RF,
meaning it is a smooth surface. In the LOLA DEM, it is a flat area of low elevation. This was
the only feature in my study area that met all of these criteria in each data set.
Figure 6: This mare deposit, approximately 23 km in length, was previously mapped by NASA as
lineated basin material. New remote sensing data, including (from left to right) LOLA reflectance,
Mini-RF, and LOLA DEM, allowed for the discovery of this mare. The red box is centered on the
mare deposit in each image.
Maps of the mineralogical composition at the north pole for olivine, plagioclase,
clinopyroxene, and orthopyroxene were assembled from data from KAGUYA Spectral Profiler
(Fig. 7). This portion of the project was less successful, but shows promise. The problems with
conventional imaging systems described above, in particular the extreme lighting conditions,
also holds for spectroscopic instruments that use the Sun for their light source. However, even at
the poles crater walls and other topographic highs that face the low polar Sun in principle have
enough lighting to collect quality data. We went through the polar data and attempted to isolate
the regions with highest signal (the brightest portions of the polar data) and applied Dr. Lucey’s
mineral mapping program to those data. Unfortunately, our attempt was apparently not
successful, as the polar mineral images show no interpretable features. The concept seems worth
pursuing and Dr. Lucey will continue to work on this new method for polar analysis.
38
Figure 7: Maps of mineralogical composition from 70°N to the north pole. Clockwise from top left:
clinopyroxene, orthopyroxene, olivine, and plagioclase. Brighter areas have a greater composition of a
given mineral than darker areas.
DISCUSSION AND FUTURE RESEARCH
This research demonstrates the advantages of new remote sensing data sets to investigate
the geology at the Moon’s poles. Combining different data sets that do not depend on light
allows us to search for volcanic deposits. The Mini-RF map and the LOLA reflectance map and
DEM were successfully used to find a mare that was never previously identified. Besides the
maria used as a training tool in the investigation, the mare that we discovered is the only other
feature that is extremely dark in the LOLA reflectance map. Thus, we believe that LOLA
reflectance data are a critical tool for finding unidentified mare material.
Mini-RF is also a useful tool for identifying maria. Both the previously identified and the
newly discovered maria appeared dark gray. However, in both cases there was a brighter feature
within the deposit. We believe that the brighter features are due to rougher material, such as
ejecta material, covering the surface of the maria. The LOLA DEM also suggests that part of the
maria is covered, because the area of similar elevation is much larger than the size of the maria
seen in other data sets. Because the Mini-RF shows both dark and bright features characterizing
the maria, we must be careful using this data set to identify maria. Thus, it is important to use
other data sets alongside radar data when searching for mare material.
The LOLA Digital Elevation Model was useful as a final tool to verify that a possible
mare deposit was in an area of low elevation. Maria occur in areas lower in elevation than the
surroundings, because lava fills in topographic depressions. In addition, maria occur where the
39
topography is relatively flat. Thus, mare material is characterized in the LOLA DEM as areas
that are lower than the surroundings and do not vary in elevation. If an area that I was examining
as a possible mare was brighter than the surrounding, it could be ruled out as a mare candidate.
Although we were not successful in determining the mineralogical composition at the
north pole using KAGUYA Spectral Profiler data, the concept seems worth pursuing. Within the
time frame of this project, it was not possible to attempt to improve the mineral images.
However, Dr. Lucey will continue to work on this new method for polar analysis.
With the time constraints of this project, it was only possible to investigate the Moon’s
north pole. We believe that a similar investigation of the Moon’s south pole should be
conducted in the future. It is possible that the south pole also contains maria that were never
identified because of limitations in previous remote sensing data. In addition, the south pole’s
mineralogical composition should be assessed after further development of our methods.
CONCLUSION
New remote sensing data sets overcome the limitations of previous remote sensing data
sets and provide a means to investigate the geology at the lunar poles. Data from NASA’s Lunar
Orbiter Laser Altimeter and Mini-RF Technology Demonstration were used to discover an
unknown mare deposit. JAXA’s KAGUYA Spectral Profiler allowed us to develop methods that
may be used in the future to characterize the mineralogical composition of the Moon’s north
pole. This research is relevant to NASA’s goals, because the findings of this investigation and
future studies may identify a future landing site and resources that may be available to future
astronauts landing on the Moon.
ACKNOWLEDGEMENTS
I would like to thank the NASA Space Grant Consortium at the University of Hawai‘i at
Mānoa for providing me with the opportunity to conduct research in planetary geology. I would
also like to thank Dr. Paul Lucey for taking the time to teach me about lunar geology, remote
sensing, and IDL. Thanks are also owed to Dr. Edward Scott for sparking my interest in the field
and for encouraging me to apply for the fellowship. My experience during the fellowship
inspired me to pursue a graduate degree in planetary geology.
40
REFERENCES
Bussey, D., Carter, L., Spudis, P., Nozette, S., Lichtenberg, C., Raney, R., Marinelli, W.,
Winters, H., and Mini-RF Science Team (2008) Mini-RF: Imaging radars for exploring
the Moon. Proceedings Lunar and Planetary Institute Science Conference, LPI
Contribution no. 1415, abstract no. 2083.
Carter, L., Gillis-Davis, J., Bussey, D., Spudis, P., Neish, C., Thompson, B., Patterson, G., and
Raney, R. (2010) Mini-RF observations of a sample of large lunar pyroclastic deposits.
Proceedings Lunar and Planetary Institute Science Conference, LPI Contribution no.
1533, 1563.
Gillis-Davis, J., Bussey, B., Trang, D., Carter, L., and Williams, K. (2010) Using Mini-RF to
improve accuracy of lunar TiO2 maps, Proceedings AGU Fall Meeting Abstracts 1,
abstract no. P23A-1612.
Lucchitta, B. K. (1978) Geologic map of the north side of the Moon, 1:5,000,000. In: Geologic
Atlas of the Moon, North Side of the Moon. Reston: Department of the Interior−United
States Geologic Survey, I-1062.
Smith, D., Zuber, M., Neumann, G., Lemoine, F., Robinson, M., Aharonson, O., Head, J., Sun,
X., Cavanaugh, J., and Jackson, G. (2006) The lunar orbiter laser altimeter (LOLA) on
the lunar reconnaissance orbiter, Proceedings AGU Fall Meeting Abstracts 1, abstract no.
U41C-0826.
Zuber, M. T., Head, J. W., Smith, D. E., Neumann, G. A., Mazarico, E., Torrence, M. H.,
Aharonson, O., Tye, A. R., Fassett, C. I., and Rosenburg, M. A. (2012) Constraints on the
volatile distribution within Shackleton crater at the lunar south pole. Nature 486, 378381.
41