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| Titel |
Estimated Rock Abundance and Thermophysical Parameters in Oppenheimer Crater on the Moon |
| VerfasserIn |
Karin E. Bauch, Harald Hiesinger, Mikhail Ivanov, Carolyn H. van der Bogert, Jan-Hendrik Pasckert, Julia Weinauer |
| Konferenz |
EGU General Assembly 2016
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 18 (2016) |
| Datensatznummer |
250135628
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| Publikation (Nr.) |
 EGU/EGU2016-16516.pdf |
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| Zusammenfassung |
| Oppenheimer crater is located in the north-east of the South Pole-Aitken basin (SPA), the
largest impact structure on the Moon [e.g., 1]. The crater is ∼215km in diameter and has an
estimated age of ∼4.1 Ga [2]. The floor of Oppenheimer shows evidence of dark mantling
deposits and a concentric system of graben structures close to the rim of the crater [3]. Image
and topography data show that the floor is flat apart from the graben structures and
subsequent impacts on the floor. Oppenheimer-U (∼40km) and -H (∼35km) are
floor-fractured craters within the north-west and south-east portions of Oppenheimer crater
[3].
Dark mantling deposits on the floor are associated with the graben system. [3] estimated
an age between ∼3.98Ga and ∼3.66Ga for the pyroclastic activity, based on crater
size-frequency distribution (CSFD) measurements on Lunar Reconnaissance Orbiter (LRO)
WAC and NAC images.
In this study we compare the mapping results of [3] with temperature data of the LRO
Diviner experiment [4] using a numerical model [5, 6]. Nighttime temperature variations are
directly influenced by the surface and subsurface thermophysical properties, namely bulk
density, heat capacity, and thermal conductivity [7, 8]. These properties can be summarized to
a thermal inertia, which represents the ability to conduct and store heat [8]. Low
thermal inertia units, such as dust and other fine grained material, quickly respond to
temperature changes, which results in large temperature amplitudes between the lunar day
and night. On the other hand, high thermal inertia material, e.g. rocks or bedrock,
take more time to heat up during the day and reradiate the heat during the night
[8].
Relative rock abundances are derived from temperature measurements of the same
location at different wavelengths. Brightness temperatures are a function of wavelength and
increase with decreasing wavelength [9, 10]. This nonlinearity of the Planck radiance can be
used to determine the amount of anisothermal surfaces and, thus, the abundance of rocks
within a field of view [e.g., 6, 9, 10].
The thermal maps show low temperatures, thus low thermal inertia and low rock
abundances on the flat floor of Oppenheimer. Dark mantle deposits have similar thermal
signatures as the floor. Higher rock abundances and thermal inertias are associated with the
graben structures close to the rim of Oppenheimer and the floors of Oppenheimer-U and -H.
We found that the highest values correlate with fresh craters in the northern part of
Oppenheimer. High-resolution NAC images confirm the presence of boulders on the
surface.
References: [1] Petro, N.E., Pieters, C. M. (2004), JGR 109, E6. [2] Hiesinger, H. et al.
(2012), LPSC XLIII, #2863. [3] Ivanov, M. et al. (2015), LPSC IIIX, #1070. [4] Paige, D. et
al. (2010), Spac. Sci. Rev. 150, Num 1-4, p125-160. [5] Bauch, K.E. et al. (2014), PSS 101,
27-36. [6] Bauch, K.E. at al. (2013), EGU2013-8053. [7] Urquhart, M.L. and Jakosky, B.M.
(1997), JGR 102, 10,959-10,969. [8] Mellon, M.T. et al. (2000), Icarus 148, 437-455. [9]
Christensen, P.R. (1986), Icarus 68, 217-238. [10] Bandfield, J.L. et al. (2011), JGR 108,
E12, 8086. |
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