The Curie mission would constrain the existence of the putative cataclysm by determining the age of samples directly sourced from the impact melt sheet of a major pre-Imbrium lunar basin. The measurements would also enable further understanding of lunar evolution by characterizing new lunar lithologies far from the Apollo and Luna landing sites, including the very low-Ti basalts in Mare Crisium and potential olivine rich lithologies in the margins of both Mare Nectaris and Mars Crisium. Equipped with a mass spectrometer and a LIBS, Curie would also be well-placed to survey volatile components of the lunar regolith, including surface-bound hydrogen

Clegg, S. M.

Cohen, B. A.

Denevi, B. W.

Dyar, M. E.

Elardo, S. M.

Grinspoon, D. H.

Hiesinger, H.

Lawrence, S. J.

Liu, Y.

McCanta, M. C.

Moriarty, D. P.

Norman, M. D.

Petro, N. E.

Runyon, K. D.

Schwenzer, S. P.

Swindle, T. D.

van der Bogart, C. H.

Wiens, R. C.

English

Open Research Online (The Open University)

Open Research OnlineThe Open University’s repository of research publicationsand other research outputsCurie: Constraining Solar System Bombardment UsingIn Situ Radiometric DatingConference or Workshop ItemHow to cite:Cohen, B. A.; Petro, N. E.; Lawrence, S. J.; Clegg, S. M.; Denevi, B. W.; Dyar, M. E.; Elardo, S. M.;Grinspoon, D. H.; Hiesinger, H.; Liu, Y.; McCanta, M. C.; Moriarty, D. P.; Norman, M. D.; Runyon, K. D.; Schwenzer,S. P.; Swindle, T. D.; van der Bogart, C. H. and Wiens, R. C. (2018). Curie: Constraining Solar System BombardmentUsing In Situ Radiometric Dating. In: 49th Lunar and Planetary Science Conference, 19-23 Mar 2018, The Woodlands,Houston, Texas, USA.For guidance on citations see FAQs.c© [not recorded]Version: Version of RecordLink(s) to article on publisher’s website:https://www.hou.usra.edu/meetings/lpsc2018/pdf/1029.pdfCopyright and Moral Rights for the articles on this site are retained by the individual authors and/or other copyrightowners. For more information on Open Research Online’s data policy on reuse of materials please consult the policiespage.oro.open.ac.ukCURIE: CONSTRAINING SOLAR SYSTEM BOMBARDMENT USING IN SITU RADIOMETRIC DATING.  B. A. Cohen1, N. E. Petro1, S. J. Lawrence2, S. M. Clegg3, B. W. Denevi4, M. E. Dyar5, S. M. Elardo6, D. H. Grinspoon5, H. Hiesinger7, Y. Liu8, M. C. McCanta9, D. P. Moriarty1, M. D. Norman10, K. D. Runyon4, S. P. Schwenzer11, T. D. Swindle12, C. H. van der Bogert7, and R. C. Wiens13. 1NASA Goddard Space Flight Center (bar-bara.a.cohen@nasa.gov), 2NASA Lyndon B. Johnson Space Center, 3Los Alamos National Laboratory, 4JHU Ap-plied Physics Laboratory, 5Planetary Science Institute, 6Carnegie Institution of Washington, 7Westfälische Wil-helms-Universität Münster, 8Jet Propulsion Laboratory, 9University of Tennessee, 10Australian National University, 11Open University, 13University of Arizona.  Introduction: Establishing an absolute lunar chro-nology has important ramifications for understanding the early structure of the Solar System and the dynam-ical evolution and composition of planetary bodies. The age distribution of lunar impact breccias inspired the idea of a catastrophic influx of asteroids and/or comets about 4 billion years ago and motivated new models of planetary dynamics. The dynamical models to explain such a phenomenon encompass the gas-dust dynamics of forming disks and giant planet migration; these models are now invoked to understand not only our Solar System, but exoplanets around other stars. This event would also have affected the Earth at a time when other evidence shows that continents, oceans, and perhaps even life already existed.  Linking lunar samples to specific basins underpins the concept of a putative lunar cataclysm. Until recent-ly there was a broad consensus among lunar geologists about the relationships of samples collected by the Apollo missions to the Imbrium (Apollo 14), Serenita-tis (Apollo 17), and Nectaris (Apollo 16) basins [1]. Today, most of these relationships have been ques-tioned and are under active debate. The best available age for Imbrium appears to be 3.92 ± 0.01 Ga from KREEP-rich breccias and melt rocks collected at the Apollo 12 and 14 sites [2-5]. Analysis of LRO images of boulder tracks verified that the boulders sampled at the Apollo 17 site originated in outcrops within the North Massif walls, which had been interpreted as Se-renitatis ejecta [6, 7]. However, the overlying Sculp-tured Hills deposits may be more closely related to Imbrium than Serenitatis [8, 9]. U-Pb dating of Ca-phosphates in Apollo 17 melt breccias appears to sup-port an Imbrium origin for these rocks, while the Ar distribution is less straightforward [10, 11]. The alumi-nous Descartes breccias from Apollo 16, which have been interpreted as either Imbrum or Nectaris ejecta, range in age from 3.9 to 4.1 Ga, leading to a proposed old age for Nectaris [12, 13]. However, subsequent studies showed that the youngest population of clasts in these breccias is coeval with the KREEP-rich, crys-talline melt rocks that are the best candidates for Im-brium ejecta, supporting geological observations that favor emplacement of the Descartes breccias as Imbri-um ejecta [14]. Luna 20 fragments interpreted to be Crisium impact melt have radiometric ages ranging from ~3.84 Ga to 3.895 Ga [15-17]. Updated Apollo 17 sample ages, also interpreted as representing Crisium impact-melt rocks, range from 3.88 to 3.93 Ga [7]. The crater density data for Crisium ejecta similarly vary in their model ages from 3.99 Ga to 3.94 Ga [18, 19]. It is clear that there is little consensus on what samples represent impact melt from basins other than Imbrium, reopening the pre-Imbrian impact history to debate. The Decadal Survey twice recognized the im-portance of understanding the lunar cataclysm by rec-ommending sample return from the South Pole-Aitken (SPA) basin, which would enable high-precision measurements by laboratory methods to resolve sam-ple petrology and ages. However, if an SPA sample-return mission is not selected, it may be possible to understand the formation age of a nearside basin using in situ dating in a Discovery-class package. We are currently developing Curie, a potential Discovery mis-sion concept that would directly constrain the onset of the cataclysm by new in situ dating of Nectaris or Crisium – both stratigraphically critical lunar basins. Although the Nectaris and Crisium basins have ex-perienced both basaltic infill and erosion, their original multiring morphologies are still recognizable. Updated geologic maps of the Nectaris basin and its surround-ing terrain have identified small plains near inner-basin ring massifs and inter-massif “draped” deposits as pos-sible remnants of the Nectaris basin impact melt sheet [20, 21]. Similar efforts also identified kipukas of the Crisium basin impact melt sheet, based on their mor-phology and composition [22]. In both Nectaris and Crisium, these exposures occur between the inner and outer basin rings and exhibit cracked and fissured morphologies consistent with those at both fresh cra-ters (e.g., Tycho and King craters [23]) and older im-pact melts (e.g., Orientale [24, 25]), as well as embay-ment by subsequent mare basalt flows. The composi-tion of these areas is less mafic than the surrounding basalts, a reflection of the lunar highlands target mate-rials. If these are indeed areas of preserved Nectaris or Crisium impact melt, such sites would be unique among basins as in situ impact melt exposures.  In contrast to attempts to identify impact melt rocks ejected from the basin to distant sites like Apollo 17 or Luna 20, regolith formed atop an impact melt substrate should contain a majority of impact-melt rocks – simi-lar to the dominance of basaltic materials in the rego-lith developed over Mare Tranquilitatis at Apollo 11 [26, 27]. There is no KREEP-rich compositional halo 1029.pdf49th Lunar and Planetary Science Conference 2018 (LPI Contrib. No. 2083)around Nectaris or Crisium, so their impact-melt de-posits should be aluminous and possibly slightly iron-rich [17, 28]. Such samples would be readily distin-guished from KREEPy Imbrium and basaltic mare materials, though multiple measurements of impact-melt candidate rocks would be required to provide con-fidence in both the origin and age of an impact-melt lithology. Assessing the onset of a putative lunar cataclysm using the age of the Nectaris or Crisium basins requires only coarse precision. If the measured basin age were ~3.9 Ga (as suggested for Crisium), it would lend cre-dence to at least a terminal cataclysm, with Crisium and Imbrium as large impact events occurring closely spaced in time significantly later than solar system formation. If the measured basin age were ~4.1 Ga (as suggested for Nectaris), a more expansive epoch of bombardment would be allowable for the nearside ba-sins, with significant periods of time occurring be-tween basin-forming events. If either basin proved even older, there may have been no unusual spike in flux but rather a declining rate of bombardment over time. These intervals can be recognized with ages ±100 Myr (or less), currently achievable with in situ tech-niques [29-31].  A stationary lander could retrieve small rock sam-ples from the regolith, using technologies similar to that developed for the proposed MoonRise mission [13]. Samples of interest would be dated using K-Ar techniques using LIBS to measure the K abundance and to release noble gases; mass spectrometry to measure the evolved Ar, and optical measurement of the ablated volume. These components would provide essential measurements to understand the origin and evolution of the samples (complete elemental abun-dance, evolved volatile analysis, microimaging) as well as in situ geochronology [29].  The Curie mission would constrain the existence of the putative cataclysm by determining the age of sam-ples directly sourced from the impact melt sheet of a major pre-Imbrium lunar basin. The measurements would also enable further understanding of lunar evo-lution by characterizing new lunar lithologies far from the Apollo and Luna landing sites, including the very-low-Ti basalts in Mare Crisium and potential olivine-rich lithologies in the margins of both Mare Nectaris and Mars Crisium [32]. Equipped with a mass spec-trometer and a LIBS, Curie would also be well-placed to survey volatile components of the lunar regolith, including surface-bound hydrogen [33,34].  References: [1] Sto ̈ffler, D., et al. (2006) Reviews in Mineralogy and Geochemistry 60, 519-596. [2] Nemchin, A., et al. (2009) Nature Geoscience 2, 133-136. [3] Liu, D., et al. (2012) Earth Planet. Sci. Lett. 319-320, 277-286. [4] Snape, J.F., et al. (2016) Geo-chim. Cosmochim. Acta 174, 13-29. [5] Merle, R.E., et al. (2017) Met. Planet. Sci. 52, 842-858. [6] Hurwitz, D. and D.A. Kring (2016) Earth Planet. Sci. Lett. 436, 64-70. [7] Schmitt, H.H., et al. (2017) Icarus 298, 2-33. [8] Spudis, P.D., et al. (2011) J. Geophys. Res. 116. [9] Fassett, C.I., et al. (2012) J. Geophys. Res. 117. [10] Thiessen, F., et al. (2017) Met. Planet. Sci. 52, 584-611. [11] Mercer, C.M., et al. (2015) Science Advanc-es 1. [12] James, O.B. (1981) Proc. Lunar Planet. Sci. Conf. 12, 209-233. [13] Fernandes, V.A., et al. (2013) Met. Planet. Sci. 48, 241-269. [14] Norman, M.D., et al. (2010) Geochim. Cosmochim. Acta 74, 763-783. [15] Cadogan, P.H. and G. Turner (1977) Philosophi-cal Transactions of the Royal Society of London A284, 167-177. [16] Stettler, A. and F. Albarede (1978) Earth Planet. Sci. Lett. 38, 401-406. [17] Swindle, T.D., et al. (1991) Proc. Lunar Planet. Sci. Conf. 21, 167-181. [18] Neukum, G.P., (1983) Tenure Thesis, Ludwig-Maximilians Universität. [19] van der Bogert, C.H., et al. (2018) LPSC 49, #1028. [20] Spudis, P.D. and M.C. Smith (2013) Lunar Planet. Sci. Conf., #1483. [21] Smith, M.C. and P.D. Spudis (2013) Lunar Planet. Sci. Conf., #1248. [22] Spudis, P.D. and M.U. Sliz (2017) Geophys. Res. Lett. 44, 1260-1265. [23] Howard, K.A. and H.G. Wilshire (1975) U S Geological Survey Journal Research 3, 237-251. [24] Spudis, P.D., et al. (2014) J. Geophys. Res. Planets 119, 19-29. [25] Wil-helms, D.E. (1987) U.S. Geological Survey Profes-sional Paper 1348. [26] Haskin, L.A., et al. (2003) Met. Planet. Sci. 38, 13-34. [27] Petro, N.E. and C.M. Pieters (2004) J. Geophys. Res. Planets 109, doi 10.1029/2003JE002182. [28] Spudis, P.D. (1984) J. Geophys. Res. 89, C95-C107. [29] Cohen, B.A., et al. (2014) Geost Geoanal Res. 38(4), 421-439. [30] Cho, Y., et al. (2016) Planet Space Sci 128, 14-29. [31] De-vismes, D., et al. (2016) Geost Geoanal Res. DOI: 10.1111/ggr.12118. [32] Corley, L. M., et al. (2017) Icarus 300, 287–304 [33] Schröder, S., et al. (2015) Icarus 249, 43-61. [34] Meslin, P.Y., et al. (2013) Sci-ence 341.      1029.pdf49th Lunar and Planetary Science Conference 2018 (LPI Contrib. No. 2083)

Curie: Constraining Solar System Bombardment Using In Situ Radiometric Dating

Curie: Constraining Solar System Bombardment Using In Situ Radiometric Dating

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