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Impact Ejection of Lunar Meteorites and the Age of Giordano Bruno ⇑ Jörg Fritz

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Impact Ejection of Lunar Meteorites and the Age of Giordano Bruno ⇑ Jörg Fritz Icarus 221 (2012) 1183–1186 Contents lists available at SciVerse ScienceDirect Icarus journal homepage: www.elsevier.com/locate/icarus Note Impact ejection of lunar meteorites and the age of Giordano Bruno ⇑ Jörg Fritz Museum für Naturkunde, Invalidenstrasse 43, 10115 Berlin, Germany article info abstract Article history: Based on literature data from lunar meteorites and orbital observations it is argued that the lunar crater Giordano Received 25 April 2012 Bruno (22 km £) formed more than 1 Ma ago and probably ejected the lunar meteorites Yamato 82192/82193/ 3 Revised 17 August 2012 86032 at 8.5 ± 1.5 Ma ago from the Th-poor highlands of the Moon. The efficiency and time scale to deliver He-rich Accepted 18 August 2012 lunar material into Earth’s sediments is discussed to assess the temporal relationship between the Giordano Bruno cra- 3 Available online 30 August 2012 tering event and a 1 Ma enduring He-spike which is observed in 8.2 Ma old sediments on Earth. Ó 2012 Elsevier Inc. All rights reserved. Keywords: Earth Cratering Moon Meteorites 1. Introduction 3. Number and size of lunar impact ejection events The rapidly increasing number of lunar and martian meteorites recovered in hot Impact ejection and the interplanetary transfer of rock fragments is docu- and cold deserts has revolutionized our understanding of the impact-related trans- mented by 104 martian and 154 lunar meteorites with individual names (Meteor- fer of solid rock fragments between planets in the same Solar System (Gladman itical Bulletin Data Base 14. March 2012; http://www.lpi.usra.edu/meteor/ et al., 1995; Artemieva and Ivanov, 2004; Fritz et al., 2005; Artemieva and Shuvalov, metbull.php). Some of these meteorites were ejected together from the Moon 2008). The suite of available lunar and martian meteorites provide unique samples (launch paired) or are fragments of a single meteoroid that disrupted during atmo- to investigate the recent impact record of these planets, because absolute ages of spheric entry (fall paired). Launch and fall pairing is disentangled on the basis of the ejection events can be deduced from the cosmic ray exposure history (i.e., Nish- petrology and cosmic ray exposure history (Table 1 and Fig. 1). The ejection age iizumi et al., 1991; Eugster et al., 2002). Petrology, geochemistry, and the timescales is the sum of the cosmic ray exposure during space transit (4p small body) plus of delivery and recovery of lunar meteorites are compared with remote sensing data the terrestrial residence time. These ages are (besides problems due to complex regarding the lunar impact record of the last 100 Ma to help identify potential exposure histories) determined by cosmogenic nuclide abundances (Nishiizumi source craters. Here I discuss the age of the lunar crater Giordano Bruno, with impli- et al., 1991; Eugster et al., 2002). cations for recovering its ejecta as lunar meteorites, and for the extraterrestrial 3He Based on ejection ages and petrology, the suite of martian meteorites derives preserved in Earth’s sedimentary record. from 7 different impact events and each delivered similar lithologies during the last 20 Ma (Christen et al., 2005; Fritz et al., 2007a). Disentangling launch and fall pairing for lunar meteorites is less obvious. The impact gardened lunar surface is 2. Observations of the Giordano Bruno crater covered with regolith composed of a petrologically diverse mixture of rock to dust sized fragments with complex cosmic ray exposure (CRE) histories. The petrologic A22km£ crater just beyond the north-eastern limb of the Moon (36°N, 103°E) diversity of lunar meteorites has been used to propose 30–50 different ejection is named after an Italian priest, philosopher and astronomer. Giordano Bruno events (Korotev et al., 2009). The CRE age distribution document at least eight dif- (1548–1600 AD) expanded the helio-centric view of Copernicus by considering that ferent events (Lorenzetti et al., 2005; Fig. 1). the universe is infinite, that our Sun is a star like other star, and that these other The size of these impact events is constrained by the temporal frequency of the stars host planetary systems populated by intelligent beings (Bruno, 1584). documented ejection events and the lunar crater production rates (and scaled for The Giordano Bruno crater displays a well preserved ray system (Whitaker, Mars). It follows that projectiles as small as 30 m and 200 m can produce lunar 1963). This impact structure is, according to the low spectral maturity level of and martian meteorites, respectively, and the resulting craters are small in size (1 the ejecta blanket (Pieters et al., 1994), the youngest lunar crater >20 km £ (Grier and 3km£ on Moon and Mars, respectively; Artemieva and Ivanov, 2004; Fritz et al., 2001). Hartung (1976) proposed that the Giordano Bruno forming impact was et al., 2007a). Based upon surface ages from crater counting, only four lunar craters eye witnessed by medieval monks on June 18th, 1178 AD Calame and Mulholland >20 km £ formed during the last 100 Ma on the Moon (Morota et al., 2009; Grier (1978) determined that formation in medieval times would have coincided with et al., 2001). the large amplitudes of the free liberation of the Moon. Using Kaguya orbiter data, Plescia et al. (2011) consider a historical age for this crater probable. However, the ejecta blanket of Giordano Bruno shows a 1–10 Ma crater retention age (Morota 4. Total mass of lunar ejecta delivered to Earth et al., 2009), which appears consistent with detailed observations using Lunar Reconnaissance Orbiter images (Shkuratov et al., 2012). The total mass of lunar ejecta delivered to the Earth’s upper atmosphere varies from between 0.25 and 2 of the total mass projectiles impacting the Moon (Glad- man et al., 1995; Fritz et al., 2007b; Artemieva and Shuvalov, 2008) and may equa- ⇑ Fax: +49 30 2093 8565. ted to 1 for simplicity. Using the lunar size–frequency distribution (Neukum, 1983) E-mail address: [email protected]. I estimate 6.2 Â 109 and 1.8 Â 1012 kg of lunar ejecta arriving on Earth’s atmosphere 0019-1035/$ - see front matter Ó 2012 Elsevier Inc. All rights reserved. doi:10.1016/j.icarus.2012.08.019 1184 J. Fritz / Icarus 221 (2012) 1183–1186 Table 1 Compilation of literature data for lunar meteorites: Tspace = irradiation time as a small body in space, Tterr = subsequent time interval the meteorite resided on Earth and was shielded by the atmosphere from cosmic rays; Teject = Tspace + Tterr, the time at which the rock was impact ejected from the Moon. All ages are given in million years [Ma]. Thorium [Th] elemental abundance of the meteorite in [ppm]. References [Ref.] for cosmic ray exposure data: (1) Nishiizumi and Caffee (2001b); (2) Nishiizumi et al. (2004); (3) Nishiizumi et al. (2006); (4) Serefiddin et al. (2011); (5) Nishiizumi and Caffee (2001a); (6) Scherer et al. (1998); (7) Nishiizumi et al. (1998); (8) Bartoschewitz et al. (2009); (9) Nishiizumi et al. (2009); (10) Nishiizumi et al. (1991); (11) Nishiizumi and Caffee (2006); (12) Nishiizumi et al. (1988); (13) Eugster (1988); (14) Lorenzetti et al. (2005); (15) Nyquist et al. (2006); (16) Nishiizumi et al. (1996); (17) Thalmann et al. (1996); (108) Nishiizumi et al. (2005); (19) Vogt et al. (1993); (20) Nishiizumi et al. (1999); (21) Nishiizumi and Caffee (1996); and (22) Gnos et al. (2004). Data for Th-concentrations from (A) Korotev (2005); (B) Korotev et al. (2003); and (C) Korotev et al. (2008). Name Tspace Tterr Teject Th Ref. Thorium-poor feldspatic breccias Dhofar 025 >5 0.55 ± 0.05 13–20 0.5 1; A Dhofar 026 <0.005 0.4 1; B Dhofar 081/280/910 <0.01 0.04 ± 0.02 0.04 ± 0.02 0.2 2; 3; B 0.23 0.22 0.4 4 Dhofar 489/908/911/1085 0.004 ± 0.001 0.3 0.3 ± 0.1 0.07 3; A Dhofar 1084 0.32 ± 0.06 0.4 5; C DaG 262 0.5 0.3 0.4 7; B DaG 400 1 0.4 6; B SaU 300 <0.2 0.1 ± 0.1 0.5 8; 4 NWA 482 0.9 ± 0.2 0.09 ± 0.03 0.99 ± 0.23 0.2 5; B NWA 5000 >0.0013 <0.01 0.7 9; C NEA 001 0.44 ± 0.08 0.3 3; A ALHA81005 <0.05 0.04 ± 0.01 0.04 ± 0.01 0.3 10; B MAC 88104/88105 0.045 ± 0.005 0.23 ± 0.02 0.27 ± 0.025 0.4 10; B 0.04 0.14 0.18 4 PCA 02007 0.95 ± 0.11 <0.03 0.95 ± 0.14 0.4 11; A Y-82192/82193/86032 5–11 0.077 ± 0.005 8 ± 3 0.19 12;13;14 8.5 ± 1.5 15; B Y-791197 <0.002 0.06 ± 0.03 0.06 ± 0.03 0.3 10; B QUE 93069/94269 0.035 ± 0.015 0.0075 ± 0.0025 0.04 ± 0.02 0.5 16; B 0.15 ± 0.02 <0.015 0.16 ± 0.03 17 Mingled breccias Calcalong Creek 3 ± 1 <0.03 3 ± 1 4 16; B Kalahari 008/009 0.00023 ± 0.00009 0.4 ± 0.1 0.4 ± 0.1 0.2 18; C EET 87521/96008 <0.1 0.8 ± 0.3 0.85 ± 0.35 0.9 19; 20; B MET 01210 0.9 ± 0.18 <0.02 0.9 ± 0.2 0.9 3; A 1.4 ± 0.2 <0.03 1.4 ± 0.2 4 QUE 94281 <0.1 0.25 ± 0.1 0.35 ± 0.1 0.9 21; B Y-793274/981031 <0.025 0.04 ± 0.02 0.045 ± 0.025 1.1 16; B Th-rich mafic breccias SaU 169 <0.34 0.0097 ± 0.0013 0.175 ± 0.175 9 22; A Mare basalts NWA 032/479 0.042 <0.08 0.08 ± 0.02 1.9 23; A 0.023 <0.02 4 NWA 773 0.03 ± 0.002 0.017 ± 0.01 0.047 ± 0.004 0.6 2; B Asuka 881757 0.8 ± 0.2 0.4 11; B LAP 02205/02224/02226/02436/03632 0.35 ± 0.005 0.02 ± 0.005 0.055 ± 0.005 2.2 11; C 0.04 <0.1 4 Y-793169 0.9 ± 0.2 0.7 11; A in 1 and 10 Ma, respectively.
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