Shock recovery experiments on a Martian analogue rock (gabbro) loaded with three types of microorganisms reveal that these organisms survive the impact and ejection phase on Mars at shock pressures up to about 50 GPa with exponentially decreasing survival rates

Artemieva, N. A.

Cockell, C. S.

de Vera, J. P.

Fritz, J.

Horneck, G.

Hornemann, U.

Meyer, C.

Möller, R.

Ott, S.

Stöffler, D.

English

Open Research Online (The Open University)

Open Research OnlineThe Open University’s repository of research publicationsand other research outputsImpact experiments in support of “Lithopanspermia”:The route from Mars to EarthConference or Workshop ItemHow to cite:Sto¨ﬄer, D.; Meyer, C.; Fritz, J.; Horneck, G.; Mo¨ller, R.; Cockell, C. S.; Ott, S.; de Vera, J. P.; Hornemann,U. and Artemieva, N. A. (2006). Impact experiments in support of “Lithopanspermia”: The route from Mars to Earth.In: 37th Lunar and Planetary Science Conference, 13-17 Mar 2006, Houston, Texas.For guidance on citations see FAQs.c© 2006 The AuthorsVersion: Version of RecordLink(s) to article on publisher’s website:http://www.lpi.usra.edu/meetings/lpsc2006/pdf/1551.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.ukIMPACT EXPERIMENTS IN SUPPORT OF “LITHOPANSPERMIA”: THE ROUTE FROM MARS TO EARTH. D. Stöffler1, C. Meyer1, J. Fritz1, G. Horneck2, R. Möller2, C. Cockell3, S. Ott4, J. P. de Vera4, U. Horne-mann5, and N. A. Artemieva6. 1Museum für Naturkunde, Humboldt-University at Berlin, Germany, 2DLR, Institute for Aerospace Medicine, Cologne, Germany, 3Open University, Milton Keynes, UK, 4Institute of Botany, Univer-sity of Düsseldorf, Germany, 5Ernst-Mach-Institute, Freiburg i.Br., Germany, 6Institute for Dynamics of Geo-spheres, Russian Academy of Science, Moscow 119334, Russia, e-mail: dieter.stoeffler@rz.hu-berlin.de.   Introduction. Rather advanced knowledge on the physical and geological conditions for the transfer of solid rock fragments from Mars to Earth has been ac-quired recently by studying (a) the shock history of Martian meteorites [1, 2], (b) numerical models for the meteorites’ launch and transfer conditions [3, 4], and (c) the formation and cosmic ray exposure ages of these meteorites [2, 5]. It is therefore safe to assume that sizeable rock fragments [3] have been transferred from Mars to Earth at moderate p-T-conditions throughout its geological history. Shock pressures range from about 5 to 50 GPa and post-shock tempera-ture increases are mostly in the 10 to 600 °C range; however, the temperature effects are limited to rather short times due to rapid cooling during ejection. As various arguments had already lead to a revival of the 100 years old “panspermia” hypothesis [e.g., 6], the described facts and some pioneering shock and acceleration experiments with primitive microbes prompted the view that the possibility of a transfer of “endolithic” microbes from Mars to Earth has to be taken into consideration seriously [7, 8, 9]. This situa-tion has stimulated the present co-operative project in which three types of microorganisms embedded in a gabbro host rock were subjected to high shock pres-sures and recovered for the study of the survival rates. Experiments and samples. We performed shock recovery experiments using a high explosive set-up which has been previously applied to a great variety of silicate rocks and minerals to calibrate residual shock effects [e.g., 10]. The microbial test systems (bacterial endospores of Bacillus subtilis, the lichen Xanthoria elegans and the cryptoendolithic cyanobacterium Chroococcidiopsis) were subjected to shock pressures in the range observed in Martian meteorites [1]. Thin layers of microorganisms were embedded between two 0.5 mm thick plates of gabbro, encased in a steel con-tainer, and shocked to 10, 15, 20, 30, 40 and 50 GPa with pressure pulse durations ranging from 0.1 to 1.4 µs. Gabbro was used in the recovery experiments as a good analogue for the relatively coarse-grained basal-tic shergottites. After recovery, the actual shock pres-sure was determined by refractive index measurements of plagioclase grains separated from the shocked gab-bro using calibration data from [11]. The survival rates of the microorganisms were quantitatively determined using various biological and microscopic/electron mi-croscopic methods [e.g., 7]. Shock and post-shock temperatures were calculated on the basis of data in [3] and [1]. The shock-induced temperatures in the gabbro host rock are rather low due to the reverberation technique (shock and post shock-temperature increase ∆T of about 5 – 100 °C for less than 1.4 µs and about 5 – 60 °C for several min-utes, respectively, for pressures ranging from 10 to 50 GPa). They are clearly lower than in a natural single shock compression scenario. However, the post-shock temperatures achieved in the steel container pertaining for minutes (∆T = 10 – 350 °C) are most relevant, even more than the high shock temperature induced for less than 1 µs in the thin microbe layer due to its low shock impedance. Results. The pressure and temperature conditions and the measured survival rates of the microorganisms recovered from the six experiments are presented in Table 1. The basic result is that all three types of mi-crobes do survive the shock compression but the sur-vival rates which decrease exponentially with increas-ing pressure, approach zero values at different shock pressures. The symbiotic systems of the lichen Xan-thoria elegans display different survival rates: few hyphens of the mycobionts (0.002 %) survive at 50 GPa whereas the photobionts only reach an upper pressure limit of 31 GPa with a survival rate of 0.18 %. The endospores of Bacillus subtilis survive up to 42 GPa with a rate of 0.02 %. Chroococcidiopsis sur-vived only at 10 GPa with a rate of 0.39 % although this conclusion is preliminary and more data are re-quired to confirm this result. More details on the bio-logical aspects of these findings are given by [12, 13]. Conclusions. Our data provide evidence of a well-defined but limited launch window for the transfer of rock-inhabiting microorganisms from Mars to Earth by impact ejection involving shock pressures in the range from 5-10 GPa to 45 GPa. Shock and post-shock tem-peratures in the host rock and microbe layer have to be considered in relation to the low pre-shock tempera-tures at the surface and subsurface of Mars prevailing currently and probably over certain periods of its his-tory. Assuming a mean surface temperature of − 65 °C post-shock temperatures in gabbro or basalt would raise to roughly -50, -30, +50, and +400 °C at 10, 20, 30, and 40 GPa, respectively. Ultramafic rocks Lunar and Planetary Science XXXVII (2006) 1551.pdf(nakhlites) and some of the shergottites are most fa-vourable and efficient for the transfer of life from Mars to Earth, because they display the lowest degree of shock (5 – 30 GPa) and hence low post-shock heat-ing (∆T < 100 °C). Our experiments demonstrate that not only the prokaryotic Bacillus subtilis spores but also the eukaryotic lichen Xanthoria elegans are capa-ble of surviving in all types of Martian host rocks. The described scenarios are certainly only relevant if life ever existed on Mars. This would have required an at least temporary “warm and wet” Mars in the past. The recent debate on this issue is controversial as dis-cussed and referenced in [14]. We believe that the in-terpretation of the Mars Exploration Rover “Opportu-nity” data, i.e. the sedimentary layers with sulphates and clay minerals as impact induced base-surge depos-its in a cold and dry environment [14] is not supported by observations in terrestrial impact craters nor by impact-mechanical models. The formation of the sedi-mentary layered structures by aqueous deposition and  hence a once habitable environment in the “Opportu-nity” landing region is a more likely interpretation. Regardless of the outcome of this quest or data yields important insights into the basic potentials and limita-tions of “lithopanspermia”.  References. [1] Fritz J. et al. (2005) Meteoritics Planet. Sci., 9/10, 1393-1411. [2] Nyquist L. E. et al. (2001) Space Sci. Rev., 96, 105-164. [3] Artemieva N. A. & Ivanov B. A. (2004) Icarus, 171, 183-196. [4] Head J. N. et al. (2002) Science, 298, 1752-1756. [5] Eugster O. et al. (2002) Meteoritics Planet. Sci,. 37, 1345-1360. [6] Horneck G. et al. (1984) Science, 225, 226-228. [7] Horneck G. et al. (2001) Icarus, 149, 285-193. [8] Mastrapa R. M. E. et al. (2001) Earth Planet. Sci. Lett., 189, 1-8. [9] Mileikowsky C. et al. (2000) Icarus, 145, 391-427. [10] Stöffler D. & Lan-genhorst F. (1994) Meteoritics, 29, 155-188. [11] Stöffler D. et al. (1986) Geochim. Cosmochim. Acta, 50, 889-903. [12] Meyer et al. (2006) EGU meeting, Vienna, Abstract. [13] Horneck et al. (2006) Icarus, in preparation. [14] Bullock M. A. (2005) Nature, 438, 1087-1088 Acknowledgment. Financial support by the Ger-man Science Foundation (DFG) is gratefully acknowl-edged. We thank B. A. Ivanov for helpful contribu-tions. Table 1: Shock pressure (GPa) and survival rates of three types of microorganisms recovered from shock experiments Nominal pressure: calculated based on calibration runs in the shock reverberation mode; measured pressure: based on refractive indices of plagioclase from gabbro plates according to [11]; *calibration data for shocked plagioclase not available, **depending on detection method; 0 = below detection limit; - = no data Lunar and Planetary Science XXXVII (2006) 1551.pdf

Impact experiments in support of “Lithopanspermia”: The route from Mars to Earth

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Impact experiments in support of “Lithopanspermia”: The route from Mars to Earth

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