An Earth-Mars Transfer of Life: During the warm, wet Martian Noachian Lee Bardon, The Centre for Interdisciplinary Science Dr. John Bridges, Physics & Astronomy. ABSTRACT: We evaluate the likelihood of a viable, impact-driven exchange of microorganisms between Earth and the warm, wet Noachian Mars of ~ Ga. The evaluation is performed under three conceptual subsections: 1. Impact & Ejection, where an evaluation of the flux of asteroid and comet impacts on Earth and the subsequent ejecta is carried out via craterological analysis and impact modelling techniques. 2. The Interplanetary Phase, n- body simulations were conducted to track of the orbital paths of test particles ejected from 100 km above the Earth's surface. 655,362 particles were tracked and % were found to collide with Mars over a 30, 000 year simulation period. 3. Arrival & Proliferation on Noachian Mars and an analysis of the subaqueous surface area of Noachian Mars. Our results indicate that between ~2x10 5 and ~8x10 6 potentially viable life-bearing meteorite exchanges occurred between Earth and Mars during~ Ga. Image from NASA/JPL References: Carr, MH, (2006), ‘The Surface of Mars’, Cambridge University Press, UK. Chambers J.E., (1999), ‘A hybrid symplectic integrator that permits close encounters between massive bodies’, Monthly Notices of the Royal Astron. Soc., 304: Fassett,CI, & Head, JW., (2008), ‘Valley-network fed open basin lakes on Mars: Distribution and implications for Noachian surface and subsurface hydrology’, Icarus 198: Grotzinger, J.P. et al., (2014), Á habitable, fluvio-lacustrine environment at Yellowknife Bay, Gale Crater, Mars’, Science, 343: 6169, DOI: /science Losiak, A., et al., (2009), ‘A new Lunar impact database’, 40 th Lunar & Planetary Sciences Conference. Revised version by T. Ohman (2011) used. Marvin, U.B., (1983), ‘The discovery and initial characterization of Allan Hills Antarctic meteorite ALHA81005: The first Lunar meteorite’, Geophys. Res. Lett., 10: Melosh, H.J., (1984), ‘Impact ejection, spallation and the origin of meteorites’, Icarus, v. 59 (2): Melosh, H.J., (1987), ‘High velocity, solid ejecta fragments from hypervelocity impacts’, International Journal of Impact Engineering, v. 5(1-4): Mileikowsky, C., et al., (2000), ‘Natural transfer of viable microbes in space: 1 From Mars to Earth and Earth to Mars’, Icarus, v. 145 (2),: 391 – 427. Reyes-Ruiz M., Chavez C.E., Hernandez M.S., Vazquez R., Aceves H., and Nunez P.G. (2012) ‘Dynamics of escaping Earth ejecta and their collision probability with different Solar System bodies’, Icarus 220:777–786 Trieman A.H., et al., (2000), ‘The SNC meteorites are from Mars’, Planetary & Space Science, 48: LIFE ON MARS The n-body simulations described above allowed us to determine that % of the ejected material from Earth collides with Mars. As a final constraint, we estimate the subaqueous surface area of Noachian Mars, under the assumption that arriving Earth life is more likely to survive and proliferate if it lands in a region of abundant water. Conservatively, 0.01% of Mars was subaqueous, rising to 0.4% with less rigorous approach. Figure 2: Top Left: The location of ejected particles at launch (black band). Particles ejected from outside the band area were calculated to be very unlikely to interact with Mars. Bottom Left: The same data in a 2D projection. Bottom Right: Number of particle collisions with Mars over integration time (years). Figure 1: Top Left: Earth impacts during 4.0 – 3.5 Ga, in terms of Long/Short Period (LP/SP) comets and asteroids, according to crater diameter. Data obtained by scaling from Moon impact data collected by Losiak et al., (2011). Top Right: Cumulative number of fragments ejected per LP comet impact, according to impactor diameter, during 4.0 – 3.5 Ga. The fragments quantified are those ejected from the spall zone around the impact, meaning that they are likely to have experienced temperatures and pressures that modern extremophiles could have survived. Bottom Left/Right: The same data for SP comets and asteroids. 2. THE INTERPLANETARY PHASE Once the flux of potentially biologically-relevant material from Earth is constrained, we proceed to estimate the collision probability of that material with the surface of Mars. This is achieved through the implementation of a gravitational n-body simulation in the symplectic integration software environment Mercury 6.2 (Chambers, 1999), and with the collaboration of C. Chavez and M. Reyes-Ruiz at UNAM. Adapting and updating the approach utilized in Reyes-Ruiz et al., (2012), we track the orbital evolution of 655,362 test particles ejected from Earth, over a 30,000 year period: deemed relevant to the survival of microorganisms against the most biocidal extremes of space. Figure 3: The location of open-basin lakes (white circles), possible large crater lakes (red circles: 1. Hellas Basin; 2. Argyre Planitia; 3. Isidis Basin) and the proposed Ma’adim Vallis highland lake (red rectangle) on Noachian Mars. Image adapted from Fassett & Head (2008).